I have to strongly echo this. I was using a small charger/maintainer for years and thought I was properly charging my batteries. I spoke with an Interstate rep and he explained the difference between a car/starting battery charger and a marine/deep cycle specific charger; very different charge profile. I know I bashed Interstate in an earlier post but, with all fairness to them, it may have been my charging habits. But, as humans naturally do, it still left a bad taste in my mouth about them.
Back to chargers; once I picked up a dedicated marine on-board charger, my battery life doubled (on the water time).
So, if you are using a typical car battery charger, you may be doing yourself and your batteries a big injustice.