Power source device

A power source device comprising:

• a battery stack configured by stacking a plurality of battery cells each provided with positive and negative electrode terminals;
• and
• a bus bar connected to the electrode terminals of the plurality of battery cells to connect the plurality of battery cells in parallel and in series, the plurality of battery cells being connected in parallel and in series via the bus bar,
• wherein
• the bus bar includes
• a series connection line connecting in series parallel battery groups each including the plurality of battery cells connected in parallel, and
• a branched connection part branched and connected to each of both ends of the series connection line,
• the electrode terminals of the plurality of battery cells configuring each of the parallel battery groups are connected to the branched connection part to allow the battery cells configuring each of the parallel battery groups to be connected in parallel via the branched connection part, and
• the battery cells connected in parallel via the branched connection part in the parallel battery groups are connected in series via the series connection line.