A battery comprises an anode, a cathode, and a polymer electrolyte disposed between the anode and the cathode. The polymer electrolyte can include an inert hydrophilic polymer matrix impregnated with an aqueous electrolyte. The hydrophilic polymer matrix can include a polar vinyl monomer, an initiator, and a cross-linker. A gassing inhibitor can be included in the polymer electrolyte to help avoid issues with overcharging of the electrodes.