Battery having a terminal lead surface covering layer and related method

A method of manufacturing a battery, comprising:

• preparing a plurality of flat type batteries each of which is provided with:
• an outer sheath having a composite laminate film made of polymer and metal;
• an electric power generating component including a positive electrode plate, a separator and a negative electrode plate and accommodated and hermetically sealed in the outer sheath by compelling at least a part of a circumference of the outer sheath to be joined by thermal welding to form thermally welded portions;
• a positive-electrode terminal lead conductive with the positive electrode plate and held between the thermally welded portions to be exposed to an outside of the outer sheath;
• and
• a negative-electrode terminal lead conductive with the negative electrode plate and held between the thermally welded portions to be exposed to the outside of the outer sheath, at least one of the positive-electrode terminal lead and the negative-electrode terminal lead having a surface covering layer made of a metal different from that of a terminal mother material of the at least one of the positive-electrode terminal lead and the negative-electrode terminal lead;
• and
• electrically connecting the plurality of flat type batteries to one another,
• wherein the surface covering layer is formed on areas of the positive-electrode terminal lead or the negative-electrode terminal lead in which the thermally welded portions are held in contact.