BATTERY

In an insulating sheet, a first left-side piece portion, a second left-side piece portion, a left-side bottom piece portion, a first left-side connection portion, and a second left-side connection portion form a first communication path for communicating inside and outside of the insulating sheet, the first communication path having a first open end at a position of an end of each of the first left-side connection portion and the second left-side connection portion on the opening side of an exterior package. The first communication path is located on a shortest reach path for an electrolyte solution reaching, from the outside of the insulating sheet, an end portion of an electrode assembly closest to a ridgeline portion of the exterior package on the bottom portion side and on the side of one of a pair of second side walls.