Patent ID: 7553581

Claim:
A sealed prismatic battery, comprising: a battery casing having a cylindrically shaped body with a bottom part and an upper opening, the upper opening having a laterally long shape in which the back-and-forth width dimension is smaller than the lateral length dimension; and a lid which fits in the upper opening of the battery casing, the lid having a laterally long shape in which the back-and-forth width dimension is smaller than the lateral length, and having no thin part and the outer periphery of the lid being welded to the periphery of the upper opening to form a welded portion; wherein the welded portion includes a pair of fragile parts having low weld strength disposed in two long sides of the welded portion and formed at the ends of said two long sides of the welded portion which are parallel to each other, respectively, and wherein the pair of the fragile parts is diagonally positioned on the upper face of the battery casing, and wherein the ends of two long sides include not only the places where the two long sides of the welded portion cross two short sides of the welded portion but also places which extend from the places where the long sides cross the short sides toward the center of the long sides by 10% of the length dimension of the long sides, and wherein a ratio of a length dimension of the fragile part to a length dimension of the long side is in a range of 15 to 50%, and wherein the two short sides of the weld portion are linear or have a circular arc configuration.