Battery -A-, DISCONNECT AND CONNECT, 0K4: Notes
WARNING: This page is about a different car, the 2022 Audi S3, 2022 Audi RS 3, 2022 Audi A3 Quattro, and 2022 Audi A3. However, it is still accessible from the selected car via links, so may be relevant.
The 12 V system is supported by the 48 V system via the Voltage Converter, 48 V/12 V -A7-. So the only way for the 12V vehicle electrical system to be de-energized is to de-energize the 48V system beforehand.