Classical solution-cast and ultrasonic-microwave-irradiated solution-cast methods have been used for the preparation of solid polymer electrolyte (SPE) films comprising polymer matrix of poly(ethylene oxide) and poly(methyl methacrylate) blend and lithium tetrafluoroborate (LiBF4) ionic salt. These films have been characterized by employing the X-ray diffraction, Fourier transform infrared spectroscopy, dielectric relaxation spectroscopy, and electrochemical analyser. It is observed that the temperature-dependent ionic conductivity of these predominantly amorphous solid ion-dipolar complexes is governed by their dielectric permittivity and the relaxation times of various dynamical processes. The relaxation times and the dc ionic conductivity of these electrolyte materials obey the Arrhenius behaviour, whereas the normalized ac conductivity exhibits the time-temperature superposition scaling. The influence of sample preparation methods on the performance of SPE films and the suitability of these materials for the lithium-ion batteries has been explored by noting the relative changes in their structural, dielectric, electrical, ionic conductivity, and the electrochemical parameters.