As Bill said, charging while driving is not related to the inverter/charger. While driving, the engine-driven alternator does the charging.
The inverter/charger only charges the batteries with on generator or shore power.
Boiling batteries could be a wrong selection for battery type/technology, a problem in the inverter/charger OR a bad cell in one of the batteries.
So, again, what is the charging voltage and what type batteries do you have (wet cell, gel or AGM)?