A battery includes: a casing that includes a plurality of exterior faces having outer faces facing mutually-different directions and has an arrangement concave part formed; a cell that is housed inside the casing; and a connector that includes a connection terminal connected to an electrode terminal of a connection apparatus and is arranged in the arrangement concave part, in which a face forming the arrangement concave part of the casing is formed as a concave part forming face, and the concave part forming face is present between the exterior faces and the connector.