I scrounge laptop packs all the time. I'm running a moped sized scooter off of used laptop cells. They may not be perfect or as wonderful as EV grade cells, but they also cost me almost nothing. See my battery build page. I quite literally have several hundred used laptop cells running my ride. I check my packs every couple of months and sometimes find a cell or 2 has gone bad, but since they are in battery holders, replacing a dead cell is a quick and easy change out.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=76013
Regarding fires...
All I can say to that is really?! Talk about some serious FUD! My LION packs are made of 100% used laptop cells. I ride them hard and every day. In my motor controller I have it set to cut off at 60 volts or 3 volts per cell. Until just this month, I never even balance charged. Now I have a single BMS that maintains all of them. I pull on average 20-60 amps depending on what I am doing. As far as charging and testing is concerned. When I initially get a laptop pack, I take apart the pack, check each cell voltage and then if they are below 2.5 volts, I charge 4 of them in parallel until they get above 3 volts on a cheap R/C charger. All I care about is that they get above 3 volts each. Then I switch them over to my expensive R/C charger which will do IR and can charge 2 sets of 6 cells at the same time. I've built 2 18650 battery holders into 6S balance battery holders so that I can test 12 cells simultaneously. I then run them through their paces. Each cell is monitored individually. I have yet to see a fire or even an overly warm cell. At worst, I have had a few cells get to 100F, but never a fire. I do all my testing on my desk in my den.
Regarding fires part 2...
I did the math. I have 20S12P of used laptop cells. Assuming they are really 3000 mah cells each, well that's 36Ah and if they are all 2C discharge then that's 72 amps I can safely draw. OK...those are ideal numbers. They assume brand new cells that are all 100% good. I'm running used cells that came out of scrounged laptop packs. I test the cells and don't run them if they are below 2400mah and that happens quite a lot by the way. Used laptop packs quite often have really bad cells in them and maybe one good cell or they may have all good cells. It just depends on the pack. Recently I acquired some 30 laptop packs and 50% of the cells so far are below my cut off of 2400mah and 50% were still worthy of use. My chargers have been running non-stop for days now with not even a single warm cell. So anyway, back to the math. Assuming 2400mah, that means I'm really getting 28,800mah at 1C discharge or 57.6 amps at 2C discharge. I can tell you for a fact that I exceed 57 amps quite often. The batteries hold up pretty well. They get warm to be sure, but no fires...not ever. AND...that's assuming that after 6 months of use that they are still running at 2400mah. I honestly can't say, they consistently get me 3 days of riding between charges and other than an occasional cell that drops out, have worked super well. Even when a cell dies (which has happened 7 or 8 times now), I still don't see a fire.
All that to say, 18650 cells are far more resilient and safe than people give them credit for. Can they catch fire? Yes they can, but so can a steel bar if you have the right conditions. Used laptop cells may not be ideal, but hey they get me going to 50mph every day on a 140 lb scooter plus my 230 pounds!
