A battery module includes a plurality of cells accommodating an electrode plate group and an electrolyte, and a single integrated battery case for accommodating the plurality of cells. The ratio of the component resistance including the connecting resistance between the cells to the reactive resistance of the electrode plate group and the electrolyte in each cell, is set in the range of 1:99-40:60 at a temperature of 25null C. Thereby, the internal resistance per cell is reduced, and higher power output and improved service life characteristics are achieved.