Yup, batteries are only leased for a usable time period. The trick is to extend that life so that the replacement interval is longer. More capacity = shallower discharge = longer life.
6V batteries bought through Costco, Sam's club, or golf cart distributor are now so cheap that replacing a marine/hybrid 12V makes economic sense.
For operating a 12 V system off-grid, adding solar charging is like peanut butter to jelly. It just works too well to pass up. An owner also gets the advantage of maintaining battery charge while in storage.