A battery module includes a battery cell, a heat transfer plate, and a holder. The heat transfer plate is arranged side by side with the battery cell and has an edge and is thermally coupled to the battery cell. The holder holds the battery cell and that has a cutout section to which the heat transfer plate is fitted. The edge of the heat-transmitting plate has a first engagement section that is at least one of a first recess and a first protrusion. The holder has a second engagement section that is at least one of a second protrusion, which is fitted to the first recess and a second protrusions, which is fitted to the first protrusion.
