NOVELTY - The method involves providing an on-board electrical system (1) with a low-voltage electrical subsystem (21) having a low-voltage load (29) and a starter (26). The high-voltage electrical subsystem (20) having a high-voltage load (25) and an electrical generator (23) is provided with a battery which is designed to generate the high voltage and to output the high voltage to the high-voltage electrical subsystem. The battery units with line sections are routed to the coupling unit which is designed to selectively connect the battery units to the low-voltage electrical subsystem.    USE - Method for operating on-board electrical system for motor vehicle such as hybrid vehicle and electric vehicle. Can also be used for stationary application such as wind turbine.    ADVANTAGE - The pair of switches is used to individual battery cells to selectively load and unload, and the switchable power supply architecture for an on-board network of the motor vehicle is provided, so that the battery configuration is employed in order to reduce installation space, cost and complexity. Since the boost-recuperation system is increased, the efficiency of the system is improved, the fuel can be saved and the emissions can be reduced. The voltage drop in the low voltage electrical subsystem is reduced. The power dissipation within the forward blocking enabled switch is reduced. The excessive high stresses occur in low voltage electrical subsystem is avoided. The availability of electric power in low voltage electrical subsystem is achieved. The efficiency is improved without sacrificing comfort to the switching of the battery units.    DETAILED DESCRIPTION - The high-voltage electrical subsystem is connected to the low-voltage electrical subsystem by the coupling unit designed to draw energy from the high-voltage electrical subsystem and to supply energy to the low-voltage electrical subsystem.    DESCRIPTION OF DRAWING(S) - The drawings show the circuit diagram of the on-board electrical system.    On-board electrical system (1)    High-voltage electrical subsystem (20)    Low-voltage electrical subsystem (21)    Electrical generator (23)    High-voltage load (25)    Starter (26)    Low-voltage load (29)