A secondary battery module includes a row of cells arranged with a gap therebetween, a lid covering one side of the cell row, inner ribs formed on the inner surface of the lid and each determining the gap between the adjacent cells, an outer rim extending along the outer periphery of the lid and cooperating with the corresponding inner ribs to hold the cells located at the opposite ends of the cell row, and a plurality of busbars used to electrically connect the cells in series. The cells and the lid are mechanically connected together by means of the busbars.