Method for managing a system for supplying a vehicle electrical system with electrical energy, the system comprising: - an electrical system including electrical or electronic elements of the vehicle; - an electrical energy storage device ; - an electrical energy generator connected to the electrical energy storage device ; - an additional electrical energy storage device ; and - a unit comprising a switch (K) and a DC/DC converter , the unit being connected to the electrical energy storage device , to the electrical energy generator and to the electrical system when the switch (K) is closed, and connected to the additional electrical energy storage device and to the electrical system when the switch (K) is open; the method comprising the following sequence of steps consisting of: - supplying the electrical system with electrical energy via the additional electrical energy storage device and the DC/DC converter when the switch is open; - regulating the electrical energy generator to supply voltage lower than that imposed by the DC/DC converter and higher than a voltage of the electrical energy storage device when the switch (K) is open and when the discharge level of the additional electrical energy storage device reaches a predetermined value; - closing the switch (K) such that the DC/DC converter imposes a voltage on the electrical system that is higher than that of the electrical energy storage device and of the electrical energy generator ; - applying to the electrical system a voltage of the electrical energy generator that is higher than that of the DC/DC converter so as to supply the electrical system with electrical energy via the electrical energy generator ; and - deactivating the DC/DC converter. - an electrical system including electrical or electronic elements of the vehicle; - an electrical energy storage device ; - an electrical energy generator connected to the electrical energy storage device ; - an additional electrical energy storage device ; and - a unit comprising a switch (K) and a DC/DC converter , the unit being connected to the electrical energy storage device , to the electrical energy generator and to the electrical system when the switch (K) is closed, and connected to the additional electrical energy storage device and to the electrical system when the switch (K) is open; - supplying the electrical system with electrical energy via the additional electrical energy storage device and the DC/DC converter when the switch is open; - regulating the electrical energy generator to supply voltage lower than that imposed by the DC/DC converter and higher than a voltage of the electrical energy storage device when the switch (K) is open and when the discharge level of the additional electrical energy storage device reaches a predetermined value; - closing the switch (K) such that the DC/DC converter imposes a voltage on the electrical system that is higher than that of the electrical energy storage device and of the electrical energy generator ; - applying to the electrical system a voltage of the electrical energy generator that is higher than that of the DC/DC converter so as to supply the electrical system with electrical energy via the electrical energy generator ; and - deactivating the DC/DC converter. <EOS>