The present invention relates to an electrical power supply device (25) for electric propulsion aircraft comprising a first and a second electric motor (20, 21) which are able to ensure the propulsion of the aircraft, a first and a second high-voltage electrical circuit (26, 27) connected respectively to the two electric motors (20, 21), a low-voltage electrical circuit (28) connected to at least one control and/or command facility (49) of the aircraft, a first and a second pack of batteries (31, 32) connected respectively to the two high-voltage electrical circuits (26, 27), a first and a second batteries management system (34, 35) connected to the low-voltage circuit (28), the batteries management systems being linked respectively to the two packs of batteries (31, 32), an electrical converter (37) connected on the one hand to the first high-voltage electrical circuit (26) and on the other hand to the low-voltage electrical circuit (28).