Hybrid solid polymer electrolyte films consisting of poly(vinyl alcohol) (PVA), poly(methyl methacrylate) (PMMA), LiBF4, and ethylene carbonate/propylene carbonate (EC/PC) were prepared with a solvent-casting technique. The complexation was investigated with Fourier transform infrared and X-ray diffraction. The ionic conductivities of the electrolyte films were determined with an alternating-current impedance technique for various temperatures in the range of 302-373 K. The maximum conductivity value, 1.2886 x 10(-3) S/cm, was observed for a PVA-PMMA-LiBF4-EC complex. Thermogravimetry/differential thermal analysis was performed to ascertain the thermal stability of the electrolyte with the maximum conductivity value. For an examination of the cyclic and reversible performance of the film, a cyclic voltammetry study was carried out. The surface morphology of the EC- and PC-based electrolytes was examined with scanning electron microscopy. (C) 2003 Wiley Periodicals, Inc.