First and foremost the volt reading you got after the short charge , is a " surface charge ". Or if the genset was still running , all you saw was converter/charger output voltage. To get a true voltage reading the battery must rest for at least an hour , to allow the surface charge to dissipate.
Dead batteries would take 8+ hours to charge from the alternator and two to three times that running the gen set.
Before you go chasing an issue that might not exist .
Remove the batteries from the coach , and have them fully charged and load tested .
More info in this link.
The 12volt Side of Life (Part 1)