Even if you ignore the hours, comparing 2 things at similar price with brutally dissimilar effort to put together is something to think about.
I believe the fun part is the bms and vehicle integration, not the 4000 welds....
Any reason why the VW modules are a bad idea?
Aside from that I haven't stated anything about the VW hybrid modules...
Most importantly I won't be able to procure those VW modules here - at least not at the price you're able to get them. This goes for almost all modules - Tesla modules, IMiev modules, etc. , they're all either expensive or very hard to get compared to the US. And I'm not going to go the Jehugarcia route with recycled batteries or modules; that's even more work. New or bust. That also severely eases the speed at which I need to get my balancer in order; new cells, especially with 4+ in parallel, will be pretty much perfectly balanced for the first 50-100 cycles, so I can iron out any serious issues over like a year of use.
Re voltage of ready-made modules: most are 48V (12S), so that is perfectly compatible with the 96S pack in the Leaf.
Re chemistry: Leaf uses LMO (LiMn2O4), so really only LMO/IMR and LCO/ICR are acceptable chemistries to put in parallel with that. LiFePO4 is totally out of the question, as are non-lithium chemistries. NCR and other nickel/manganese/cobalt concoctions are probably maybe doable, but they have much more linear discharge curves so you'll get significant charge/discharge imbalance over the use of the pack.
As for 4k welds - it's not that bad! I do about two welds every 5 seconds, that's about two and a half hours worth of battery welding. Waaaaay less than all the other work. I figure the actual pack building can be done over a weekend. I've done way worse jobs like pack rebuilds with recycled tabs; now that I would not even start on this scale.
The real effort, work and the real stuff I'm anxious about is the stuff I don't know yet:
- Will I brick the car before I even start?
- Will I be able to actually splice cables on?
- Is there actually enough space somewhere to build on, in a sufficiently convenient shape?
- Can I get the contactor situation to work? I'll probably do this before even buying the batteries
After I have the RLY P/RLY V signals, they work reliably every time and I have a volume of air mapped out to put the pack in, all the work is done as far as I'm concerned. Welding and assembling the packs, doing the BMS, that stuff is all a formality to me. I've done that dozens of times already.