Per the care instructions for my AC Delco Deep Cycle batteries.
Do not leave the battery connected to any type of battery charger after it is fully charged
Using trickle chargers over long periods of time will shorten the life of a battery. The Voyager maintenance free design has a very low discharge rate in storage, eliminating the need for constant low level charging. If the battery is stored for six months, recharge it in accordance with the methods shown in this brochure to keep it ready for immediate use.