(Use science for peace please!) I did really need a spot welder though, and there was no shortage of examples of people who had built their own from supercapacitors, typically in the 500 F range.

Welding cobots expand manual welder productivity by raising arc time per shift, expediting changeovers, and accelerating the ...

The spot welder [Erwin] used is the work of a user by the name of [aulakiria] (link is Korean, machine translation here) and is designed to be portable and powered by batteries commonly used for RC.