BATTERY

Provided is a battery including a case and a cap plate. The case is a cylindrical groove structure, a top end face, facing towards the case, of the cap plate is provided with an annular protrusion, the annular protrusion has a central axis coinciding with the central axis of the cap plate, an edge of the top end face of the cap plate is provided with a first welding platform face, the first welding platform face is arranged circumferentially around the annular protrusion, and an outer sidewall of the annular protrusion and the first welding platform face constitute a stepped face. The annular protrusion enters the interior of the case via an annular bottom end face of the case, and the annular bottom end face of the case is in contact with the first welding platform face and connected to the first welding platform face by laser welding.