A battery used by rolling a pole plate, formed by filling an active material, around a substrate using a band-shaped metal porous body having three-dimensionally linked spaces is inferior in flexibility and likely to short-circuit. According to this invention, grooves are formed in active material-filled substrate filled with the above active material, and then the grooved substrate is pressed flat to form groove active material layers, whereby cracks are made in the bottoms of the grooves preferentially, and cracks are pressed by the groove active material layers and blocked to prevent the flow-out of swelled projections of the cracks and the active material. Accordingly, a higher-capacity and higher-reliability battery is provided.