OK...how is this any different than the big battery that we have in an enclosed trailer that powers a 5000# winch. The battery is ONLY charged by the + wire that is on the trailer wire setup on a Dodge pickup. We've used that for several yrs...works fine. Sometimes the pickup is running w/winch ops, sometimes not. Sometimes we don't even have the 7-pin (we have all trailers on farm-type 7 pin) hooked up on trailer 'til later. Is this different? I think the +12 wire on our p/u  has a 10A fuse.

Also-if you hook TC compressor to vehicle battery as per instructions (as we did in '08), the vehicle battery only charges as 13.2 or so volts. I don't think I've ever seen 14.4 V from the tractor alternator (it has voltage readout on dash). So-how is vehicle battery being charged @ 14.4?

Backfeeding? How is that different than if you hooked jumper cables on a tractor hooked to a running vehicle w/a good battery to start a tractor w/low battery?

What am I missing?