This paper describes the synthesis and characterization of a new solid acid polymer electrolyte (SAPE) based on polyvinyl alcohol, lithium bromide and sulfuric acid. Ethylene carbonate was used as plasticizer in the matrix for membranes prepared by a solution cast technique. AC impedance spectroscopy was used to determine the ionic conductivity of SAPE at different temperature and frequency values giving some insight into its potential utility as a solid acid membrane in solid state batteries. The ionic transference number of mobile ions has been estimated by a dc polarization method and the results reveal that the conducting species are predominately ions. A solid state magnesium battery is fabricated and characterized. A cell with the configuration Mg/SAPE/MnO2 gives a capacity of 270 mAh/g and has an internal resistance approximate to 175 Omega. The electrode degradation after discharge was characterized by XRD analysis. (C) 2009 Elsevier B.V. All rights reserved.