An electrical power supply device for electric propulsion aircraft includes first and second electric motors configured to ensure the propulsion of the aircraft. First and second high-voltage electrical circuits are connected respectively to the two electric motors. A low-voltage electrical circuit is connected to at least one control and/or command facility of the aircraft. First and second pack of batteries are connected respectively to the two high-voltage electrical circuits. First and second battery management systems are connected to the low voltage circuit. Two battery management systems are linked respectively to the two packs of batteries. An electrical converter is connected to the first high-voltage electrical circuit and to the low-voltage electrical circuit.