I hit the recycle bins in my area and get them for FREE. Walk in like I own the place and help myself. This thread has some good info.
The tips I give about newer than three year old cells or packs that show alot of wear on the outside are not concrete. Good cells can be found in any pack but my luck as been better with newer pack and higher capacity cells. If you have 2 packs by all means check them all. But if you luck into 8 or more you can be selective as it takes time to go through 48-72 cells. My best cells to date have been 2600ma+. Have built 4s3p balanced packs (12 18650s) for HID conversions from some of these cells. Check out a couple of YouTube vids on the proper way to disassemble these laptop packs. Use care not short the cells. If in doubt don’t.