Patent ID: 7638234

Claim:
A battery pack comprising: a plurality of cylindrical battery cells arranged in a plurality of rows and a plurality of layers; a lower case that supports said battery cells and that includes a lower case sidewall that extends vertically from an edge of the lower case; and an upper cover welded to said lower case so as to cover said battery cells supported by said lower case and that includes an upper cover sidewall that extends vertically from an edge of the upper cover; wherein the lower case sidewall includes a first welding surface including a first welding projection formed on an inner periphery of the lower case sidewall, and a first welding recess formed on an outer periphery of the lower case sidewall, the upper cover sidewall includes a second welding surface including a second welding recess that is complementary with said first welding projection, a second welding projection that is complementary with said first welding recess, an upper cover sidewall inner surface that faces an interior of said upper cover, and an upper cover sidewall outer surface that faces an exterior of said upper cover, such that the second welding recess is formed on an inner periphery of the upper cover sidewall, the second welding projection is formed on an outer periphery of the upper cover sidewall, the second welding surface extends from the upper cover sidewall inner surface to the upper cover sidewall outer surface, the second welding projection projects from the second welding surface in a location that directly abuts the upper cover sidewall outer wall, and the second welding recess directly abuts the second welding projection, and the first welding surface and the second welding surface are opposed vertically and abutted on each other and are welded to each other by ultrasonic welding.