Batteries - simple question

Have had only standard batteries in our 2007 5er ever since we bought it new and have never had a problem with them. Currently on our third battery in 13 years, about 5 yrs life each. And even at that I replace them before they begin to get weak. We are always hooked up to electric when traveling and when in storage. Never any problem with build up on the terminals at all. Adding water is only slightly difficult to the back cells, but not bad enough to warrant getting maintenance free. I just use a turkey baster to add water to the cells.