Capacity retention characteristics of nickel/metal hydride (Ni/MH) batteries with polymer hydrogel electrolyte prepared from cross-linked potassium poly(acrylate) and a 7.3 M KOH aqueous solution were investigated. The experimental Ni/MH cell with the polymer hydrogel electrolyte exhibited much better capacity retention than that with a 7.3 M KOH aqueous solution at 25 degrees C. It was also found that the polymer hydrogel electrolyte suppressed both reversible and irreversible capacity losses. The effects were fairly remarkable at relatively high temperature, such as 55 degrees C. These characteristics of the polymer hydrogel electrolyte can be significant advantages for use in the practical Ni/MH batteries. (C) 2004 The Electrochemical Society.