Abstract Poly(methyl methacrylate), PMMA based gel polymer electrolytes (GPE) containing immobilized lithium bis(oxalato)borate, C4BO8Li or LiBOB dissolved in a propylene carbonate–ethylene carbonate binary solvent were prepared by heating the cast solution between 70 and 80°C for 20min. The electrolyte composition with 5wt.% PMMA exhibited the highest conductivity of 3.27 and 7.46mScm−1 at 298 and 343K respectively. Cyclic voltammetry studies on the GPE containing 15wt.% PMMA and 85wt.% (0.6M LiBOB) dissolved in equal weight of ethylene and propylene carbonates showed that the electrochemical potential stability window of the electrolyte lies in the range between −1.7 to +1.7V. Linear sweep voltammetry indicates the gel polymer electrolyte is stable up to 1.7V. The electrical double layer capacitor (EDLC) using the highest conducting GPE and activated carbon derived from shells of the mata kucing (Dimocarpus longan) fruit has capacitance of ∼685mFg−1 on the first cycle. The EDLC performance was also characterized using cyclic voltammetry and charge–discharge processes at constant current.