An eco-friendly power source such as a battery module is provided for a transportation vehicle, including: a first sub-module and a second sub-module respectively including a cell stack in which a plurality of battery cells are stacked; and a central wall disposed between the first sub-module and the second sub-module, wherein the central wall includes a first central wall facing the first sub-module and a second central wall facing the second sub-module, wherein the first central wall has a rotationary symmetrical shape of the second central wall around a first axis.