Charging the battery with generator issue

I would be willing to wager that you encountered a ground-neutral bonding problem. I am actually surprised that you were able to charge at all. An RV neutral is not bonded to ground at the box as it uses the bond from the power source from the pedestal or source where it is plugged. Most portable generators do not have a bond connection of the neutral and ground as a duplicate connection is a no-no. Therefore, when you plug an RV into the portable generator, the converter/charger will often not charge due to the lack of bonding. You can either use an external charger as has been mentioned or make a plug for an outlet on the generator that simply connects the neutral and ground on the plug. Your internal RV concerted/charger will then operate normally.