Let me start by saying I don't plan on doing this, but the thawing pipe conversation got me thinking.
If you were out on a job site and everyone else has left and you find out your trucks battery is dead, could you use your welding leads to jump start the truck. Obviously you would need to have it in D/C and get the lead right.
What got me thinking of this was it was -12*f and some of the semi's at work would not start. So I took my bobcat 250 out there and ran a battery charger and my torpedo heater off of it. I but plywood around the front of the truck to hold in the heat and let it warm everything up.
But I still had to use my truck to help the batteries by jumping it too. I know it would of started eventually but I had 3 more trucks to start