Most motorhomes have a combined inverter converter. Usually they are made by Magnum Energy or Xantrex. They charge the battery when connected to shore power. Most of them are configurable first battery type (flooded, AGM, gel) as well as any equalization requirements. If the inverter/converter charger fails for some reason it is possible that the voltage is too high causing the batteries to boil. I would check the open circuit voltage when on shore power with everything but the charger off. Then test again with the batteries connected. If you have a higher voltage than 13.8 with the batteries fully charged there’s a problem with the inverter/converter unit. In the unlikely event you have a separate converter the same test applies however you will only need to replace the converter.