Battery power supply device

A battery power supply device of the present invention includes a battery pack (10) in which a plurality of battery modules (11) each includes a plurality of cells (11a) which are serially connected together both electrically and mechanically, the plurality of battery modules housed in a holder (12), and the battery power supply device is structured so that a cooling medium flows around each cell and/or each battery module; the battery pack is provided with a plurality of vent holes (12c) having different aperture areas which are distributed over at least one of inlet and outlet sides of the battery pack such that a cooling medium having a substantially uniform flow rate flows around each cell and/or each battery module.