This is a typical 30AMP RV WIRING Configuration Block diagram.

As you can see here both the CONVERTER/CHARGER and the ON-BOARD BATTERY feed your 12VDC POWER DISTRIBUTION panel.
Just turning off the circuit breaker for the converter/charger will NOT keep the battery from providing power to a left 'ON' 12vdc light. It will keep burning until the battery goes dead.
The sure way is to install a BATTERY DISCONNECT switch at the battery terminals or just simply pull the NEGATIVE BATTERY terminal if is accessible.
Of course running down the battery to a 'DEAD' state is usually not recoverable. You will most likely have to replace the battery now...
Roy Ken