Did you figure out what was wrong. I have a 720 that is having similar issues. 2 new batteries, from time to time to time even the dash lights will not come on. But hook a 200amp boost up to it and the lights come on and it starts right up. The battery shows it is charging when running. Cleaned terminals and John deere even went through and cleaned all connections. Last night was the first time it has ever died while running? I was pushing snow with the lights on and everything went dead. And not like a kill switch dead, those are slow this was much quicker. Hook a boost/charger and in 20 seconds it's running again.......