Follow-Up:
It's not the batteries at fault, but rather how they are abused. In normal everyday use or on long trips they are constantly being overcharged, it's even worse when your land line is plugged in. Keeping the electrolyte level up helps, but disconnecting is the only solution. They make a "battery safety switch" for this purpose. Any brand of deepcycle battery should last at least five years, but because of the above most last less than two. olddon