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.

Available since early 1950, the NiCd continues to be the most commonly used portable battery today. It is rated at 1.2 volts per cell. It provides good load characteristics, is economically priced, simple to use and forgiving if abused. The main applications are mobile phones, portable radios, video cameras, power tools and biomedical instruments. The NiCd has medium energy density and needs regular exercise (full discharge/full charge cycling) to prevent so called "memory buildup". With proper care, the NiCd can provide up to 1500 discharge/charge cycles. At an estimated 6 cents per cycle, the NiCd is the most economical battery available.

Introduced in the seventies and commercially available in the early nineties, the NiMH offers 30% higher energy density than the NiCd. The main applications are mobile phones and notebook computers where high-energy is of importance, regular exercising is not practical and cost is secondary. It is rated at 1.2 volts per cell. The NiMH does not perform as well when a high current load is applied (e.g. power tools). In addition, its self-discharge rate is highest among rechargeable batteries. The NiMH provides up to 500 charge/discharge cycles at an estimated cost of 14 cents per cycle. Because of the high current demand during radio transmission and the battery’s limited cycle count, the NiMH has been less than satisfactory for portable two-way radios.

New on the market and in growing supply, the Li-ion provides twice the energy density of the NiCd and has the lowest self discharge rate among rechargeable batteries. It is rated at 3.6 volts per cell. For safety and longevity reasons, each battery pack must contain a control circuit to limit the voltage peak and minimum during charge and discharge and it should not be charged on a NiCd or NiMH charger. Typical applications are for notebook computers, mobile phones and now portable radios! The charge time is 3 to 6 hours and the cycle count is 300 to 500. The load characteristic is better than a NiMH and SLA but not as good as the NiCd. The Li-ion is currently expensive with an operational cost at 30 cents per cycle. The cost is expected to drop with higher volume manufacturing and replacement of the current cobalt element with other chemistry. The Li-ion battery should be treated with care, as it is very volatile, highly flammable and difficult to extinguish when alight. The technical literature suggests that they have a life of two years from date of manufacturer!