Nickel-cadmium battery

Nickel-cadmium batteries (commonly abbreviated NiCd or NiCad) are a type of rechargeable battery first developed in 1961. They are commonly used in many portable electronic devices.

Nickel-cadmium cells have a nominal cell voltage of 1.2V and can supply high surge currents. This makes them a favourable choice for remote controlled electric toy aeroplanes, boats and cars.

NiCd batteries contain a nickel hydroxide positive electrode plate, a cadmium hydroxide negative electrode plate, a separator, and an alkaline electrolyte. NiCd batteries usually have a metal case with a sealing plate equipped with a self-sealing safety valve. The positive and negative electrode plates, isolated from each other by the separator, are rolled in a spiral shape inside the case.

The chemical reaction which occurs in a NiCd battery is:

This reaction goes from left to right when the battery is being discharged and from right to left when it is being recharged. The alkaline electrolyte (commonly KOH) is not consumed in this reaction.

It is often claimed that NiCd batteries suffer from a so-called "memory effect" if they are recharged before they have been fully discharged; the apparent symptom is that subsequent discharging will not be able to get as much power out of the battery. To address this apparent problem, NiCd battery chargers sometimes include the ability to fully discharge batteries before beginning recharging as a result. Never, however, discharge rechargeable batteries to zero voltage.

Similarly, "lazy battery effect" (sometimes used as a synonym for "memory effect") is used to describe the result of repeated overcharging; the symptom is that the battery appears to be fully charged but discharges quickly after only a brief period of operation. Sometimes, much of the lost capacity can be recovered by a few deep discharge cycles. If treated well, NiCd batteries can last for 1000 cycles or more before capacity drops below 50% of original.

The self discharge rate for NiCd rechargeables ranges around 20% per month and is considerably less than that of Nickel metal hydride batteries which is around 30% per month. The self discharge rate is highest for full charge state and drops off somewhat for lower charge states. It is sometimes recommended that NiCd Batteries be charged to around 40% capacity for long-term storage.

NiCd batteries contain cadmium, which is a toxic heavy metal and therefore requires special care when the batteries are disposed of. Nickel metal hydride batteries are similar to NiCd, but less toxic.