I have a 2012 Winnebago Itasca. I bought all new Interstate battery in February, took the coach to Florida for 7 weeks without battery issues. All seven weeks we were plugged into shore power with ...
With a slight load on any battery without any charger on it will go dead in a few hours to days. Once its dead they usually do not charge back up.
Check the battery voltage on each battery using a volt meter. If each is below or near 2 volt DC they will not charge back. The new chargers will not charge a very low battery.
Have you check the liquid level on each cell and each cell voltage. If you do not know how to do that post back.