This battery (10) comprises an electrode body, an outer package (16), an opening sealing element (17), and an auxiliary electrode (40). The auxiliary electrode (40) has: a first joint part that is welded to an outer circumferential surface of a cylindrical part (30) of the outer package (16); a plate-like first upward extension part that extends from the first joint part toward the side of an open end (31) of the outer package; and a plate-like external connection part (47) that extends from the first upward extension part in a direction different from that of the first upward extension part so as to be connected to another conductor member. The cylindrical part (30) has a groove (33) in which an outer circumferential surface is indented in such a manner as to make an inner circumferential surface protrude. The opening sealing element (17) is disposed on the groove (33) with a gasket therebetween. The first joint part is joined with the groove and/or a portion of the outer circumferential surface of the cylindrical part located between the groove and the electrode body.