We report an outstanding electrochemical performance of a gel type lithium ion battery with long cycle life enabled by a dense transparent polymeric single ion conductor. The polymer electrolyte was synthesized by a side chain grafting method with 4-amino-4’-trifluoromethyl bis(benzene sulfonyl)imide grafted on side chains of poly(ethylene-alt-maleic anhydride) with a grafting ratio of 50%. Blending lithiated iononmers with poly(vinylidene fluoride-co-hexafluoropropylene) via a solution cast method results in a dense transparent film. The fabricated blend polymer electrolyte film has an ionic conductivity of 0.104 mS cm−1 at room temperature, a tensile strength of 15.5 MPa and percent elongation at break of 5%. A gel type single ion conductive polymeric lithium ion battery was assembled using the blend film as the separator as well as the electrolyte, LiFePO4/C mixed with ionomers as the cathode and a lithium foil as the anode. The battery delivers a reversible discharge capacity of 100 mAh g−1 at 1 C under room temperature for 1000 cycles without obvious decay. The stable cyclic imide and comb-like structure of the polymer is largely responsible for the excellent battery performance. The side chain grafted single ion conducting polymer electrolyte is well suited for large-scale production.