Battery Power Source

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