If the converter fails, you are on battery until it dies. Idea is to have spare charger that will recharge the battery. Amps size of that should be within generator's VA and high enough to keep gen time low.
If on shore power, still on 120v but on battery for 12v, same thing but now question is can the charger act like a power supply same as the converter does, or does it shut down when the battery is charged up? Most of them are like that so you still need the battery for between recharges.
If the scenario is shore power but no battery and converter dead, you need a charger that will stay on like a converter does. It will need to be about 40 amps to run the RV 12v stuff.
