Safety circuits for modern batteries

A modern battery is a delicate storage device that requires protection to safeguard against damage. The most basic protection is a fuse that opens on excess current. Some fuses disengage permanently and render the battery useless once the filament is broken; other safety devices are resettable. The Polyswitch is such a resettable fuse. Connected into the battery's current path, this device creates a high resistance on excess current. The Polyswitch reverts to the low ON position when the condition normalizes, allowing operation to resume(Sony VGN-FZ11L battery).

Batteries used in hazardous areas must be intrinsically safe. Hazardous areas include oil refineries, mines, grain elevators and fuel handling at airports. These areas are typically serviced with two-way radios and computing devices. Intrinsically safe batteries prevent excessive heat buildup and the danger of an electric spark on equipment failure. Because of tight approval standards, intrinsically safe batteries carry twice to three-times the price tag of regular packs(Sony Vaio VGN-FZ31S battery).

Another battery that contains high-level protection is lithium-ion. This is done to assure safety under all circumstances while in the hands of the public. Typically, a Field Effect Transistor (FET) opens if the charge voltage of any cell reaches 4.30V. A separate fuse opens if the cell temperature approaches 90°C (194°F) (Sony Vaio VGN-FZ31Z battery). In addition, a disconnect switch in each cell permanently interrupts the charge current if a safe pressure threshold of about 10 Bar (150 psi) is exceeded. To prevent the battery from over-discharging, the control circuit cuts off the current path at about 2.50V/cell. Prolonged storage at voltages of 1.5V/cell and lower damages the lithium-ion, causing safety problems if attempted to recharge(Sony Vaio VGN-FZ38M battery).

Each parallel string of cells in a lithium-ion pack needs independent voltage monitoring. In addition, each cell in series must be monitored for voltage. The more cells that are connected in series, the more complex the protection circuit becomes. Four cells in series is the practical limit for commercial applications(Sony VGN-FZ11M battery).

The internal protection circuit must be designed to add as little resistance as possible to the current path. The circuit of a cell phone battery often consists of two FET switches connected in series. One FET is responsible for high, the other for low voltage cut-off. The combined resistance of the FETs in the ON position is 50-100milli Ohms (mW). This virtually doubles the internal resistance of a battery pack(Sony VGN-FZ11Z battery).

A major concern arises if static electricity or a faulty charger destroys the battery's protection circuit. This may result in permanently fusing the solid-state switches in an ON position without the user's knowledge. A battery with a faulty protection circuit may function normally but will not provide protection. If charged over a voltage limit (4.20V/cell should not be exceeded) with a defective charger, venting with flame could occur. Such a situation must be avoided at all cost. Shorting such a battery could also be hazardous(Sony VGN-FZ17 battery).

Low-cost cell phone batteries have infiltrated the world market since the beginning of 2003,. These counterfeit batteries often do not have an approved protection circuit and can vent with flame if the charger malfunctions. Cell phone manufacturers strongly advise customers to replace the battery with an approved brand. Failing to do so may void the warranty. It is also highly recommended to only use approved chargers(Sony VGN-FZ11S battery).

When advising on the choice of batteries and chargers, cell phone manufacturers act out of genuine concern for safety rather than using scare tactics to persuade customers to buy their own accessories. They do not object third parties as long as the products are well built and safe. The buyer can often not distinguish between an original and a counterfeit battery because the label may appear bona fide(Sony VGN-FZ180E battery).

Small lithium-ion packs with spinel (manganese) chemistry containing one or two cells may only include a fuse as protection. Spinel is more tolerant to abuse than cobalt and the cells are deemed safe if below a certain size(Sony VGN-FZ31E battery).

Although less expensive, the absence of a protection circuit introduces a new problem. Cell phone users have access to low-cost chargers that may rely on the battery's protection circuit to terminate charge. Without the protection circuit, the cell voltage rises too high and damages the battery. Excess heat, even bulging can result. Discontinue using the battery and charger if a lithium-ion battery gets hot(Sony VGN-FZ150E battery).

To maintain safe operation, manufacturers do not sell the lithium-ion cells by themselves but make them available in a battery pack, complete with protection circuit. The circuit is often subject to exact scrutiny before the manufacturers release cells to the pack assemblers. Although there are a few reported incidents of venting with flame, the lithium-ion battery is safe(SONY VAIO VGN-FZ4000 Battery).

The battery fuel gauge

When the 'smart' battery was introduced in the 1990s, one of the main objectives was to enable communications between the battery and user. Adding a fuel gauge solved this. In this paper, we evaluate various fuel gauges, check how they work, and assess their advantages and limitations. Since the System Management Bus (SMBus) is most widely used, we will focus on this system(Sony Vaio VGN-FZ battery).

The state-of-charge indicator
Most 'smart' batteries are equipped with a charge level indicator. When pressing the 'Test' button on a fully charged battery, all signal lights illuminate. On a partially discharged battery, half the lights illuminate, and on an empty battery, all lights remain dark. Figure 4 shows such a fuel gauge(Sony VGP-BPS8 battery).

While SoC information displayed on a battery or computer screen is helpful, the fuel gauge resets to 100% each time the battery is recharged, regardless of the battery's SoH. A serious miscount occurs if an aged battery shows 100% after a full-charge, when in fact the charge acceptance has dropped to say 50% or less. The question remains: "100% of what?" A user unfamiliar with this battery has little information about the runtime of the pack(Sony VGP-BPL9 battery).

The reserve capacity can only be established when the SoH is known. Figure 5 illustrates the three imaginary sections of a battery consisting of the empty zone, which can be refilled, available energy and unusable section or 'rock content' that can no longer store energy(Sony VGP-BPL11 battery).

A battery fuel gauge should be able to disclose all three sections of the battery. Knowing the battery's SoH can do this. While the SoC is relatively simple to produce, measuring the SoH is more complex. Here is how it works(Sony VGP-BPL15 battery):

At time of manufacture, each SMBus battery is given its specified SoH status, which is 100% by default. This information is permanently programmed into the pack and does not change. With each charge, the battery resets to the full-charge status. During discharge, the energy units (coulombs) are counted and compared against the 100% setting. A perfect battery would indicate 100% on a calibrated fuel gauge(Sony VGN-FZ460E battery). As the battery ages and the charge acceptance drops, the SoH decreases. The discrepancy between the factory-set 100% and the delivered coulombs on a fully discharged battery indicates the SoH(SONY VAIO VGN-FZ4000 Battery).

Knowing the SoC and SoH, a simple linear display can be made. The SoC is indicated with green LEDs; the empty part remains dark; and the unusable part is shown with red LEDs. Figure 6 shows such a tri-state fuel gauge. As an alternative, a numeric display indicating SoH and SoC can be used. The practical location for the tri-state-fuel gauge is on the charger(Sony VGP-BPS13 battery).

The target capacity selector

For users that simply need a go/no go answer, chargers are available that feature a target capacity selector. Adjustable to 60, 70 or 80%, the target capacity selector acts as a performance check and flags batteries that do not meet the set requirements(Sony VGN-FZ150E battery).

If a battery falls below target, the charger triggers the condition light. The user is prompted to press the condition button to calibrate and condition the battery by applying a charge/discharge/charge cycle. The green 'ready' light at the end of the service reveals full charge and assures that the battery meets the required performance level. If the battery does not recover, a fail light indicates that the battery should be replaced(Sony VGN-FZ15 battery). Figure 7 illustrates a two-bay Cadex charger featuring the target capacity selector and discharge circuit. This unit is based on Level 3 and services both SMBus and 'dumb' batteries.

By allowing the user to set the desired battery performance level, the question is raised as to what level to select. The answer is governed by the application, reliability and cost(Sony VGN-FZ31E battery).

The nominal target capacity setting is 80%. Decreasing the threshold to 70% will lower the performance standard but pass more batteries. A direct cost saving will result. The 60% level may suit those users who run a low budget operation, have ready access to replacement batteries and can live with shorter, less predictable runtimes. It should be noted that the batteries are always charged to 100%, regardless of the target setting. The target capacity simply reveals the energy, which a fully charged battery can deliver(Sony VGN-FZ17L battery).

'Smart' batteries enabling performance readings are reserved for high-end industrial applications. However, in spite of improvements made over the last ten years, the 'smart' battery, the SMBus in particular, has not received the anticipated acceptance. Some engineers go so far as to suggest that the SMBus battery is a 'misguided principal'(Sony VGN-FZ17G battery).

Part of the problem is the periodic calibration that is needed to correct the tracking errors that occur between the battery and the digital sensing circuit. Notable errors transpire if a battery is charged and discharged for only brief moments and the load varies widely. Long storage also contributes to errors because the circuit cannot accurately compensate for self-discharge(Sony VGN-FZ17 battery).

Regardless of these limitations, the 'smart' battery will continue to serve a critical market. It is conceivable that other methods will be introduced that do not rely on the in and out-flow of energy to establish energy reserve. But the importance of the fuel gauge has been established. There are simply no alternatives for users to whom unexpected downtime is no option(Sony VGN-FZ220E battery).

How to increase the runtime of your wireless device

As the sponsor of www.BatteryUniversity.com, Cadex Electronics gets many interesting enquiries from battery users. One writes, "Hi, I am looking for an answer to a perplexing question(Sony Vaio VGN-FZ battery). A co-worker and I have identical cell phones from the same provider. Moving into a new house, she complained of short battery runtime. I told her she was out of her mind, but then I noticed my battery behaving differently when I travel. Is there some mysterious force that's draining the battery(Sony VGP-BPS8 battery)?"

Yes, there is a force that's draining the battery. An active cell phone is in constant communication with the tower and consumes small bursts of energy once every second or so to check for incoming calls. The transmit power is adjusted to the signal strength. If the cell phone is close to a repeater tower, little energy is needed to communicate(Sony VGP-BPL9 battery). Moving further away or entering an environment with high electrical noise, such as a shopping mall, hospital or factory, more energy will be required. An analogy can be made to sitting in a restaurant. In a quiet establishment the voice can be low, but as the crowd grows, everyone needs to talk louder to be heard(Sony VGP-BPS9 battery).

Living in sight of a tower has advantages and your battery will run longer between charges. In essence, towers are the best friends to cell phone batteries. Even the placement of a cell phone in your house has an effect on runtime. At a recent meeting with a large cellular provider in the UK, a manager said that his son noticed short standby times after moving to his basement bedroom. If possible, leave your cell phone in an upstairs room facing a tower. When traveling by car, don't place your cell phone on the floor. Instead, raise it closer to window level but avoid direct exposure to the sun, as heat will harm the battery(Sony VGP-BPL11 battery).

The same energy savings apply to TETRA and P25 radio systems, cordless telephones, Wi-Fi and Bluetooth devices. A wireless headset that is communicating with your cell phone on the belt will provide longer runtimes than placing the handset on the dining table while doing the cooking. The Bluetooth headset needs to work harder when farther away from the user, although the quality of communication may not be affected(Sony VGP-BPL15 battery).

Just to clarify that the energy savings from the placement of a wireless device only apply when it's in the ON position. When OFF, the residual loads are very low; the battery needs only to supply power for housekeeping functions such as maintaining the clock. Housekeeping and self-discharge consume 5-10% of the available battery energy per month(Sony VGN-FZ460E battery).

During the last few years, standby and talk-times have much improved. The lithium-ion battery has doubled its energy density since its introduction in the early 1990s. In addition, large energy savings are being achieved in the receiver and demodulator circuits. Figure 1 illustrates the reduction of power consumption in these circuits since 2002(SONY VAIO VGN-FZ4000 Battery). We must keep in mind that this saving only applies to standby and receiving. Transmitting requires about five times the amount of power compared to receiving and demodulation. Modern handsets have also achieved better efficiencies in transmit circuits(Sony VGP-BPS13 battery).

It's not always the battery's fault

When the cell phone quits, the battery often gets the blame. The battery is the only user-replaceable part on a cell phone and becomes an easy target. Service personnel often replace the pack without testing, only to have the fault recur(Sony Vaio VGN-FZ21M battery ).

Moving from nickel-based to lithium-ion batteries eliminated many problems. Lithium-ion packs are maintenance free and don't require periodic full discharges to restore capacity; there is no memory effect. Still, customers suspect the batteries as the reason of most problems. As a result, large volumes of good packs are replaced and discarded. This is costing the cell phone industry ten million dollars annually. Cell phone providers say that 90% of returned batteries can easily be serviced(Sony VGN-FZ150E battery).

Technology is now available to rapid-test batteries at store level while the customer waits. If a replacement is needed, an exchange is given from a pool of batteries that had previously been serviced. On-site restorations eliminate courier charges and relieve manufacturers from the burden of handling tons of returned batteries(Sony VGN-FZ15 battery).

Figure 2 illustrates the service flow, starting with the customer bringing in the cell phone, checking the battery and providing a replacement. The replacement pack is taken from a pool that had previously been refurbished on site with a battery analyzer. A recent pilot test by a large service provider using this exchange program worked well and no replacement battery ever came back due to failure(Sony Vaio VGN-FZ18M battery).

According to a U.S. cellular provider, a typical store gets an average of ten returned batteries a day. The handling cost is estimated at $15US per pack. This amounts to a daily expense of $150 per store. Realizing this high expense and trying to cut cost, ten stores participated in a one-month experiment that involved examining and servicing incoming batteries using Cadex battery analyzers. During this study period, the stores saved 1981 batteries, resulting in a saving of about $30,000(Sony VGN-FZ31E battery).

Battery rapid-testing

One of the key features of a modern battery analyzer is obtaining accurate test results when rapid-testing a battery. In the past, the battery state-of-health was mostly estimated by measuring internal resistance. As Figure 3 shows, the battery's ability to hold energy (capacity) may not correspond with resistance. On some lithium-ion batteries, the capacity can drop to half its original level while maintaining low(Sony VGN-FZ180E battery).

For best results, a battery should be tested under similar conditions as used in the field. QuickSort™ by Cadex achieves this through a technology referred to as electrochemical dynamic response. This method can be compared to a mechanical arm under load. A strong arm remains firm, whereas a weak one bends and becomes sluggish when under load. This response can also be applied to estimating battery state-of-health. QuickSort™ provides a correct prediction 90% of the time over a wide population of lithium-ion batteries in various state-of-charge conditions(Sony VGN-FZ17 battery).

A relatively high number of batteries fail due to over-discharge. We discovered this while checking 1000 customer-returned packs that had been sent to the Cadex lab for further evaluation. Among these packs, 30% had no voltage reading and appeared dead. This was due to over-discharge(Sony VGP-BPS18 battery). At voltages between 2.5 and 2.8V, the internal safety circuit of a lithium-ion battery disengages and the battery goes into a sleep mode, making a recharge impossible. The Boost program of the Cadex C7000 Series battery analyzers activates the safety circuit and brings the battery back to life. The restoration is permanent and the pack can be returned to the customers(Sony VGN-FZ220E battery).

To prevent a cell phone battery from inadvertently falling asleep, apply a 30-minute charge (or longer) after the "Low Batt" indicator comes on. Do not store the cell phone in a totally discharged condition. Peripheral loads, combined with self-discharge, will further discharge the battery. This can lead to an eventual disconnect in which the battery appears dead as described above(Sony VGN-FZ11Z battery).

Besides rapid-test and boost, most battery analyzers also offer full battery service programs that consist of charge and discharge cycles. Such programs provide the most accurate battery assessment and are the recommended methods to prepare replacement batteries for exchange purposes. Figure 5 illustrates the Cadex C7400(Sony Vaio VGN-FZ31Z battery).

Observing batteries in everyday lives

Batteries have a mind of their own. Their stubborn and unpredictable behavior has left many battery users in awkward situations. And yet, the battery is our steady travel companion that allows us to carry out our activities disconnected from home and office. In this paper we observe the battery in personal use and fleet applications(Sony VGN-FZ11S battery).

The personal battery user

It is interesting to observe that batteries cared for by a single user generally last longer than those operating in an open fleet environment where everyone has access to but no one is accountable for them. A personal user is one who operates a mobile phone, a laptop or a video camera for pleasure or business(Sony Vaio VGN-FZ31Z battery). He or she will likely follow the recommended guidelines in caring for the battery. When the runtime gets low, the battery gets serviced or is replaced. Critical failures are rare because the owner adjusts to the performance of the battery and lowers the expectation as the battery ages(Sony Vaio VGN-FZ31M battery).

The fleet battery user

The fleet user, on the other hand, has little personal interest in the battery and has no tolerance for a pack that is less than perfect. He simply grabs a battery from the charger and expects it to last through the shift. The battery is returned to the charger at the end of the day, ready for the next person. Regular battery maintenance is minimal and performance often starts to degrade after one year of service(Sony VGN-FZ11M battery).

How can fleet batteries be made to last longer? I examined the US and the Dutch Army, both of which use fleet batteries. The US Army issues batteries with no maintenance program. If the battery fails, another pack is released, no questions asked. Little or no care is given and the failure rate is high(Sony VGN-FZ11Z battery).

The Dutch Army, on the other hand, has moved away from the open fleet system by making the soldiers responsible for their batteries. This change was made in an attempt to reduce operational costs and improve reliability. The batteries are issued to the soldiers and become part of their personal belongings. The results are startling. Since adapting this new regime, the failure rate has dropped considerably and the battery performance has increased. Unexpected down time has almost been eliminated(Sony VGN-FZ220E battery).

It should be noted that the Dutch Army uses exclusively nickel-cadmium batteries. Each pack receives periodic maintenance on a battery analyzer (Cadex) to prolong service life. Batteries that do not meet the 80% target capacity setting are reconditioned; those that fall below target are replaced. The US Army, on the other hand, uses nickel-metal-hydride, a battery that has higher energy density but is less durable. The US army is evaluating lithium-ion batteries for the next generation battery(Sony VGN-SZ55 battery).

What lack of battery maintenance can do

Batteries get checked when they no longer hold charge or the equipment is sent in for repair. In an effort to improve reliability and cut replacement costs, many organizations have adapted some type of battery maintenance(Sony VGP-BPS8 battery).

A user may feel that his or her battery works adequately during routine days, not knowing that the pack holds only half the capacity. A system must be fit to operate in unforeseen circumstances and emergencies where every watt of battery power is needed. Breakdowns during these critical moments are all too common and weak batteries are often to blame. The loss of adequate battery power is as detrimental as any other malfunction in the system(Sony Vaio VGN-FZ battery).
I have recorded a number of stories in which lack of battery maintenance was evident:

Fire brigade - A fire brigade had chronic communication problems with two-way radios. The problems were most acute during call-outs lasting two hours and longer. Although their radios functioned on receive, the transmissions broke up and the calls did not get through(Sony VGP-BPS9 battery).
The fire brigade acquired a battery analyzer (Cadex) and all batteries were serviced through exercise and recondition methods. Batteries that did not recover to a set target capacity were replaced(Sony VGP-BPL11 battery).

Shortly thereafter, the firefighters were summoned to a ten-hour call that demanded heavy radio traffic. To their astonishment, none of the radios failed. The success of this operation was credited to the good performance of their batteries. The following day, the captain of the fire brigade personally contacted the manufacturer of the battery analyzer and enthusiastically endorsed the use of the device(Sony VGP-BPL15 battery).

Emergency response - A Cadex representative was allowed to view the State Emergency Management Facility of a large US city. In the fortified underground bunker, 1400 batteries were kept in chargers. The green lights glowed, indicating that the batteries where ready at a moment's notice. The officer in charge stood erect and confidently said, "We are prepared for any emergency"(Sony VGN-FZ460E battery).

The representative then asked the officer to hand over a battery to check the state-of-health. Within seconds, the battery analyzer detected a fail condition. In an effort to make good, the officer grabbed another battery from the charger but it failed too. Subsequent batteries also fell short(SONY VAIO VGN-FZ4000 Battery).

nickel-based batteries placed on prolonged standby become inoperable due to memory in as little a three months. Scenarios such as these are common. Political hurdles and lack of funding often stand in the way of a quick solution. The only thing the officer can do is pray that no emergency will occur(Sony VGP-BPS13 battery).

Army - Defense organizations take great pride in employing the highest quality and best performing equipment. When it comes to rechargeable batteries, however, there are exceptions. The battery often escapes the scrutiny of a full military inspection and only its visual appearance is checked. Maintenance is frequently ignored and little effort is made in keeping track of the battery's state of health, cycle count and age. In time, the soldiers begin carrying rocks instead of batteries(Sony Vaio VGN-FZ21M battery ).

Batteries fooled the British Army during the Falkland War in 1982. The army assumed that a battery would always follow the rigid military specifications, even after long neglect. Not so. When the order was given to launch the portable missiles, nothing happened and the missiles did not fly that day. The batteries were dead(Sony VGN-FZ150E battery).

Government services - An organization continually experienced failures with nickel-cadmium batteries. Although the batteries performed at 100% when new, the capacity dropped to 20% and lower in only one year. We discovered that their two-way radios were under-utilized; yet the batteries received a full recharge after each short field use(Sony VGN-FZ31E battery).
After replacing the batteries, we advised the organization to exercise the batteries once per month through a full discharge. The first exercise occurred only after four month of service. Here is what we found(Dell RM791 battery):

The capacity on half of the batteries had dropped to 70-75%. With exercise and recondition (deep cycle), all batteries were fully restored (100%). Had maintenance been omitted for much longer, the probability of a full recovery would have been jeopardized(Dell Latitude E6400 battery).

Construction - I noticed fewer battery problems on two-way radios with construction workers than security guards. The construction workers often did not bother turning off their two-way radios at the end of the shift. As a result, the nickel-cadmium batteries got their needed exercise and kept performing until they fell apart from old age, often held together with duct tape(Dell Latitude E6500 battery).

In comparison, the security guards pampered their batteries to death by giving them light duty and plenty of recharge. These batteries still looked new when they had to be discarded after only 12 months of service. Because of the advanced memory, recondition was no longer effective(Toshiba NB100 battery).

Observing batteries in everyday lives

Batteries have a mind of their own. Their stubborn and unpredictable behavior has left many battery users in awkward situations. And yet, the battery is our steady travel companion that allows us to carry out our activities disconnected from home and office. In this paper we observe the battery in personal use and fleet applications (Sony Vaio VGN-FZ battery).

The personal battery user

It is interesting to observe that batteries cared for by a single user generally last longer than those operating in an open fleet environment where everyone has access to but no one is accountable for them. A personal user is one who operates a mobile phone, a laptop or a video camera for pleasure or business(Sony VGP-BPS8 battery). He or she will likely follow the recommended guidelines in caring for the battery. When the runtime gets low, the battery gets serviced or is replaced. Critical failures are rare because the owner adjusts to the performance of the battery and lowers the expectation as the battery ages(Sony VGP-BPL9 battery).

The fleet battery user

The fleet user, on the other hand, has little personal interest in the battery and has no tolerance for a pack that is less than perfect. He simply grabs a battery from the charger and expects it to last through the shift. The battery is returned to the charger at the end of the day, ready for the next person. Regular battery maintenance is minimal and performance often starts to degrade after one year of service (Sony VGP-BPS9 battery).

How can fleet batteries be made to last longer? I examined the US and the Dutch Army, both of which use fleet batteries. The US Army issues batteries with no maintenance program. If the battery fails, another pack is released, no questions asked. Little or no care is given and the failure rate is high(Sony VGP-BPL15 battery).

The Dutch Army, on the other hand, has moved away from the open fleet system by making the soldiers responsible for their batteries. This change was made in an attempt to reduce operational costs and improve reliability. The batteries are issued to the soldiers and become part of their personal belongings. The results are startling. Since adapting this new regime, the failure rate has dropped considerably and the battery performance has increased. Unexpected down time has almost been eliminated(Sony VGN-FZ460E battery).

It should be noted that the Dutch Army uses exclusively nickel-cadmium batteries. Each pack receives periodic maintenance on a battery analyzer (Cadex) to prolong service life. Batteries that do not meet the 80% target capacity setting are reconditioned; those that fall below target are replaced. The US Army, on the other hand, uses nickel-metal-hydride, a battery that has higher energy density but is less durable. The US army is evaluating lithium-ion batteries for the next generation battery(SONY VAIO VGN-FZ4000 Battery).

What lack of battery maintenance can do

Batteries get checked when they no longer hold charge or the equipment is sent in for repair. In an effort to improve reliability and cut replacement costs, many organizations have adapted some type of battery maintenance(Sony VGP-BPS13 battery).

A user may feel that his or her battery works adequately during routine days, not knowing that the pack holds only half the capacity. A system must be fit to operate in unforeseen circumstances and emergencies where every watt of battery power is needed. Breakdowns during these critical moments are all too common and weak batteries are often to blame. The loss of adequate battery power is as detrimental as any other malfunction in the system(Sony Vaio VGN-FZ21M battery ).
I have recorded a number of stories in which lack of battery maintenance was evident:

Fire brigade - A fire brigade had chronic communication problems with two-way radios. The problems were most acute during call-outs lasting two hours and longer. Although their radios functioned on receive, the transmissions broke up and the calls did not get through(Sony VGN-FZ150E battery).
The fire brigade acquired a battery analyzer (Cadex) and all batteries were serviced through exercise and recondition methods. Batteries that did not recover to a set target capacity were replaced(Sony Vaio VGN-FZ18M battery).

Shortly thereafter, the firefighters were summoned to a ten-hour call that demanded heavy radio traffic. To their astonishment, none of the radios failed. The success of this operation was credited to the good performance of their batteries. The following day, the captain of the fire brigade personally contacted the manufacturer of the battery analyzer and enthusiastically endorsed the use of the device(Sony VGN-FZ31E battery).

Emergency response - A Cadex representative was allowed to view the State Emergency Management Facility of a large US city. In the fortified underground bunker, 1400 batteries were kept in chargers. The green lights glowed, indicating that the batteries where ready at a moment's notice. The officer in charge stood erect and confidently said, "We are prepared for any emergency"(Sony VGN-FZ180E battery).

The representative then asked the officer to hand over a battery to check the state-of-health. Within seconds, the battery analyzer detected a fail condition. In an effort to make good, the officer grabbed another battery from the charger but it failed too. Subsequent batteries also fell short(Sony VGP-BPS18 battery).

nickel-based batteries placed on prolonged standby become inoperable due to memory in as little a three months. Scenarios such as these are common. Political hurdles and lack of funding often stand in the way of a quick solution. The only thing the officer can do is pray that no emergency will occur(Sony VGN-FZ220E battery).

Army - Defense organizations take great pride in employing the highest quality and best performing equipment. When it comes to rechargeable batteries, however, there are exceptions. The battery often escapes the scrutiny of a full military inspection and only its visual appearance is checked. Maintenance is frequently ignored and little effort is made in keeping track of the battery's state of health, cycle count and age. In time, the soldiers begin carrying rocks instead of batteries(Sony Vaio VGN-FZ31Z battery).

Batteries fooled the British Army during the Falkland War in 1982. The army assumed that a battery would always follow the rigid military specifications, even after long neglect. Not so. When the order was given to launch the portable missiles, nothing happened and the missiles did not fly that day. The batteries were dead(Sony Vaio VGN-FZ31M battery).

Government services - An organization continually experienced failures with nickel-cadmium batteries. Although the batteries performed at 100% when new, the capacity dropped to 20% and lower in only one year. We discovered that their two-way radios were under-utilized; yet the batteries received a full recharge after each short field use(Sony VGN-FZ11Z battery).
After replacing the batteries, we advised the organization to exercise the batteries once per month through a full discharge. The first exercise occurred only after four month of service. Here is what we found(Sony VGN-FZ11M battery):

The capacity on half of the batteries had dropped to 70-75%. With exercise and recondition (deep cycle), all batteries were fully restored (100%). Had maintenance been omitted for much longer, the probability of a full recovery would have been jeopardized(Dell Latitude E6400 battery).

Construction - I noticed fewer battery problems on two-way radios with construction workers than security guards. The construction workers often did not bother turning off their two-way radios at the end of the shift. As a result, the nickel-cadmium batteries got their needed exercise and kept performing until they fell apart from old age, often held together with duct tape(Dell Latitude E6500 battery).

In comparison, the security guards pampered their batteries to death by giving them light duty and plenty of recharge. These batteries still looked new when they had to be discarded after only 12 months of service. Because of the advanced memory, recondition was no longer effective(Toshiba NB100 battery).

Discharging at high and low temperature

Batteries function best at room temperature. Operating batteries at an elevated temperature dramatically shortens their life. Although a lead-acid battery may deliver the highest capacity at temperatures above 30°C (86°F), prolonged use under such conditions decreases the life of the battery(Toshiba NB200 battery). Similarly, a lithium-ion performs better at high temperatures. Elevated temperatures temporarily counteract the battery's internal resistance, which may have advanced as a result of aging. The energy gain is short-lived because elevated temperature promotes aging by further increasing the internal resistance(Toshiba NB100 battery).

There is one exception to running a battery at high temperature - it is the lithium-polymer with dry solid polymer electrolyte, the true 'plastic battery'. While the commercial lithium-ion polymer uses some moist electrolyte to enhance conductivity, the dry solid polymer version depends on heat to enable sufficient ion flow. This requires that the battery core be kept at an operation temperature of 60°C to 100°C (140°F to 212°F) (Toshiba PA3399U-2BRS battery).

The dry solid polymer battery has found a niche market as backup power in warm climates. The battery is kept at the operating temperature with built-in heating elements that is fed by the utility grid during normal operation. On a power outage, the battery would need to provide its own power to maintain the temperature. Although said to be long lasting, price is an obstacle(Toshiba PA3399U-1BRS battery).

Nickel-metal-hydride degrades rapidly if cycled at higher ambient temperatures. For example, if operated at 30°C (86°F), the cycle life is reduced by 20%. At 40°C (104°F), the loss jumps to a whopping 40%. If charged and discharged at 45°C (113°F), the cycle life is only half of what can be expected if used at moderate room temperature. The nickel-cadmium is also affected by high temperature operation, but to a lesser degree(Dell Latitude E6500 battery).

At low temperatures, the performance of all battery chemistries drops drastically. While -20°C (-4°F) is threshold at which the nickel-metal-hydride, sealed lead-acid and lithium-ion battery cease to function, the nickel-cadmium can go down to -40°C (-40°F). At that frigid temperature, the nickel-cadmium is limited to a discharge rate of 0.2C (5 hour rate). There are new types of Li?ion batteries that are said to operate down to -40°C(Dell Latitude E6400 battery).

It is important to remember that although a battery may be capable of operating at cold temperatures, this does not automatically allow charging under those conditions. The charge acceptance for most batteries at very low temperatures is extremely confined. Most batteries need to be brought up to temperatures above the freezing point for charging. Nickel-cadmium can be recharged at below freezing provided the charge rate is reduced to 0.1C(Dell Studio 1735 battery).

Lithium-ion works within the discharge temperature limits of -20°C to 60°C (-4°F to 140°F). The performance is temperature based, meaning that the rate capability at or below -20°C is reduced due to the increased impedance of the electrolyte. Discharging at low temperatures does not harm the battery. Lithium-ion may be used down to -30°C (-22°F) with acceptable results. Larger packs will be necessary to compensate for the reduced capacity at these temperatures(Dell RM791 battery).
It is not recommended to discharge lithium-ion at temperatures above 60°C. A high discharge rates combined with elevated temperatures can cause self-heating, an effect that could permanently damage the separator and electrodes of the cells(Sony Vaio VGN-FZ31Z battery).

It is not recommended to discharge lithium-ion at temperatures above 60°C. A high discharge rates combined with elevated temperatures can cause self-heating, an effect that could permanently damage the separator and electrodes of the cells(Sony Vaio VGN-FZ31M battery).

Pulse discharge

Battery chemistries react differently to specific loading requirements. Discharge loads range from a low and steady current used in a flashlight, to sharp current pulses for digital communications equipment, to intermittent high current bursts in a power tool and to a prolonged high current load for an electric vehicle traveling at highway speed(Sony VGN-FZ11S battery). Because batteries are chemical devices that must convert higher-level active materials into an alternate state during discharge, the speed of such transaction determines the load characteristics of a battery. Also referred to as concentration polarization, the nickel and lithium-based batteries are superior to lead-based batteries in reaction speed(Sony VGN-FZ11Z battery).

Although lithium-ion battery packs are equipped with a current limiter for safety reasons, the cell is capable of delivering high current pulses of one second and less in duration. On applications with high current spikes, a special protection circuit will be needed that allows high-current pulses but provides protection on a continuous overload condition(Sony VGN-FZ220E battery).

A lithium-ion battery manufacturer claims that their cells perform better on a pulse rather than DC load. The DC resistance of their 18650 cylindrical cell is ~110 mOhm. At 1 KHz AC, the impedance goes down to ~36 mOhm. As the pulses increase in frequency, the cell's effective impedance goes down. This results in better performance and lower heat build-up. These two effects increase the life of the lithium-ion cell(Sony VGN-FZ11M battery).

The internal resistance of the cobalt-based lithium-ion will increase with age and cause a problem when drawing heavy pulse currents. The manganese-based cell, on the other hand, will maintain the resistance at a low level throughout its service life. The cobalt-based lithium-ion cell provides a higher energy density but manganese is better suited for pulse load applications(Sony VGP-BPS15 battery).

The lead-acid battery performs best at a slow 20-hour discharge. A pulse discharge also works well because the rest periods between the pulses help to disperse the depleted acid concentrations back into the electrode plate. A discharge at 1C of the rated capacity yields the poorest efficiency. The lower level of conversion, or increased polarization, manifests itself in a momentary higher internal resistance due to the depletion of active material in the reaction(Sony VGP-BPS18 battery).

Different discharge methods, notably pulse discharging, affect the longevity of some battery chemistries. While nickel-cadmium and lithium-ion are robust and show minimal deterioration when pulse discharged, the nickel-metal-hydride exhibits a reduced cycle life when powering a digital load(Sony VGN-FZ31E battery).

In a recent study, the longevity of nickel-meal-hydride was observed by discharging with analog and digital loads to 1.04V/cell. The analog discharge current was 500mA; the digital mode simulated the load requirements of the Global System for Mobile Communications (GSM) protocol and applied 1.65-ampere peak current for 12 ms every 100 ms and a standby current of 270mA. (Note that the GSM pulse for voice is about 550 ms every 4.5 ms) (Sony VGN-FZ150E battery).

With the analog discharge, the nickel-metal-hydride provided an above average service life. At 700 cycles, the battery still provided 80% capacity. By contrast, the cells faded more rapidly with a digital discharge. The 80% capacity threshold was reached after only 300 cycles. This phenomenon indicates that the kinetic characteristics for the nickel-metal-hydride deteriorate more rapidly with a digital rather than an analog load. lithium and lead-acid systems are less sensitive to pulsed discharge than nickel-metal-hydride(Sony Vaio VGN-FZ battery).

Discharge methods

The purpose of a battery is to store energy and release it at the appropriate time in a controlled manner. In this section we examine the discharge under different C-rates and evaluate the depth to which a battery can safely be discharged. We also observe how deep discharges affect battery life(Toshiba NB200 battery).

What is C-rate?

The charge and discharge current of a battery is measured in C-rate. Most portable batteries are rated at 1C. This means that a 1000mAh battery would provide 1000mA for one hour if discharged at 1C rate. The same battery discharged at 0.5C would provide 500mA for two hours. At 2C, the 1000mAh battery would deliver 2000mA for 30 minutes. 1C is often referred to as a one-hour discharge; a 0.5C would be a two-hour, and a 0.1C a 10-hour discharge(Toshiba NB100 battery).
The capacity of a battery is commonly measured with a battery analyzer. If the analyzer's capacity readout is displayed in percentage of the nominal rating, 100% is shown if a 1000mAh battery can provide this current for one hour. If the battery only lasts for 30 minutes before cut-off, 50% is indicated. A new battery sometimes provides more than 100% capacity(Toshiba PA3399U-1BRS battery).

When discharging a battery with a battery analyzer that allows the setting of different discharge C-rates, a higher capacity reading is observed if the battery is discharged at a lower C-rate and vice versa. By discharging the 1000mAh battery at 2C, or 2000mA, the analyzer is scaled to derive the full capacity in 30 minutes(Toshiba PA3399U-2BRS battery). Theoretically, the capacity reading should be the same as with a slower discharge, since the identical amount of energy is dispensed, only over a shorter time. Due to internal energy losses and a voltage drop that causes the battery to reach the low-end voltage cut-off sooner, the capacity reading may be lowered to 95%. Discharging the same battery at 0.5C, or 500mA over two hours may increase the capacity reading to about 105%. The discrepancy in capacity readings with different C-rates is related to the internal resistance of the battery(Dell Latitude E6500 battery).

One battery that does not perform well at a 1C discharge rate is the portable sealed lead-acid. To obtain a reasonably good capacity reading, manufacturers commonly rate these batteries at 0.05C or 20 hour discharge. Even at this slow discharge rate, a 100% capacity is hard to attain(Dell Latitude E6400 battery). To compensate for different readings at various discharge currents, manufacturers offer a capacity offset. Applying the offset to correct the capacity readout does not improve battery performance; it merely adjusts the capacity calculation if discharged at a higher or lower C-rate than specified(Dell RM791 battery).

Lithium-ion/polymer batteries are electronically protected against high load currents. Depending on battery type, the discharge is limited to between 1C and 2C. This protection makes the lithium ion unsuitable for biomedical equipment and power tools demanding high inrush currents(Sony VGN-FZ11S battery).

Depth of discharge

The typical end-of-discharge voltage for nickel-based batteries is 1V/cell. At that voltage level, roughly 99% of the energy is spent and the voltage starts to drop rapidly if the discharge continued. Discharging beyond the cut-off voltage must be avoided, especially under heavy load(Sony Vaio VGN-FZ31Z battery).

Since the cells in a battery pack cannot be perfectly matched, a negative voltage potential, also known as cell reversal, will occur across a weaker cell if the discharge is allowed to continue uncontrolled. The more cells that are connected in series, the greater the likelihood of cell reversal occurring(Sony Vaio VGN-FZ31M battery).

Nickel-cadmium can tolerate some cell reversal, which is typically about 0.2V. During that time, the polarity of the positive electrode is reversed. Such a condition can only be sustained for a brief moment because hydrogen evolution on the positive electrode leads to pressure build-up and possible cell venting. If the cell is pushed further into voltage reversal, the polarity of both electrodes is being reversed and the cell produces an electrical short. Such a fault cannot be corrected(Sony VGN-FZ31E battery).

Some battery analyzers apply a secondary discharge (recondition) that discharges the battery voltage to a very low voltage cut-off point. These instruments control the discharge current to assure that the maximum allowable current, while in sub-discharge range, does not exceed a safe limit. Should cell reversal develop, the current would be low enough not to cause damage. Cell breakdown through recondition is possible on a weak or aged pack(Sony VGN-FZ61B battery).

If the battery is discharged at a rate higher than 1C, the end-of-discharge point of a nickel-based battery is typically lowered to 0.9V/cell. This compensates for the voltage drop induced by the internal resistance of the cells, wiring, protection devices and contacts. A lower cut-off point also produces better capacity readings when discharging a battery at cold temperatures(Sony VGN-FZ180E battery).

Among battery chemistries, nickel-cadmium is least affected by repeated full discharge cycles. Several thousand charge/discharge cycles are possible. This is why nickel-cadmium performs well on power tools and two-way radios that are in constant use. nickel-metal-hydride is less durable in respect to repeated deep cycling(Sony VGN-FZ11Z battery).

Lithium-ion typically discharges to 3.0V/cell. The spinel and coke versions can be discharged to 2.5V/cell to gain a few extra percentage points. Since the equipment manufacturers do not specify the battery type, most equipment is designed for a 3-volt cut-off(Sony Vaio VGN-FZ battery).

A discharge below 2.5V/cell may put the battery's protection circuit to sleep, preventing a recharge with a regular charger. These batteries can be restored with the Boost program available on the Cadex C7000 Series battery analyzers(Sony VGP-BPS8 battery).

Some lithium-ion batteries feature an ultra-low voltage cut-off that permanently disconnects the pack if a cell dips below 1.5V. A very deep discharge may cause the formation of copper shunt, which can lead to a partial or total electrical short. The same occurs if the cell is driven into negative polarity and is kept in that state for a while(Sony VGP-BPL9 battery).

Manufacturers rate the lithium-ion battery at an 80% depth of discharge. Repeated full (100%) discharges would lower the specified cycle count. It is therefore recommended to charge lithium-ion more often rather than letting it discharge down too low. Periodic full discharges are not needed because lithium-ion is not affected by memory(Sony VGP-BPS9 battery).

The recommended end-of-discharge voltage for lead-acid is 1.75V/cell. The discharge does not follow the preferred flat curve of nickel and lithium-based chemistries. Instead, Lead-acid has a gradual voltage drop with a rapid drop towards the end of discharge(Sony VGP-BPL11 battery).

The cycle life of sealed lead-acid is directly related to the depth of discharge. The typical number of discharge/charge cycles at 25°C (77°F) with respect to the depth of discharge is:

• 150 - 200 cycles with 100% depth of discharge (full discharge)
• 400 - 500 cycles with 50% depth of discharge (partial discharge)
• 1000 and more cycles with 30% depth of discharge (shallow discharge)

The lead-acid battery should not be discharged beyond 1.75V per cell, nor should it be stored in a discharged state. The cells of a discharged lead-acid sulfate, a condition that renders the battery useless if left in that state for a few days. Always keep the open terminal voltage at 2.10V and higher(Sony VGN-FZ460E battery).

Discharge currents and load signatures

Rechargeable batteries are tolerant to wide range of load signatures. In terms of cycle life, a constant current discharge is better than a digital load(Sony VGP-BPL15 battery).

What constitutes a discharge cycle?

There are no standard definitions that constitute a discharge cycle. Smart batteries that keep track of discharge cycles commonly use a depth-of-discharge of 70% to define a discharge cycle. Anything less than 70% does not count. The reason of the cycle count is to estimate the end-of-battery life(SONY VAIO VGN-FZ4000 Battery).

A battery often receives many short discharges with subsequent recharges. With the smart battery, these cycles do not count because they stress the battery very little. On satellites, the depth-of-discharge is only about 10%. Such minute discharge cycles put the least amount of stress on the batteries in space. With shallow discharges, however, nickel-based batteries require a periodic deep discharge to eliminate memory(Sony VGP-BPS13 battery).

Lithium and lead-based batteries do not require a periodic full discharge. In fact, it is better not to discharge them too deeply but charge them more often. Using a larger battery is one way to reduce the stress on a battery(Sony VGN-FZ150E battery).

What's the best battery for wheeled and stationary applications?

Consumer products have benefited the most from the advancements in battery technology. The size and weight reductions achieved for the high-end cell phones, PDA's and laptops have not trickled down to batteries for wheeled and stationary applications in an expected fashion. Only marginal improvements have been gained on larger batteries. One of the reasons for the apparent lack in progress is the loyalty to the classic sealed lead-acid battery (Sony Vaio VGN-FZ battery).

The wheeled and stationary industries have several reasons for their unwillingness to change: [1] lead-acid is mature and inexpensive. [2] The low energy density is no major drawback because the battery is either on wheels or is stationary. [3] The limited cycle life can, to some extent, be compensated by using larger batteries. Unlike portable devices, most wheeled and stationary batteries are replaced due to age rather than wear out effect induced by high cycle count (Sony VGP-BPS8 battery).

What's the best battery for wheelchairs?

Wheelchairs and scooters are almost exclusively powered by sealed lead-acid batteries. Regular car batteries are sometimes used for cost reasons. There is, however, a danger of spillage if overturned. Neither are regular car batteries designed for deep cycling. The demanding cycling regiments of wheelchairs and scooters cause an undue strain on these batteries and shorten their lives. nickel-based batteries would be lighter than lead-acid but are more expensive and maintenance prone. Lithium-ion would simply be too delicate, not to mention the high cost (Sony VGP-BPS9 battery).

A new generation of wheelchair is being developed that is able to 'stand up' and climb stairs. These high-tech devices use gyroscopes for balancing. To obtain the extra power needed to run its internal computer and electric motors without adding too much weight, nickel-based batteries are used. The two-wheeled Segway scooter being touted to solve city transportations problems also uses nickel-based batteries (Sony VGN-FZ460E battery).

What's the best battery for the electric bicycle?

Anyone serious about the electric bicycle would use nickel-based batteries. Sealed lead-acid is simply too heavy and does not provide the cycle count needed to satisfy daily use. In addition, lead-acid requires a long charge time of 10 hours and more. Lithium-ion would simply be too expensive and delicate. The lack of a suitable battery that is light, durable and inexpensive is, in my opinion, delaying the public acceptance of the electric bicycle (Sony VGP-BPL15 battery).

What's the best battery for the electric vehicle?

The electric vehicle will gain public acceptance as soon as a battery emerges that is inexpensive and provides 10 years of reliable service. The high cost and limited cycle life of the batteries used in hybrid vehicles negate the savings achieved in burning less fuel. The benefits are more environmental in nature rather than in cost savings. Higher fuel prices could change this equilibrium (SONY VAIO VGN-FZ4000 Battery).

nickel and lithium-based batteries have been tried but both chemistries have problems with durability and stability. lithium-ion has an advantage in weight but this gain is offset by a high price. Similarly, nickel-metal-hydride used for the hybrid vehicle is expensive and requires forced air-cooling. No battery manufacturer is willing to commit to a 10-year warranty. After excursions into new battery chemistries, design engineers always come back to the old but proven lead-acid (Sony VGP-BPS13 battery).

The fuel cell may still be two decades away before offering a viable alternative for cars. An executive from Ford stated recently that the fuel cell may never be feasible to replace the internal combustion engine. Cost and longevity remain major drawbacks (Sony VGN-FZ150E battery).

Since the invention in 1839 by Sir William Grove, the advancements in the fuel cell have been slow. Much attention was then placed on improving the internal combustion engine. It was not until the Gemini and Apollo programs in the 1960s that the fuel cell was used to provide power and water in space. During the 1990s, renewed activities took place and the fuel cell stocks soared (Sony Vaio VGN-FZ18M battery). Unlike the rapid developments in microelectronics, which generated income in its early stages, fuel cell research continues to depend on government grants and public investors. It is our hope that one day the fuel cell will become a viable option to the polluting combustion engine (Sony VGN-FZ31E battery).

What's the best battery for stationary applications?

Until the mid 1970s, most stationary batteries were flooded lead-acid. The Valve Regulated Lead Acid (VRLA) allowed batteries to be installed in smaller confinements because the cells could be stacked and mounted in any position. Although VRLA are less durable than flooded lead-acid, simple mounting and lower cost make them the preferred battery system for small and medium sized installations. Most UPS systems repeater stations for cell phones use VRLA. Large installations, such as internet hubs, hospitals, banks and airports still use the flooded lead-acid (Sony VGN-FZ11Z battery).

Heat is the main killer of batteries. Many outdoor installations for communication systems lack proper venting, not to mention air conditioning. Instead of the expected 10-year service life, the batteries need replacement after 2 to 5 years. Many batteries in the field are in such bad conditions that they could only provide power for a short time, should a major power outage occur. Stationary batteries are often installed and forgotten (Sony VGN-FZ11M battery).

A Canadian manufacturer of lithium-polymer batteries is taking advantage of the heat problem. They offer lithium-polymer for standby applications, a battery that needs heat to operate. The dry lithium-polymer lacks conductivity at ambient temperature and must be heated. The battery includes heating elements to keep its core temperature at 60°C (140°F) (Sony Vaio VGN-FZ31M battery). The mains provide the energy for heating. On a power outage, the battery must also provide power for heating the core. To conserve energy, the battery is well insulated. Unlike the VRLA, the high ambient heat does not shorten the lithium-polymer battery. The high cost remains a drawback and only a few lithium-polymer batteries are used for stationary applications today (Sony Vaio VGN-FZ31Z battery).

Flooded nickel-cadmium batteries have been used for many years in applications that must endure hot and cold temperatures. This battery system is substantially more expensive that Lead-acid but the improved longevity makes up for the higher investment cost. The flooded nickel-cadmium batteries are non-sintered and do not suffer from memory. It should be noted that only the sintered sealed nickel-cadmium cells are affected by memory and need regular discharges (Sony VGN-FZ11S battery).

The miniature fuel cell

For a long time, manufacturers have been exploring ways to replace the electrochemical battery. Higher energy densities, smaller size, lower cost per watt and faster charging are on the wish list. Electrical energy from rechargeable batteries is expensive when considering the high purchase price, the limited life span and the small amount of power they can deliver (Sony Vaio VGN-FZ battery).

Will the fuel cell replace the battery?

During the last years, fuel cell technology has gained much hype and many see this power source as the gateway to the future. Since its invention in 1839 by Sir William Grove, the fuel cell remained a scientific oddity until the 1950s when it was used for US space and military programs for the first time (Sony VGP-BPS8 battery). In the 1980s, the fuel cell had another rebirth when scientists and stock promoters envisioned a world powered by a clean power source fed by an inexhaustible fuel, hydrogen. They forecasted that cars would be run by fuel cells and households be powered by electricity generated from back-yard fuel cell units. High manufacturing costs and short service life have been in the way of making this a reality (Sony VGN-FZ460E battery).

The fuel cell uses hydrogen and oxygen as fuel. Combining the two gases generates electricity and water. There is not combustion; no pollution. The byproduct is pure water. The system runs so clean that Ballard, a developer of fuel cell stacks, offered the guests tea from the hot water produced by the fuel cell. This makes it possible to run a fuel cell in an enclosed room, such as an office of living room. The theoretical energy output of the fuel cell is high, but over half is lost in heat (SONY VAIO VGN-FZ4000 Battery).

During the past years, portable versions of the fuel cells have emerged. The most promising miniature fuel cell is the direct methanol fuel cell (DMCF). DMCF is inexpensive, convenient, does not require pressurized hydrogen gas and provides a reasonably good electrochemical performance(Sony VGP-BPS13 battery). Current systems produce 900 Wh of power and offer an energy density of 102 Wh/l. This is still large in size compared to an electrochemical battery and further reductions will be needed. Charging consists of replacing the cartridge on the fly. This provides a continued source of energy, similar to fueling a car (Sony VGN-FZ150E battery).

Toshiba unveiled a prototype fuel cell for a laptop but described the technology as being in its 'infancy.' The company gave no indication as to when the product would be commercially available. A direct battery replacement that offers high power, small size and competitive price is still several years away. Figure 1 shows a DMFC by Toshiba. The micro fuel cell on the left is capable of providing 300mW of continuous power. The fuel is 99.5% pure methanol stored in a 10 mL tank (Sony Vaio VGN-FZ18M battery). The refueling process is shown on the right.
Angstrom Power is developing a portable fuel cell that runs on stored hydrogen and oxygen from the air. The system operates at ambient conditions and has no pump and fan. The advantage of pure hydrogen over methanol is increased efficiency and smaller size. The aim is to offer a power source that is clean, quiet and can be refueled on the fly (Sony VGN-FZ61B battery).

According to Angstrom Power, the micro hydrogen™ bike lights have delivered good performance in winter and spring conditions and the user feedback is positive. The hydrogen fuel is stored in a 21cc cartridge, providing the equivalent energy of about 10 AA disposable alkaline batteries. The only by-product is water vapor. Refueling takes a few minutes and provides a continuous runtime of about 20 hours (Sony VGN-FZ31E battery).
As good as the fuel cell may look from the outside, 15-years of experiments has not solved a number of persistent problems. One is the slow start-up; another is the low electrochemical activity at the anode. This is especially apparent with the DMCF. Each cell produces about one volt and when loaded, the relatively high internal resistance causes the voltage drops quickly (Sony VGN-FZ180E battery).

Current loading is not critical with a small bicycle light, especially when low-drain LED technology is used. A laptop, on the other hand, requires about 40 watts of power and a small fuel cell cannot provide enough output to sustain the demand. The system needs a battery as back up. In essence, the fuel cell becomes a slave to the battery and serves more like a charger. The same applies to a fuel cell-powered cell phones and cameras (Sony VGN-FZ11S battery).

The fuel cell has not seen the same earth-shattering breakthroughs that microelectronics has enjoyed. The Moore's laws don't apply here. The continued struggle is low power, large size, premature aging and high cost. There are also transportation issues that inhibit passengers from bringing fuel on an aircraft. These rules will likely change in the next two years. The ICAO dangerous goods panel (DGP) has already established an exclusion to allow the transport and operation of methanol fuel cells on commercial flights. This same standard will not yet apply to storage of hydrogen gas, however (Toshiba PA3535U-1BRS battery).

When examining alternative power sources, the traditional battery starts to look awfully good. It is small, clean, quiet and provides an instant source of high power when needed. Similar to the combustion engine in a car, the battery is hard to replace with something that offers equivalent energy density and is affordable (Toshiba PA3534U-1BRS battery). An inexhaustible fuel cell would be nice, but for now we are beholden to the old-fashioned electrochemical concept, called a battery. There are no major developments on the horizon that will change the way we use portable equipment and atomic fusion as a potential portable power source hasn't entered the race yet. It is our hope, however, that the fuel cell will succeed as a clean energy source for our future generations (Toshiba PA3399U-2BRS battery).

Non-Correctable Battery Problems

Some rechargeable batteries can be restored through external means, such as applying a full discharge. There are, however, many defects that cannot be corrected. These include high internal resistance, elevated self-discharge, electrical short, dry-out, plate corrosion and general chemical breakdown (Sony VGN-FZ29VN battery).

The performance loss of a battery occurs naturally as part of usage and aging; some is hastened by lack of maintenance, harsh field conditions and poor charging practices. This paper examines the cause of non-correctable battery problems and explores ways to minimize these breakdowns(Sony VGN-FZ290 battery).

High Self-discharge
All batteries are affected by self-discharge. This is not a defect per se, although improper use enhances the condition. Self-discharge is asymptotical; the highest loss occurs right after charge, and then tapers off(Sony VGP-BPL7 battery).

Nickel-based batteries exhibit a relatively high self-discharge. At ambient temperature, a new nickel-cadmium loses about 10% of its capacity in the first 24 hours after charge. The self-discharge settles to about 10% per month afterwards. Higher temperature increases the self-discharge substantially. As a general guideline, the rate of self-discharge doubles with every 10°C (18°F) increase in temperature. The self-discharge of nickel-metal-hydride is about 30% higher than that of nickel-cadmium(Sony VGP-BPL12 battery).

The self-discharge increases after a nickel-based battery has been cycled for a few hundred times. The battery plates begin to swell and press more firmly against the separator. Metallic dendrites, which are the result of crystalline formation (memory), also increase the self-discharge by marring the separator. Discard a nickel-based battery if the self-discharge reaches 30% in 24 hours(Sony VGP-BPS12 battery).

The self-discharge of the lithium-ion battery is 5% in the first 24 hours after charge, and then reduces to 1% to 2% per month thereafter. The safety circuit adds about 3%. High cycle count and aging have little effect on the self-discharge of lithium-based batteries.
A lead-acid battery self-discharges at only 5% per month or 50% per year. Repeated deep cycling increases self-discharge(Sony VGP-BPS15 battery).

The percentage of self-discharge can be measured with a battery analyzer but the procedure takes several hours. Elevated internal battery resistance often reflects in higher internal battery resistance, a parameter that can be measured with an impedance meter or the OhmTest program of the Cadex battery analyzers(Sony VGP-BPS18 battery).
Cell matching
Even with modern manufacturing techniques, the cell capacities cannot be accurately predicted, especially with nickel-based cells. As part of manufacturing, each cell is measured and segregated into categories according to their inherent capacity levels. The high capacity 'A' cells are commonly sold for special applications at premium prices; the mid-range 'B' cells are used for commercial and industrial applications; and the low-end 'C' cells are sold at bargain prices. Cycling will not significantly improve the capacity of the low-end cells. When purchasing rechargeable batteries at a reduced price, the buyer should be prepared to accept lower capacity levels(Sony VGN-FZ17 battery).

The cells in a pack should be matched within +/- 2.5%. Tighter tolerances are required on batteries with high cell count, those delivering high load currents and packs operating at cold temperatures. If only slightly off, the cells in a new pack will adapt to each other after a few charge/discharge cycles. There is a correlation between well-balanced cells and battery longevity(Sony VGN-FZ11S battery).

Why is cell matching so important? A weak cell holds less capacity and is discharged more quickly than the strong one. This imbalance may cause cell reversal on the weak cell if discharged too low. On charge, the weak cell is ready first and goes into heat-generating overcharge while the stronger cell still accepts charge and remains cool. In both cases, the weak cell is at a disadvantage, making it even weaker and contributing to a more acute cell mismatch(Sony VGN-FZ17L battery).

Quality cells are more consistent in capacity and age more evenly than the lower quality counterparts. Manufacturers of high-end power tools choose high quality cells because of durability under heavy load and temperature extremes. The extra cost pays back on longer lasting packs(Sony VGN-FZ31E battery).

lithium-based cells are by nature closely matched when they come off the manufacturing line. Tight tolerances are important because all cells in a pack must reach the full-charge and end-of-discharge voltage thresholds at a unified time. A built-in protection circuit safeguards against cells that do not follow a normal voltage pattern(Sony VGN-FZ61B battery).

Shorted Cells
Manufacturers are often unable to explain why some cells develop high electrical leakage or an electrical short while still relatively new. The suspected culprit is foreign particles that contaminate the cells during manufacturing. Another possible cause is rough spots on the plates that damage the separator. Better manufacturing processes have reduced the 'infant mortality' rate significantly(Sony Vaio VGN-FZ18M battery).

Cell reversal caused by deep discharging also contributes to shorted cells. This may occur if a nickel-based battery is being fully depleted under a heavy load. nickel-cadmium is designed with some reverse voltage protection. A high reverse current, however, will produce a permanent electrical short. Another contributor is marring of the separator through uncontrolled crystalline formation, also known as memory(Sony VGN-FZ150E battery).

Applying momentary high-current bursts in an attempt to repair shorted cells offers limited success. The short may temporarily evaporate but the damage to the separator material remains. The repaired cell often exhibits a high self-discharge and the short frequently returns. Replacing a shorted cell in an aging pack is not recommended unless the new cell is matched with the others in terms of voltage and capacity(Sony VGN-FZ460E battery).
Loss of Electrolyte
Although sealed, the cells may lose some electrolyte during their life, especially if venting occurs due to excessive pressure during careless charging. Once venting has occurred, the spring-loaded vent seal on nickel-based cells may never properly close again, resulting in a build-up of white powder around the seal opening. The loss of electrolyte will eventually lower the battery capacity(Sony VGP-BPS9 battery).

Permeation, or loss of electrolyte in valve regulated lead-acid batteries (VRLA) is a recurring problem. Overcharging and operating at high temperatures are the causes. Replenishing lost liquid by adding water offers limited success. Although some capacity may be regained, the performance becomes unreliable(Sony VGP-BPS8 battery).

If correctly charged, lithium-ion cell should never generate gases and cause venting. But in spite of what is said, the lithium-based cells can build up internal pressure under certain conditions. Some cells include an electrical switch that disconnects the current flow if the cell pressure reaches a critical level. Other cells rupture a membrane to release the gases in a controlled way. lithium-ion-polymer in a pouch cell sometime grows to the shape of a small balloon because these cells do not include venting. Ballooning cell are known to damage the housing of the portable device(Sony Vaio VGN-FZ battery).