Nickel–metal hydride battery
Modern Ni–MH rechargeable cells | |
| Specific energy | 0.22-0.43 MJ/kg (60–120 W·h/kg) |
|---|---|
| Energy density | 140–300 W·h/L |
| Specific power | 250–1,000 W/kg |
| Charge/discharge efficiency | 66%–92% |
| Self-discharge rate | Per month:
|
| Cycle durability | 180–2000 cycles |
| Nominal cell voltage | 1.2 V |
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. They provide a cell voltage of about 1.2V while fresh alkaline cells provide 1.5V; however devices designed for alkaline batteries operate until cell voltage gradually drops to around 1.0V, while the voltage of a fully-charged NiMH cell drops more slowly, giving good endurance for a 1.0V end point. NiMH batteries are less prone to leaking corrosive electrolyte than primary batteries.