Secondary battery

A secondary battery includes a battery case having a first surface; and a cover that covers at least one portion of the first surface. In the secondary battery, the cover includes at least one extension portion that covers at least one portion of a second surface perpendicularly connected to the first surface of the battery case. The second surface of the battery case is provided with a mounting portion on which the extension portion is mounted, and the mounting portion is recessed inward from a peripheral portion of the mounting portion.