NiMH cells historically had a somewhat higher self-discharge rate (equivalent to internal leakage) than NiCd cells.
The self-discharge rate is, for most applications, sufficiently low enough, but it is higher than in accumulators.
The beauty of this is, first of all, ultracapacitors have an extremely low self-discharge rate.
And I should also mention that it uses less power when it's idle, but still alive, than the battery's own self-discharge rate.
In both types of cell, the self-discharge rate is highest for a full charge state and drops off somewhat for lower charge states.
Common NiMH and NiCd rechargeable batteries have a high self-discharge rate, making them unsuitable for use in smoke detectors.
The self-discharge rate varies greatly with temperature, where lower storage temperature leads to slower discharge rate and longer battery life.
Corrosion of the insulators was found to be a problem in the harsh chemical environment as they gradually became conductive and the self-discharge rate increased.
Most button cell batteries are not rechargeable due to the inferior capacity and high self-discharge rate of rechargeable batteries.
The cells have the disadvantage of relatively high self-discharge rate, i.e chemical reduction of Ni(III) into Ni(II) in the cathode:
