Coach Battery Replacement Help

I'm thinking I've been rather lucky the last 4 years, having non-deep cycle batteries and having never filled them (they appeared to be maintenance free, but I have since read where they look that way, but actually need to be checked and filled). I'm seriously considering getting the AGM's from Sam's--just hoping I don't have any converter issues. I'll probably be waiting another week or so before I make a final decision--waiting on this polar express to retreat back to the North Pole!:)

I greatly appreciate all the responses thus far--it definitely helps. I do not have much experience with the battery/electrical system since this is my first big issue with it. I have learned that if your carbon monoxide detector goes off and you can't understand why the RV reeks of a sewage-type smell, it may just be a battery issue! :B