WeAreTheWatt is building a DIY LIPO Battery Spot Welding project. The construction is very nice. The PCB is very well laid out but of course even with a very heavy copper clad board it would not be able to handle the amount of current he needs. Heavy bus bars are used to pass the current through the fuse and across the switching transistors. There is a foot pedal activation method or a neat self detection method which watches for the leads being pressed against the thing to be welded and then passes the desired amount of energy.