I had the same problem.I put a switch in the line that keeps everything "alive" when the ATV is off. Clock etc. That solved the problem. Hasn't failed to start since I put the switch in. Mine is a 2011 850 Sportsman. I only have 1300 miles on it and is in showroom condition. I've had this problem for years and can find nothing wrong. So either my Polaris has a hidden problem or the batteries today are all junk. I'm on my 4th battery. However this one (since I put the switch in) is holding up just fine and hasn't failed to start or even turn over slowly yet. Problem solved.