I got tired of swapping batteries and charge the battery if I use webasto etc.
In my opinion there is something wrong in the is300h 12v aux battery charger.
The chargers thin 230v cable fits between trunk cover & chassis, so I just lock trunk and leave charging on.
https://www.biltema.fi/autoilu---mp/akut-ja-tarvikkeet/akkulaturit/akkulaturi-612-v-15-a-2000045783
https://www.biltema.fi/autoilu---mp/akut-ja-tarvikkeet/akkutarvikkeet/liitantakaapeli-silmukkaliittimilla-2000045817