A DC-DC electronic power converter for an electric system of a road vehicle; the DC-DC electronic power converter comprises: a high-voltage input, which is designed to be connected to a high-voltage electric circuit provided with a first storage system and with at least one electric machine to generate electrical energy; a low-voltage output, which is designed to be connected to a low-voltage electric circuit provided with a plurality of electrical loads; a conversion device, which is capable of varying the DC electrical voltage and is interposed between the high-voltage input and the low-voltage output; and a control unit, which controls the conversion device; wherein the low-voltage electric circuit is completely free from any storage system arranged on the outside of the DC-DC electronic power converter; the DC-DC electronic power converter wherein a second storage system is provided, which is connected to the low-voltage output and is integrated in the DC-DC electronic power converter; the control unit, when the vehicle is being used, is configured to continuously activate the conversion device so as to have the conversion device continuously deliver the electric power needed to supply the electrical loads of the low-voltage electric circuit and needed to keep the second storage system completely charged; and the control unit, only when the vehicle is not used, namely is parked, is configured to cyclically detect a state of charge of the second storage system and to activate the conversion device only when the state of charge of the second storage system is below a charge threshold and only for an amount of time needed to charge the second storage system. a high-voltage input, which is designed to be connected to a high-voltage electric circuit provided with a first storage system and with at least one electric machine to generate electrical energy; a low-voltage output, which is designed to be connected to a low-voltage electric circuit provided with a plurality of electrical loads; a conversion device, which is capable of varying the DC electrical voltage and is interposed between the high-voltage input and the low-voltage output; and a control unit, which controls the conversion device; wherein the low-voltage electric circuit is completely free from any storage system arranged on the outside of the DC-DC electronic power converter; the DC-DC electronic power converter wherein a second storage system is provided, which is connected to the low-voltage output and is integrated in the DC-DC electronic power converter; the control unit, when the vehicle is being used, is configured to continuously activate the conversion device so as to have the conversion device continuously deliver the electric power needed to supply the electrical loads of the low-voltage electric circuit and needed to keep the second storage system completely charged; and the control unit, only when the vehicle is not used, namely is parked, is configured to cyclically detect a state of charge of the second storage system and to activate the conversion device only when the state of charge of the second storage system is below a charge threshold and only for an amount of time needed to charge the second storage system.