I remember discussing battery spot welders, but didn't see relevant results when I searched.
I remember Oil Pan mentioning it and The King of Random made one from a microwave and Linus made one.
I wanted to share a video from a channel that I just discovered. I don't know that he showed anything novel, but I enjoy his videos.
I did find a comment I made a while ago about repairing exhaust manifold cracks:
https://ecomodder.com/forum/showthre...tml#post510393