NOVELTY - The device has a battery module (3a) with several batteries (20) arranged side by side. A thermally-insulating element (70) is arranged on or above the portion of surface of battery module, to thermally insulate the heat generated from at least one of the batteries.    USE - Power supply device mounted in hybrid vehicle such as hybrid car. Can also be used in electric vehicle and fuel car.    ADVANTAGE - The dissipation of heat generated by battery can be suppressed and battery can be set easily in higher temperature. The unevenness of battery temperatures in the power supply device can be suppressed. The cost of warming a battery can be reduced and the size of the thermally-insulating element can be reduced. The thermally-insulating element can be easily arranged in any types of power supply devices. Since the thermally-insulating element is in contact with the at least one battery, no gap is provided between the at least one battery and the thermally-insulating element. Accordingly, dissipation of the heat can be minimized. The possibility for over cooling of the battery can be suppressed and since the thermally-insulating element is arranged on or above at least one battery located in proximity to the inlet port, the possible to raise the temperature of a battery on the inlet port side can be ensured. Since the thermally-insulating element closes the cooling paths so as not to allow the coolant to flow into the cooling paths, the possibility to prevent that the temperatures of the batteries become too low can be ensured. The thermal insulation effect of battery in proximity to the inlet port can be improved and the number of closed cooling paths or the closed area of a cooling path of the end plate or the separator adjacent to batteries away from the inlet port can be reduced. The additional element is not required to hold the thermally-insulating element. The thermally-insulating element can be more securely and stably attached to the battery module. The lifetime of the battery module can be increased and the power supply device can be flexibly changed in design.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of the battery module.    Battery module (3a)    Battery (20)    Separator (40)    End plates (50)    Thermally-insulating material (70)