The machine: Deere Z-trak 757 with 60" 7-iron deck What happened (in chronological order): - Checking engine oil each week, being my anal self, and noting it had been closer to the minimum line than the middle of the range ever since the fall oil change, so added enough oil (1/2 quart'ish) to bring level up to 60% of range on dipstick. - Went over machine and cleaned out all grass. Noticed rubber boots were not properly in place on positive battery terminal and generator output terminal. Pushed boots firmly into place. Noted battery positive terminal was showing moderate to heavy corrosion, but did nothing about it. - Started machine, all good. - Engaged mower deck and noticed battery / alternator light came on. Never seen that before! - Shut off deck, alternator light goes out. - Ran for several minutes, fiddling back and forth, but continued to see alternator light on any time mower deck was engaged. - Shut down, removed both battery lugs, cleaned with emery paper, greased both lugs with antioxidant electrical grease, and reinstalled. No change in symptoms. - Said, "F-it, it's getting dark," and proceeded to mow lawn. Alternator light went off after several minutes. - Ever since, noticed alt light comes on for several minutes when mower deck is engaged, but often goes back out on its own. - Tonight, about two hours into mowing, the mower deck shut off. - I re-engaged, and the deck ran a few seconds, then shut off again. I have not done any trouble-shooting yet, aside from a quick visual on the wiring. I have not checked the draw on the PTO solenoid, or even located it on the machine, yet. My initial gut feeling was that I probably have a charging problem, but the machine starts with no sign of battery weakness. I have noticed since this started, that my seat switch isn't setting off the way it used to, such as if I forget to engage the parking brake before standing up from the seat. This may be related. It appears this battery is the old-skool type, not the maintenance-free type I've owned in every car I've ever owned, so that's an immediate suspect. I have checked fluid levels and electrolytic specific gravity on a few batteries in my life, but the last time was probably 20-25 years ago.