Both my boats now have on-board chargers now, so they require little attention. But years ago I read an article that got my attention and I followed those recommendations for a long time with great results. If you don't already have one, go to your local automotive store and pick up a hydrometer (Prestone has one for just a few dollars). While charging, periodically test each cell until they reach a specific gravity of 1.265. That is the optimum for performance/longevity. Testing will also alert you to a cell that is getting weak. I followed this routine for years on my old Tracker and every battery I put in it outlived expectations.