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.

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"!

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.

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, computer laptop batteries, PDA's and IPod's 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.