Polymer electrolyte films of polyvinyl alcohol as host polymer, poly(3,4-etylenedioxythiophene)/ poly(styrenesulphonate), magnesium bromide were prepared using solution cast technique. Succinonitrile was used as plasticiser in the matrix at different concentrations. These films were characterised using thermogravimetric analysis, X-ray diffraction and ac impedance spectroscopy. The conductivity measurement was used to determine the ionic conductivity of the polymer electrolyte at different temperature and frequency values, giving some insight into its potential utility as a solid membrane in solid state batteries. The ionic transference number of mobile ions has been estimated by a dc polarisation method, and the results reveal that the conducting species are predominately ions. A solid state magnesium battery was fabricated and characterised.