Energy board net with improved charging strategy for the supplementary battery and respective method

Second power store (SPS) (2) links to a vehicle's power supply (VPS) via a controllable charging and separating unit (16) with switching devices (SD) (S3) to link the SPS to the VPS. Electric power control (12) generates control signals for the SD with semiconductor switches (T1,T2), i.e. field effect transistors, and connects the SD to recharge the SPS. An independent claim is also included for a method for recharging a support battery in a motor vehicle's power supply with a main battery and a support battery.