BATTERY PACK

A battery pack includes: a plurality of battery cells arranged into rows adjacent to each other, adjacent rows of battery cells being alternately shifted to front positions or rear positions in a row direction; busbars arranged to form a parallel group of battery cells by connecting a group of battery cells to each other in parallel, and connecting adjacent parallel groups to each other in series, the busbars including a body portion extending in a zigzag shape in a column direction and a first and second branch portion extending in the row direction from the body portion toward different parallel groups; and expansion pieces protruding from the body portion of the busbar to external positions outside the plurality of battery cells in the row direction or the column direction.