12V circuit only works on shore power or generator

Would check the relay that does the transfer for the 12V, as with our rv i have 1 circuit that is a direct battery connection for the radio ( separate fuse) , the rest go through the transfer relay, ours also has a battery disconnect switch which will kill all 12Vs from the battery to the 12v panel as well too but still work fine off the generator or shore power but will not charge the RV batter when off.