Over 40% of all rechargeable batteries sold today are Nickel Cadmium (NiCd) but with the rapid development of more sophisticated appliances requiring portable batteries, other battery chemistry technologies are being used and there are more in development. It takes many years for a new battery chemistry to be developed and fully tested before manufacturers will design their products to suit the new batteries.

New battery chemistries are often evaluated in terms of energy density alone (i.e. size vs. storage capacity). Operational costs, load characteristics, self-discharge and exercise requirements are of equal importance when selecting a battery. Each battery chemistry type has its own distinctive differences and application use.

This is the most common portable battery chemistry in use today. It provides good load characteristics, is economically priced and simple to use. You'll find them in batteries for power tools, mobile phones, two way radios, video cameras and medical instruments. They are most suitable for driving appliances with motors where heavy amperage loads are needed. With proper use and care they provide up to 1500 charge/discharge cycles.

The most annoying feature of this Nickel/Cadmium chemistry is that it builds up a "memory" problem (a crystalline formation) if not regularly discharged when in use. This feature is apparent if the NiCd battery is continually "topped up". Reduction of the "memory" is achieved by the discharging of the battery.

The major Japanese manufacturers claim to have reduced this "memory" problem in the technology, to some degree.

The Cadmium content of the NiCd battery is toxic and is hazardous to the environment. Governments are slowly moving towards responsible disposal programmes to reduce the hazard.

The NiMH battery is becoming more widely used as the chemistry technology has improved and the costs of production have come down. You'll find them increasingly in use in mobile phones, laptop computers, video cameras and two way radios where large amperage loads are not required. The NiMH battery is appealing to battery manufacturers as it has about 30% more capacity, size-wise, than NiCd.

Less appealing is that NiMH batteries only provide around 500 charge/discharge cycles - however there is very little in the way of "memory" problems. This battery can be regularly "topped up" and need only be fully discharged every month or so. NiMH chemistry is not regarded as being hazardous to the environment.

This battery is also known as the Gelcell battery. It is "sealed" and contains lead plates and acid "gel" just like a car battery. (There is no requirement to "top it up" with distilled water).

It is heavy and commonly used where bulk power is required, weight or size is not critical and cost must be low.

Applications are in Uninterrupted Power Supply units, "bag phones", emergency lighting, alarm backup systems, wheel chairs and portable hospital equipment. It has no "memory" problems but it must be regularly charged (topped up) to maintain good charge acceptance. It has a charge/discharge life of 200 to 300 cycles. The Lead content makes the battery hazardous to the environment.

New on the market and growing in use for low amperage appliances like mobile phones, laptop computers and video cameras where size is important (each cell has a large capacity, size-wise, and is three times the voltage of the above battery chemistries). These batteries are very expensive as each one contains a control circuit to limit the voltage peak during charging. It cannot be charged on a NiCd or NiMH charger. It has a low charge/discharge life of 300 to 500 cycles.

The Li-ion battery has no "memory" problems and can be charged at any time. The high cost of production is expected to drop with volume manufacturing and with the substitution of the current cobalt element of the chemistry.

Each battery should be treated with care as it is very volatile, highly inflammable and difficult to extinguish when alight - like magnesium. It is not regarded as hazardous to the environment.

The technical literature suggests that it has a life of two years from "date of manufacture"!

Very new on the market and being promoted to the public as a money saving alternative to the "torch battery". It is rated at 1.5volts per cell. It has a very low and almost unnoticeable self-discharge rate but does not operate well in low temperatures below 0 degrees C. The battery is not designed to carry heavy load. The absolute cycle life of this battery is very low at around 10 cycles before it just gives up. This low cycle life makes it the most expensive rechargeable battery cell on the market with an operational cost at 75 cents per cycle. This battery does not have any "memory" problems.

Mass production has commenced of this latest technology ultra-slim battery cell in a prismatic shape (non-cylindrical). This new battery has a similar life to Li-ion cells at around 500 cycles. Its slimness and light weight makes it ideal for applications such as mobile phones and computer laptop batteries where space and weight is paramount in design. The cells are constructed from a flexible, multi-layered 100 micron thick film that does not require a hard leak-proof case The laminate has five layers; a current collecting metal foil, cathode, electrolyte, lithium foil anode and an insulator.