Patent ID: 7754373

Claim:
A sealed prismatic battery comprising: a battery casing which is shaped like an oval quadrangle having a width in a direction of thickness smaller than a height in a longitudinal direction and a length in a lateral direction and in which side walls facing in the lateral direction swell outward in the lateral direction so as to form circular-arc shapes in general; and an opening vent which is provided in vicinity of ends of at least one of the side walls of the battery casing facing in the lateral direction, wherein the battery casing includes a casing body which is formed by the side walls and bottom wall and has an opening upper face, and a lid wall closing the opening upper face, the opening vent is composed of a groove formed as a recess on the side wall, the groove having a convexed shape in the side view, a maximum point in the convexed shape being positioned at the lid-wall end side of the side wall of the battery casing, a distance from the lid-wall end of the side wall of the battery casing to the maximum point in the convexed shape of the groove being set between 3 and 20% of the height of the battery casing.