NiCad and NiMH Battery Pack Systems

A Nickel-Metal Hydride cell, abbreviated NiMH, is a type of secondary electrochemical cell that uses a hydrogen-absorbing alloy for the negative electrode instead of cadmium. As in NiCd cells, the positive electrode is nickel oxyhydroxide (NiOOH). A NiMH cell can have two to three times the capacity of an equivalent size nickel-cadmium battery. However, compared to the lithium-ion cell, the volumetric energy density is lower and self-discharge is higher.

Useful discharge capacity is a decreasing function of the discharge rate, but up to a rate of around 1×C (full discharge in one hour) it does not differ significantly from the nominal capacity.

The specific energy density for NiMH material is approximately 70 W•h/kg (250 kJ/kg), with a volumetric energy density of about 300 W•h/L (360 MJ/m3).