Hi Matt,
How reliable are these cells and how can I check their viability?
How do you want to measure reliability?
How can you check them? With a lithium-ion capacity checker.
If you pre-charge and post-charge and only use the capacity checker for discharge capacity testing, it takes about 4 hours per cell. Usually devices do 4 cells independently at a time, so 1 cell per hour average.
I have 2 testers, so, 8 cells at a time, 6 times a day (less because I sleep), so, 48 cells a day.
I tested every day for probably 2-3 months. And I have 2-3 months ahead of me if I want to do the next batch.
Also, where can I find 7000+ recycled 18650 cells?
You can't really anymore. There are enough outfits who've bought up all the recycling contracts. Laptops don't use 18650s anymore, so tool packs are your only source.
I worked out a sweetheart deal with a manufacturer to get mine, but the facility has since gone under so I haven't got any more in the last year or so. So, what I got is what I got.