If you are charging your car my understanding is the 12 volt battery will be topped up from the large under floor battery – so if you have been doing a lot of near by journeys and not charging car the 12 volt battery maybe low on charge – your worst case would be the 12 volt battery needs to be replaced – if it were me after an hour or so of charge I would drive the car around the block to see if there are any error messages – if no error messages then I would assume it had sorted itself out and you will get a better nights sleep – if it is the worst case – you need to replace the 12 volt battery at least you know tonight and you can think of other arrangements.
I don’t pretend to be an expert on this but sympathised with your predicament and wanted to offer what help I could – I do hope it is the first case scenario – good luck – hope it all works out ? ?