To me, it just doesn’t make sense. You can't spotweld it because the tin/lead coating has no mechanical srength and very low fatigue resistance, so is very likely to break from vibration. Copper is the same. Also, it has to be coated to stop it from corroding, but that's not a problem if you used the tinned stuff.
It's a great idea to be able to resolder all your soldered joints that fail due to vibration, but wouldn't it be better to use the right stuff so that they don't fail? Sure, in the past, we used to hear of the odd bad spotwelds on batteries, but that's extremely rare these days, and whenyou do it yourself,you can check the quality as you go.
Then you add the risk of compromising a cell by overheating when you solder them. How do you know how much you damaged them? Are you going to test the capacity of every cell group after soldering? Is it 99% or 95% of what it should be? How have you affected their life? Are they only going to live half as long? It's all very well saying how great a pack looks after you soldered it up, but how great is it compared with a spot-welded one?
Surely, if you're going to make a few batteries, it makes sense to get the proper stuff and do it properly.
You can buy really good ready-made batteries for less than you can make them, so I find it fairly questionable why anybody would want to make one these days unless you need something special. I still make a few batteries every year, but they're always because I can't buy what I need, like special size or shape, but by the time I've bought everything to do it properly, they never work out cheap.