sentences:  The Nickel–hydrogen battery was patented on February 25, 1971 by Alexandr Ilich Kloss and Boris Ioselevich Tsenter in the United States.NiH2 cells using 26% potassium hydroxide (KOH) as an electrolyte have shown a service life of 15 years or more at 80% depth of discharge (DOD)
  The energy density is 75 Wh/kg, 60 Wh/dm3 specific power 220 W/kg.The open-circuit voltage is 1.55 V, the average voltage during discharge is 1.25 V.
  
  While the energy density is only around one third as that of a lithium battery, the distinctive virtue of the nickel–hydrogen battery is its long life