Batteries

These are not normally used as a main power source for audio or video equipment, but are often used in auxiliary devices, e.g. remote wireless or infrared controllers, microphones, etc. There are many different chemical systems employed in these cells, some using very expensive components (Sony Vaio VGN-FZ battery) .

The requirement for, say, a clock battery, which will be expected to supply a comparatively low amount of energy for a year or so, is different than that required for a battery powering a digital camera with a flash lamp, which has to supply pulses of relatively high power (Sony VGP-BPS8 battery) .

Within many electronic devices, for example real time clock circuitry and memory maintenance circuitry, there is a requirement for primary cells which will supply a low amount of power for ten or so years.

A few advantages of primary cells are that they are easily available, at least in the standard consumer sizes, have a long shelf life and a high power density (Sony VGP-BPL9 battery) .

As an emergency backup, then it can be useful to have a battery pack which will take standard primary cells, but chose an easily available cell size, AA, C or D

Originally, (well, in my childhood days) most primary cells were of zinc-carbon construction (Sony VGP-BPL11 battery) .

A later development was zinc chloride which has a greater capacity, whereas now most primary cells are of alkaline construction. However, in some situations the high capacity of the alkaline cells can cause a hazard due to sparking on installation. For example, a standard alkaline Duracell D cell has a capacity of 18000mAh, and therefore Zinc based cells are still used in hazardous situations (Sony VGP-BPL15 battery) .

Later cell technologies include zinc air, which provide energy only when a protective seal is removed and they thus have a very defined operational life. Other chemistries include silver oxide, mercury, and a whole range of lithium based cells, such as lithium iron sulphide, lithium manganese dioxide and lithium thionyl chloride (Sony VGN-FZ460E battery) .

These cells are usually highly matched to a particular application, and give a saving in size and weight (but not usually cost) when compared with an alkaline cell of the same capacity (Sony VGP-BPS11 battery) .

Secondary Batteries.

These are the batteries that most of this article will be concerned with, and is the area that causes most energy supply problems, since we not only take energy from the cell, but have to replace it also, so the problems will be at least doubled (SONY VAIO VGN-FZ4000 Battery) .

I will only consider four types of secondary cell; lead acid gel, Nickel Cadmium (Ni-Cad or Ni-Cd), Nickel-Metal Hydride (Ni-MH), and lithium-ion (Li-ion) (Apple A1281 battery) .

Lead Acid Gel Batteries

These are my preferred batteries, for the following reasons: Easily recharged with constant current or constant voltage system. The same cell can be used for fast cycling or long term float applications. Low internal impedance allows very high discharge currents. Excellent mechanical and vibrational strength (Apple A1189 battery) .

Absolutely no 'memory' effects, so can be recharged at any state of discharge. No damage due to cell reversal. 2V per cell, meaning fewer cells for lower battery cost and higher reliability. Cells can be paralleled for additional capacity. Construction allows air transportation without restrictions, and they are allowed in every country （Apple A1148 battery) .

They have an easily monitored capacity, since they have a gently sloping discharge voltage/time curve. Their operational voltage range -65 deg C to +65 degC is excellent, and they are readily available in rectangular format in 6, 12 or 24V packs. They give a very reliable and predictable performance at a low cost (HP PAVILION DV9700t Battery) .

They also have a long charge cycle life - up to 2000 cycles or eight years on float charge. Always store them in a fully charged condition, and check every month or so and top up their charge. They will self discharge at about 3% per month (HP PAVILION DV2 Battery) .

You won't like them because they are heavy (see example below to see how wrong you are!!). You will also forget to check their charge condition if not using them for a period of time (Dell INSPIRON 1420 Battery) .

Let us look at the Yuasa NP7-12 battery in more detail. This 12V battery has a capacity of 7.0Ah - that is at a 20 hour rate of 350mA to 10.5V. At a one hour rate of 4200mA then it has a capacity of 4.2Ah to an end voltage of 9.6V. The maximum discharge current with the standard spade terminals is 40A, and it has a charge retention of 85% over 6 months (Dell Inspiron E1505 Battery) .

It is in a robust plastic case about 151mm by 65mm by 98mm high, although it may be used in any position. It weighs 2.65Kg. Retails at about £15.00. A suitable constant current mains charger is readily available for £20.00, but it is feasible to use an even cheaper wall block type device at 0.1C for overnight charging (Dell Latitude D620 Battery) .

Now, if we try and make up a similar capacity Ni-Cad pack, we need 10 cells, since each is 1.2V. We will require a case and we will also need to do some wiring to connect the cells in series. A suitable 7Ah Ni-Cad cell is 33mm diam x 91mm high, and weighs 230gms at a retail price of about £9.50 each (Dell INSPIRON 1525 Battery) .

If we mount them in a block, as two rows of five, then we end up with a pack 91mm high by 66mm wide by 165mm long. This will be larger than the lead acid battery with the same rating when we put a rigid case around it. The total weight will be at least 2.3Kg, since we must be add wiring and the weight of the case. A decent charger/discharger may well cost £100 or so, the assembled battery pack in a case is likely to cost £150.00 (Dell Inspiron 6400 battery) .

Nickel Cadmium Batteries

Bearing in mind my list of advantages for lead acid batteries, why use Ni-Cads? The lead based storage battery was invented in 1859 (about ten years before the first dry cell), and it was about 100 years later that the sealed gel type lead acid battery was perfected (Toshiba PA3535U-1BRS battery) .

The Nickel Cadmium storage cell was invented in 1899, and it was not until the early 1960's that the sealed Ni-Cad cell started to be used, although the first sealed unit was developed in 1947. Well, historically the sealed devices seemed to appear at about the same time (IBM ThinkPad R50 battery) ,

so we can not say that one is more popular than the other because of tradition, but lead acid batteries have existed for a long time in their liquid form, and they were, and still are used for heavy power requirements, and I believe that is why lead acid gel batteries are not more popular for AV users - it is not being marketed into the AV area (COMPAQ Presario R3000 Battery) .

Most Ni-Cad cells are available as size for size replacements for the common consumer and industrial sized primary cells, and the cell voltage at 1.2V and a pretty level 1.2V at that, is comparable with the 1.5V of most primary cells (ASUS Eee PC 1000HE Battery ) .

Lead acid, at 2V, just does not have this market, so they are not made in the smaller sizes, and if we were using four lead acid cells to replace four primary cells, then we would have a serious over voltage problem. That, I believe is the commercial reason, but what about the technical reason for Ni-Cad's popularity (ASUS Eee PC 900 Battery) .

The major advantage of Ni-Cads is that the discharge voltage is constant, until it reaches a knee point at the end of the discharge cycle, when it rapidly falls. For many electrical/electronic devices in the 1960's, then if you had a consistent 6V supply, say, from 5 Ni-Cad cells, then an amplifier would perform just as well after one hour's use as at the beginning (ACER Aspire 3020 Battery) .

Electronics were relatively expensive, and it was unnecessary to have voltage regulators if you used Ni-Cad batteries. With lead acid gel batteries, then the amplifier performance may not be as good after one hour, but it would never suddenly fail (Dell Inspiron 6000 battery) .

Where a constant voltage was required, then regulators were necessary if using lead acid batteries, adding more cost to the device. The early regulators were also not very efficient, the excess power being mainly dumped as heat (Toshiba PA3399U-2BAS Battery) .

One problem with Ni-Cads, is the so called 'memory effect'. Many manufacturers have improved their batteries and now better understand this phenomenon.