POWER SUPPLY DEVICE, ELECTRIC VEHICLE USING SAME, AND POWER STORAGE DEVICE

Power supply device () includes a plurality of secondary battery cells () each including an outer covering can having a quadrangular shape, a plurality of separators () interposed between the plurality of secondary battery cells (), a pair of end plates () covering both side end faces of battery stack () in which the plurality of secondary battery cells () are stacked with the plurality of separators () interposed between the plurality of secondary battery cells (), and a plurality of fastening members () each having a plate shape extending in a stacking direction of the plurality of secondary battery cells (), and disposed on opposing side surfaces of battery stack () to fasten the pair of end plates () to each other. Separator () has a spring constant of less than or equal to 500 kN/mm.