A battery pack includes a plurality of cell assemblies arranged side by side, and a restraining member restraining the plurality of cell assemblies along a direction in which the cell assemblies are arranged. Each of the plurality of cell assemblies includes a cell, a first spacer, a second spacer, a first connecting member, and a second connecting member. In adjacent cell assemblies, either one of the first and second extension portions of one of the adjacent cell assemblies and either one of the first and second extension portions of the other one of the adjacent cell assemblies are overlapped on each other between the first spacer and the second spacer that are overlapped on each other.