A nickel–hydrogen battery (NiH₂ or Ni–H₂) is a rechargeable electrochemical power source based on nickel and hydrogen. It differs from a nickel–metal hydride (NIMH) battery by the use of hydrogen in gaseous form, stored in a pressurized cell at up to 1200 psi (82.7 bar) pressure. The Nickel-hydrogen battery was patented on Feb 25, 1971 by Alexandr Ilich Kloss and Boris Ioselevich Tsenter in the United States.