Since my old lead-acid batteries were pretty much shot and I had to crank the weld time up almost to the max, I decided to find something better.
I tried a 6s, 10Ahr LTO battery, running around 15v. This worked reasonably well, but still required a pretty high weld time. A larger Ahr one might work quite well, and these are very safe and last nearly forever.
Then I looked at some Lipo packs. People had reported good results with Turnigy 5.0 Ahr high rate packs. I noticed the 5.0 uses 10ga wires, but there was a smaller 2.2Ahr that also used 10ga wires. I decided to get two 2.2 so I could put them in parallel. These were slightly more than a single 5.0, but I was in the experimenting mood. I got the 3s "Graphene" 65/130C rated ones.
Tiny little buggers. So they shouldn't make too big of a fire if they go off. I cut off the RC plugs they came with and put the wires from both into a single large crimp ring terminal, then used bolts to connect them.
I initially tried a low setting, about 1/4 power. Pow!, got a nice big spark and blew a hole through the nickel. Probe contact was poor on one side (my fault). I dialed it down to about 1/8, which I guess is around 5ms and got nice welds. I was very impressed. These things can belt out some serious amps. I think it might work well with a single one.
I need to work on my electrode setup more, and I also plan to use a wall wart to keep the cells right at some constant voltage (I'm thinking 12.2V).
The whole works could fit into a fairly small case, which would be next.