A Nickel-metal hydride (NiMH) battery is a type of rechargeable battery that uses nickel oxide hydroxide at the positive electrode and a hydrogen-absorbing alloy at the negative electrode. These batteries have two to three times the capacity of nickel-cadmium (NiCd) batteries of the same size and significantly higher energy density, although only half of lithium-ion batteries. NiMH batteries are environmentally friendly, containing only mildly toxic substances and being recyclable. They have replaced NiCd batteries for many roles, notably small rechargeable batteries, and are commonly available in AA (penlight-size) batteries.
NiMH batteries are well suited for devices that require large amounts of energy and are used frequently, such as digital cameras, GPS units, and MP3 players. They have a greater service advantage over other primary battery types at low temperature extremes, operating at -20°C. NiMH batteries have a double energy density compared to lead-acid batteries, are harmless for the environment, recyclable, and resistant to overcharge and over-discharge. However, they have a relatively shorter lifetime of around 200 to 300 cycles if discharged rapidly on high loads.
Compared to lithium-ion batteries, NiMH batteries are much lower in cost, require very little maintenance, are more environmentally friendly, and are free from transportation regulations that Li-ion batteries must follow when being shipped. However, they have different charging needs and are much harder to charge than Li-ion batteries because they dont have a "float charge" voltage like lithium-ion chemistry.
In summary, NiMH batteries are a popular choice for various portable electronic devices due to their high capacity, energy density, and environmental friendliness, despite having a shorter lifetime compared to some other battery types.
