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 in the United States on February 25, 1971 by Alexandr Ilich Kloss, Vyacheslav Mikhailovic Sergeev and Boris Ioselevich Tsenter from the Soviet Union.