This battery comprises an electrode body, an outer package, an opening sealing element, and an auxiliary electrode. The auxiliary electrode has: a first joint part that is welded to an outer circumferential surface of a cylindrical part of the outer package; a plate-like first upward extension part that extends from the first joint part toward the side of an open end of the outer package; and a plate-like external connection part 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 has a groove in which an outer circumferential surface is indented in such a manner as to make an inner circumferential surface protrude.