A secondary battery includes an electrode unit having a first electrode plate, a second electrode plate, a separator interposed therebetween, and first and second electrode tabs respectively extending from the first and second electrode plates, a can adapted to accommodate the electrode unit and an electrolytic solution, and a cap plate adapted to seal the can and having an electrolytic solution inlet, wherein the electrolytic solution inlet has an area on one surface of the cap plate different from that on another surface of the cap plate.