I bought a printed circuit board set to make an Arduino based battery welder, however, the completed and tested system became available and so I've decided to buy the assembled system. Now I have a PCB set to sell.
See the listing here:
Here's the text...
I purchased this Arduino based battery spot welder PCB set and then opted for the fully built unit. With some fairly inexpensive components and some soldering and assembly skills, you can make this into a battery spot welder for low $$$. I paid $6+1.70 for shipping. It's still in the original packaging and I'll let it go for $7.00 shipped to the continental USA.
Where I bought it from:
KaeptnBalu's github page with all of the parts list and assembly drawings.
Another website featuring this board:
This is what it will look like assembled.