The nickel–iron battery (NiFe battery) is a rechargeable battery having nickel(III) oxide-hydroxide positive plates and iron negative plates, with an electrolyte of potassium hydroxide. The active materials are held in nickel-plated steel tubes or perforated pockets. It is a very robust battery which is tolerant of abuse, (overcharge, overdischarge, and short-circuiting) and can have very long life even if so treated. The battery needs maintenance, as hydrogen builds up when (dis)charging. The C-rate can be higher than in other batteries, using up to C=5 only reduces capacity by about 10%.
Applications: short-term storage, arbitrage, distributed/off-grid storage, frequency or voltage regulation