Odyssey Battery! I have a 5 year old Odyssey battery in my wheeler that is in storage for 5 months during the winter. No trickle charger, just pull it out in the spring and start it up. Plenty of cranking power even after sitting all winter. My Odyssey battery should last 10 to 12 years and costs about the same as a regular ATV battery. Ebay and Amazon have them.
