If you are plugged into shore power, the on board converter/charger will likely confuse the external charger and vise versus. Disconnecting the battery before using the external charger will resolve this. However, the onboard converter may or may not require a battery in the circuit to provide consistent stable 12v power to the lights and more important the various 12v circuit boards in the fridge, AC, water heater, etc. You need to research your converter to determine if you can disconnect the battery. If you can not, you can throw the breaker for the converter, disconnect the battery and charge the battery, but none of the 12v dependent systems will function while doing so.
