NOVELTY - Battery power source has through hole for fixing temperature sensor (4a) formed on chassis wall and groove (330) for wiring formed on outer peripheral surface of chassis wall, which are formed on chassis (3). The temperature sensor comprises a sensor section that is inserted from an outside of the chassis and fixed to the through hole for fixing sensor; 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.    USE - Battery power source for mounting on a vehicle drive system.    ADVANTAGE - The thermal resistance between the sensor and the cell can be reduced, so that the effect of cooling air can be reduced. Thus, highly accurate temperature measurement can be achieved. The position of the chassis in which the through hole is formed is provided, so that the front end, i.e. front end portion of the temperature sensor, which has been inserted in the through hole, is positioned in a region in which the cooling air is shielded by the cell to be measured. This allows the effect of cooling air on temperature measurement to be reduced. Since the protruding portions are provided on the outer peripheral surface of the case and the protruding portions are fitted with the through hole through which the sensor is fixed so as to fix the case, i.e. the casing, to the through hole, the temperature sensor can be fixed to the chassis with ease and workability in assembly can thus be improved. The sensor wiring is prevented from being an obstruction of ventilation.    DETAILED DESCRIPTION - Battery power source comprises chassis (3), in which a cooling air path is formed, where chassis comprises a cooling air inlet (300); cells (2) arranged in the cooling air path; and temperature sensor (4a) that detects temperature at a cell. A through hole 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. The temperature sensor comprises a sensor section that is inserted from an outside of the chassis and fixed to the through hole for fixing sensor, where a front end portion of the sensor section thermally contacts a region of the cell to be measured; 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.    DESCRIPTION OF DRAWING(S) - The drawing is an external perspective view of battery power source.    Cells (2)    Chassis (3)    Temperature sensor (4a)    Cooling air inlet (300)    Groove (330)