An eco-friendly power source, such as a battery module provided for a transportation vehicle includes a first sub-module and a second sub-module disposed in a first direction, the first sub-module and the second sub-module respectively including a plurality of battery cells stacked in a second direction, which is perpendicular to the first direction, and a lower cover coupled to the first sub-module and the second sub-module. The first sub-module and the second sub-module are disposed to be rotationally symmetrical to each other about a central axis, which is perpendicular to both the first direction and the second direction.