The invention relates to a system (100) with a battery charging device (20) with output terminals and an vehicle electrical system power supply stage (10). The vehicle electrical system power supply stage has a step-up/step-down converter (12), which is designed to raise an input voltage of the vehicle electrical system power supply stage to an intermediate circuit voltage, a direct current intermediate circuit (13), which is coupled to the step-up/step-down converter (12) at intermediate circuit nodes (14a, 14b), and a vehicle electrical system d.c.-d.c. converter (11), which is coupled to the direct voltage intermediate circuit at the intermediate circuit nodes, and which is designed to convert the intermediate circuit voltage into a direct voltage for a vehicle electrical system (1, 2), the output terminals of the battery charging device (20) being coupled to the direct voltage intermediate circuit (13) via the intermediate circuit nodes (14a, 14b).