NOVELTY - The device (11) has two electric power storage units (12a, 12b) placed side by side and a connection box (14) mounted on one of the storage units and electrically connecting the storage units. The box has a circuit with connecting units providing electrical connections to two separate distribution networks through accessible terminals (20) and to a specific connection socket (42).    USE - Used for supplying electric power to a starter, alternator or alternator-starter for recharging a battery and/or supplying the consumers of an electrical network of a modern motor vehicle and for starting an internal combustion engine or heat engine of the motor vehicle.    ADVANTAGE - The device is compact and forms a unitary handleable and transportable assembly with two accessible terminals and with reduction of length of electrical connections and simplification of connections. The compactness of the device permits to reduce the connection inductance which produces voltage and resonance ripples between various components and ground offset for signals to be communicated between different equipments of an assembly provided with the device. The reduction of the connection inductance permits to reduce the avalanche phenomena which produce thermal problems. The compactness of the device prevents the multiplication of electronic boxes in the vehicle, thus preventing the multiplication of sealing and cooling imperatives for each box. The compactness of the device prevents cabling and connection behavior problems. The compactness of the device improves the integration and encumbrance of the storage units, converters and switch or interrupters in the vehicle as well as improves the thermal and electrical behavior of the storage units, converters and switch or interrupters during the operation of the device. The device can deliver specific different voltages to several supply networks. Mounting of the connection box on one of the storage units permit the box to act as a cover, thus assuring thermal protection and protecting from dangerous product leakage or avoiding the introduction of certain liquids. The connection box renders the terminals of the storage units to be inaccessible, thus preventing less experienced intervener from accessing voltages other than traditional low voltage i.e. 12V.    DESCRIPTION OF DRAWING(S) - The drawing shows a top view of an electric power supplying device.    Electric power supplying device (11)    Electric power storage units (12a, 12b)    Connection box (14)    Accessible terminals (20)    Connection socket (42)