Now it definately sounds like a charging issue. If the system isn't putting out enough voltage to charge while running and operating the PTO, then eventually your batter gets too low on voltage, and the PTO can kick out, and you will need another jump to get it started again.
My tractor was doing the same thing, it would run for a while, then the ignition would start to break down.. I put a new battery in,, thought that was the problem, and soon that battery was dead, and frozen. So, when the 2nd new battery started losing it's voltage, I knew it was time to come into the shop and put a tester on it. Sure enough, no charging voltage, and the tractor was just running on battery power. I ended up finding the plug at the voltage regulater was off the block, and once I plugged that back in, everything came back into spec.. charging,, even with the wiper, and extra cab lights on.
So, i'd save the money for a new battery until you verify that the charging system is working properly... I believe there is a stator on that motor, and a voltage regulater someplace... and a few wires that could even be broke or unplugged!
good luck.. keep us posted.
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