Elastomers consisting of a copolymer of epichlorohydrin and ethylene oxide were studied as solid polymer electrolytes in polymer/KOH systems. This alkaline solid polymer electrolyte exhibits a high ionic conductivity at room temperature, typically 10−3 S cm−1, as measured by electrochemical impedance spectroscopy. Moreover, it exhibits a good anionic transference number, namely 0.93, as determined by a technique derived from the Hittorf method. The potential stability window (0.9 V) has been determined by cyclic voltammetry. Initial tests concerning a nickel/metal hydride secondary battery and a zinc/air primary cell, containing this solid polymer electrolyte, show good performance of these systems in such electrolyte, at different temperatures.