Patent ID: 8338009

Claim:
A battery comprising: a battery case having an opening sealed with a sealing plate, wherein the sealing plate has a protrusion extending in a direction toward the outside of the battery case, a ring-shaped insulator is provided on an outer circumferential surface of the protrusion, an inner circumferential portion of the insulator is in contact with the outer circumferential surface of the protrusion, an outer circumferential portion of the insulator is extended to be positioned on an opening end of the battery case, said outer circumferential portion of the insulator being disposed over sidewalls of the battery case, the inner circumferential portion is fitted to part of the protrusion having the smallest outer diameter, an outer diameter of the protrusion decreases in a direction toward a bottom surface of the battery case, and the insulator has a thicker part extending from the inner circumferential portion toward the outer circumferential portion, an inner diameter of the thicker part decreases in the direction toward a bottom surface of the battery case, and an inner circumferential surface of the thicker part is in contact with the outer circumferential surface of the protrusion.