A battery includes a first power generation element, a first outer cover body which encloses the first power generation element, and a first planar electrode having, as principal surfaces, a first connecting surface and a first protruding surface opposite the first connecting surface. The first connecting surface is electrically connected to the first power generation element. The first outer cover body includes a first covering portion provided with a first opening. The first protruding surface protrudes from the first opening toward an outside of the first covering portion. The first covering portion is joined to at least one of the first planar electrode and the first power generation element.