I stumbled across the video below and was intrigued by the idea it’s possible to make emergency welds with little more than jumper cables, car batteries, and a welding rod.
Welding with home-made rigs is not recommended or approved by anyone. But evidently, it works. The YouTube description of the video contains a long disclaimer that begins “A word of caution: When done properly with healthy batteries, this method of emergency welding is safe. However, there are dozens of ways to screw this up and cause property damage and injury. Attempt this at your own risk! I accept no liability for what you decide to do.” It also includes an informal FAQ that is worth checking out.
Why would anyone choose to weld in this manner? For the guy in the video it’s a way to make sure he can get back to civilization if an important part of his vehicle breaks while he’s driving off-road. It's a desperation move, and probably beats walking
For more on welding, including a couple of methods that do not rely on the use of AC power or acetylene and one having to do with welding wood see:
DeWalt Cordless Stick and TIG Welder
Thermite Welding Railroad Track
Five Freaky Welding Videos
Cool Work Wheels: White Motor Company COE
Friction Welding Wood
A final word of caution before you watch the video: I don’t recommend doing this. The guy in the video says to be very careful. And even MacGyver has some concerns.