Nickel–metal hydride battery

A nickel–metal hydride battery (NiMH or Ni–MH) is a type of rechargeable battery. The chemical reaction at the positive electrode is similar to that of the older nickel–cadmium cell (NiCd), with both using nickel oxide hydroxide, NiO(OH). However, the negative electrodes use a hydrogen-absorbing alloy instead of cadmium. NiMH batteries typically have two to three times the capacity of NiCd batteries of the same size, with significantly higher energy density, although only about half that of lithium-ion batteries. NiMH batteries have almost entirely replaced NiCd.

These batteries are typically used as a substitute for similarly shaped non-rechargeable alkaline and other primary batteries. While they provide a cell voltage of about 1.2V and fresh alkaline cells provide 1.5V, most devices designed for alkaline batteries can generally operate until cell voltage drops to around 1.0V. Since the voltage of a fully-charged NiMH cell drops more slowly than an alkaline cell, it will provide similar endurance for a 1.0V end point. NiMH batteries are less prone to leaking corrosive electrolyte than primary batteries.