A battery module includes a first cell group and a second cell group. The first cell group is provided with a plurality of cells each including a top surface on which terminal are arranged, a bottom face, a pair of long side faces, and short side faces shorter than the long side faces, the pair of long side faces being arranged to be opposed to each other. The second cell group is provided with a plurality of cells each including long side faces arranged to be opposed to each other, the cells being arranged at a position parallel with the first cell group.