In the present study, polymer electrolyte with poly(vinyl alcohol) (PVA) blended with cellulose acetate (CA) was chosen to prepare composite electrolyte using ammonium triflate salt and nano sized alumina (Al2O3- < 50 nm) by the solution casting method. The as prepared samples were characterized by X-ray diffraction, FT-IR, differential scanning calorimetry and AC impedance spectra. The loss tangent and dielectric studies were carried out for all the prepared samples using AC impedance analysis. Activation energy with regression values and relaxation time were calculated and found to be low for the highest conducting membranes. The presence of 0.1 mol content of nano alumina has enhanced the ionic conductivity significantly to the value of 2.012 × 10-3 S/cm from that of the filler-free electrolyte (2.93 × 10-4 S/cm). Ionic transference number was calculated by electrostatic polarization method and it was found to be 0.9684, which shows the conducting species were ions. A proton battery fabricated using the configuration Zn+ZnSO4. H2O || PVA-CA-0.5 mol NH4CF3SO3-0.1 mol Al2O3 || PbO2 + V2O5 produced a steady state open circuit voltage of 1.39 V, which proves the prepared composite electrolyte is suitable solid electrolyte for electrochemical devices.