Battery system

A battery system comprising:

• a plurality of battery cells, and
• a busbar laser-welded to electrode terminals of the battery cells and electrically connecting the battery cells,
• wherein
• each of the battery cells includes the electrode terminal having a surface including a protruding portion that protrudes from the surface, and a welding surface around the protruding portion;
• the busbar includes a welding plate portion that is brought into surface-contact with the welding surface of the electrode terminal, and the welding plate portion is provided with a cut-away portion for guiding the protruding portion to an inner side of the cut-away portion;
• an exposure gap that exposes the welding surface is provided between the inner side of the cut-away portion and the protruding portion;
• and
• the busbar is welded by a fillet weld part that welds an inner edge of the cut-away portion to the welding surface of the electrode terminal and a penetration weld part that welds a boundary between the busbar and the welding surface of the electrode terminal, and the busbar is welded to the electrode terminal in a predetermined welding width by both the fillet weld part and the penetration weld part.