Non-aqueous gel polymer electrolytes (GPEs) consisting of 30% poly(methyl methacrylate)-grafted natural rubber (MG30), lithium triflate (LiTf), and ethylene carbonate (EC) dissolved in tetrahydrofuran are examined as electrolytes for lithium polymer batteries. The AC impedance technique is employed at room and elevated temperatures in the frequency range between 0.1 kHz and 1.0 MHz to optimize the conductivity of MG30–LiTf samples. The membrane containing 35 wt.% of LiTf is found to exhibit the highest ionic conductivity. The introduction of EC resulted in increased ionic conductivity of up to 8.95 × 10−3 S cm−1 at room temperature for the composition MG30(15):LiTf(9):EC(76). The temperature dependence conductivity for all systems studied is of the Vogel–Tamman–Fulcher type. Attenuated total reflectance-Fourier transformed infrared spectroscopic analysis suggested that EC penetrated between the polymer chains without perturbing the complexation that occurred between the polymer and lithium salt. The Li/Li+ interface stability is established to withstand voltages greater than 4.2 V. A lithium polymer half-cell is successfully fabricated using MG30-based GPE and the cell with configuration of Li/MG30:LiTf:EC/LiCoO2 is found to show good cycling efficiency at room temperature.