A battery comprises: a container including a bottom portion, long-sidewall portions each standing on a corresponding one of longer side portions of the bottom portion, short-sidewall portions each standing on a corresponding one of two shorter side portions of the bottom portion, and a welded portion in which portions of a flat plate are mutually welded; an electrode assembly housed in the container; an electrode terminal; and a lid closing the container, the container having a cuboid shape, the bottom portion being rectangular, the long-sidewall portions each being rectangular, the short-sidewall portions each being rectangular, the flat plate being made of metal and being folded, and the portions of the flat plate being mutually abutting or overlapping.