My coach is a few years older but I found the onboard charger tended to boil the batteries dry after a week or so.
However, if I stay hooked to shore power in FL for 3 months and constantly use DC power, I have no issues. Not sure I understand that. I do water my batteries with a remote watering system monthly.
Regardless, I leave mine on a battery tender all the time between trips.
Life is a journey, not a destination.
2005 Georgetown 359ts
Bill & Virginia, Kentucky
Nights camped in 2011...78 , 2012...73,
Nights camped in 2013...123, 2014 ...101