BATTERY

In an insulating sheet (50), a first left-side piece portion (520), a second left-side piece portion (521), a left-side bottom piece portion (522), a first left-side connection portion (523), and a second left-side connection portion (524) form a first communication path (530) for communicating inside and outside of the insulating sheet (50), the first communication path (530) having a first open end (531) at a position of an end of each of the first left-side connection portion (523) and the second left-side connection portion (524) on the opening (101) side of an exterior package (100). The first communication path (530) is located on a shortest reach path for an electrolyte solution (80) reaching, from the outside of the insulating sheet (50), an end portion (20e) of an electrode assembly (20) closest to a ridgeline portion of the exterior package (100) on the bottom portion (102) side and on the side of one of a pair of second side walls (104a, 104b).