NiMH Nickel Metal Hydride Battery Self Discharge

- details about NiMH battery self discharge and how this affects their performance.

One issue that is an issue with many forms of cell and battery is that of self discharge.

While all cells suffer from some level, NiMH self discharge is a particular issue because the level is higher than many other forms of cell.

NiMH battery self-discharge

One of the problems with NiMH cells is that they self-discharge over a relatively short period of time. All cells will lose their charge over time, even if they are not used, but this is a particular problem for NiMH cells.

Typically it might be expected that a fully charged cell might self-discharge over a period of a few weeks. NiCds are better than NiMH cells but in turn they not as good as normal primary cells but NiCds will typically retain charge over several months dependent upon the type of battery or cell.

There are several factors that contribute to the self-discharge of an NiMH cell dependent upon the state of charge. These can broadly be described as an oxygen cycle that occurs at high states of charge, and then ion movement that contributes to the self-discharge over longer periods of time.

One important factor in the rate of self-discharge is the temperature at which the cell is held. It is found that at higher temperatures, the rate of discharge significantly increases. Therefore cells should be kept cool if it is necessary for them to hold their charge over longer periods.

By Ian Poole

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