[OldEngineer]

I can see on your attachment many fault codes for a trailer 'short' of some circuits. All the rest are codes related to the 'Start Up' voltage checks (which will fail for insufficient battery or earth)

So, the Trailer Electrics are poor and you travelled for several miles until the steering demanded extra current and that exposed the poor electrics.

PS. The Battery Monitoring System (BMS) needs to unscramble the effects of separating the two batteries while you charged them. The BMS has no information on the relative battery states.