AA and AAA Rechargeable Batteries
Disposable alkaline AA and AAA batteries are being replaced by rechargeable AA and AAA batteries both for their environmental and financial advantages. Rechargeable batteries come in standard battery sizes and have much higher capacity than the classic alkaline batteries.
There are several types of rechargeable batteries available in sizes AA and AAA which use different combination of chemicals. The most popular are the following types:
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NiCd (nickel cadmium) battery uses nickel oxide hydroxide and metallic cadmium as electrodes. It maintains constant voltage as it discharges and can be charged up to 1000 times. One of the biggest disadvantages of NiCd batteries is the memory effect if repeatedly charged after being only partly discharged. The reason for memory effect in NiCd batteries is formation of small crystals which lower the voltage at each recharge making the battery eventually useless.
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NiMH (nickel-meral hydride cell) battery has similar discharge rate than NiCd battery but up to three times higher capacity than NiCd battery of the same size. One of the greatest advantages of NiMH batteries is also lack of memory effect and price comparable to NiCd batteries. However, NiMH batteries have relatively high self-discharge rate which is 5-10% on the first day. Since 2005 are also available low self-discharge NiMH batteries which according to the manufacturers retain 70-85% of their capacity after one year if being stored at 20 degrees Celsius (68 degrees Fahrenheit).
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Lately have become very popular also Lithium-ion batteries mostly due to low self-discharge rate when not being used. However, Lithium-ion batteries do not come in standard AA and AAA sizes and are more expensive than NiMH and NiCd batteries.