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A nickel-cadmium battery (NiCd or NiCad) is a rechargeable battery used for portable computers, drills, camcorders and other small battery-operated devices requiring an even power discharge. NiCds use electrodes made of nickel oxide hydroxide, metallic cadmium and an alkaline electrolyte of potassium hydroxide.
The NiCd battery was invented by Waldemar Junger and patented in 1899.
Two or more NiCd battery cells combine to form a battery pack. Because they are often sized like primary cells (non-rechargeable batteries), NiCds may have lower terminal voltage and less ampere-hour capacity. However, NiCds provide a nearly constant terminal voltage during discharge, unlike primary cells, which results in nearly undetectable low charges. During discharge, NiCd batteries transform chemical energy into electric energy. During recharge, NiCds retransform electric energy into chemical energy.
NiCd battery advantages are as follows:
NiCd batteries are extremely toxic. Additionally, nickel and cadmium are expensive metals.
Unlike lead-acid batteries, NiCd batteries heat excessively, go into thermal runaway mode and self-destruct if charged with a dynamo - even in over-current cutout systems. However, NiCd battery packs are usually equipped with an interior thermal charger cutoff, which is signaled if a battery heats and/or reaches maximum voltage.