Method of manufacturing battery, and battery

A battery comprises: a container 101 including a bottom portion 111, long-sidewall portions 113 each standing on a corresponding one of longer side portions 112 of the bottom portion 111, short-sidewall portions 115 each standing on a corresponding one of two shorter side portions 114 of the bottom portion 111, and a welded portion 116 in which portions of a flat plate are mutually welded; an electrode assembly 102 housed in the container 101; an electrode terminal 103; and a lid 104 closing the container 101, 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.