2 years later and I still have basically the same issue. I am replacing the key switch as I messed mine up yesterday. Since the last post I have taken the starter apart and cleaned it but no obvious issues observed. I put it on to charge to get a full charge, plugged in the block heater. 3 hours later it cranked right up. I wasn't ready to use it at the time, I had to go get my pallet forks from another farm. Did that today and after about two hours on the battery charger to top it off during which time the block heater was unplugged, however it had been charging all night, the engine cranked for a short burst then starter stalled again. No whine this time. I am betting this tractor hasn't ran 10 times since the last post all in warm weather.
If it were warm this thing would fire right up. I picked up a block heater for it, but it's never convienient to install when it's 20 deg.