I had the same problem with my 1999 Holiday Rambler Endeavor. My RV has two coach batteries and two engine batteries. It originally turned out to be a faulty inverter. I had that changed out. Shortly there after, I started having the same problem again. Since the coach was used only 1-2 times year, I could not determine what the problem was. I replaced batteries every year. I was fortunate to stumble onto the name of a long time RV electrician who knew immediately what the problem was. I had the batteries replaced so many times by many different service centers. Each time the batteries were hooked up slightly differently. After a while, the batteries would not charge at all. Once the batteries were installed correctly, I haven't had any more problems. I took pictures of all the hookups and keep it inside the battery compartment so there is no confusion. When I take the coach in for service I tell them to use the pictures as a guide. Before I take delivery of the rv, I double check to make sure the batteries have been installed correctly. I have not had a single issue with the batteries in the last few years.
