Hi and welcome to the forum!
Yep, sounds like a bad battery but make sure it's not dry, then take it out and get it tested. Check the date on the battery. They should have warranty and purchase information on the label. Is you coach still under some kind of warranty or was it a private party that told you it was new?
Rick, Nancy, Peanut & Lola our Westie Dogs & Bailey the Sheltie.
2007 Itasca Ellipse 40FD