A battery module may include a plurality of secondary battery cells; a cell accommodating unit equipped with at least one of the secondary battery cells in a procumbent state; a cover unit coupled to the cell accommodating unit and covering an opening of the cell accommodating unit accommodating the secondary battery cells; and a heat sink unit provided in the cell accommodating unit and the cover unit and in contact with a bottom portion and a top portion of the secondary battery cells to release heat generated by the secondary battery cells externally.