Battery power source

A battery power source includes: a chassis 3, in which a cooling air path is formed, with the chassis 3 comprising a cooling air inlet 300; a plurality of cells 2 arranged in the cooling air path; and a temperature sensor 4a that detects temperature at a cell 2. A through hole 302a for fixing sensor formed on a chassis wall and a groove 330 for wiring formed on an outer peripheral surface of the chassis wall are formed on the chassis 3. The temperature sensor 4a includes: a sensor section that is inserted from an outside of the chassis 3 and fixed to the through hole 302a for fixing sensor and a front end portion 401 of the sensor section thermally contacts a region to be measured of the cell 2; and a wire that is drawn from a portion, which is exposed to an outside of the chassis 3, of the sensor section and is set up inside a groove 330 formed on an outer peripheral surface of the chassis wall.