The standard factory batteries are "sealed", but they still loose water. I have topped mine up at least 2x in three years. You can carefully pry open the caps, that are connected together in one long strip, then top up the battery with distilled water, leaving a few millimeters of air space.
With topping up the water, regular recharging, and use of a "smart" trickle charger or battery tender during off season, you should be able to get 4 or 5 years out of your battery.