Battery

A battery, comprising:

• an electrode assembly obtained by winding a first electrode and a second electrode with a separator therebetween;
• an outer package that has a cylindrical part having a cylindrical shape, an open end formed at one end of the cylindrical part, and a bottom closing the other end of the cylindrical part, and that stores the electrode assembly therein, and that is electrically connected to the first electrode;
• a sealing assembly that closes the open end of the outer package together with a gasket, and is electrically connected to the second electrode;
• and
• an auxiliary electrode having a first joint part that is welded to an outer circumferential surface of the cylindrical part, a plate-shaped first upward extension part that extends from the first joint part toward the open end, and a plate-shaped external connection part that extends from the first upward extension part in a direction different from a direction of the first upward extension part, and is connected to another conductive member, wherein
• the cylindrical part has a groove having the outer circumferential surface dented so as to protrude an inner circumferential surface of the cylindrical part, and
• the auxiliary electrode has at least one support part that extends in a circumferential direction of the cylindrical part, and is inserted into the groove.