Abstract: A battery includes connector members and a plurality of unit cells connected in parallel through the connector members. Each of the plurality of unit cells having a gradient in a curve of an open circuit voltage with respect to a depth of discharge such that depths of discharge of the plurality of the unit cells are balanced in level to one another.

Abstract: A battery includes a plurality of flat type batteries and a connector member that electrically connect the plurality of flat type batteries to one another. Each of the plurality of flat type batteries is provided with an outer sheath having a composite laminate film, an electric power generating component, which includes a positive electrode plate, a separator and a negative electrode plate and is accommodated in the outer sheath by compelling at least a part of a circumference of the outer sheath to be joined by thermally welded portions, a positive-electrode terminal lead conductive with the positive electrode plate and held between the thermally welded portions, and a negative-electrode terminal lead conductive with the negative electrode plate and held between the thermally welded portions. At least one of the positive-electrode terminal lead and the negative-electrode terminal lead has a surface covering layer made of a metal different from that of its terminal mother material.