The DC cabinet battery keeps discharging
If the car has no troubles (issues, faults), you should be easily be able to keep your 12V battery in good condition. Just when you open the car go directly to READY mode or UTILITY mode so that the 12V battery is charged through the DC/DC converter or 800V/14V, that is all. (= ICE engine that you start to let the alternator charge your 12V ...