Electrical system for a motor vehicle

The power supply has a control device (9) controlling or regulating electrical voltages in an intermediate network (Z), a starter subnetwork (S) and a consumer-generator-subnetwork (V) with an energy storage unit (8). Another energy storage unit (2) is connected to the former storage unit via a controllable switch (12) formed by MOSFETs. The switch is closed only by a control unit (13) designed as a part of the device. Voltages at the storage units maximally differ by a predetermined difference value. One of the voltages at the former storage unit is higher than a predetermined minimum value.