I got myself scrap laptop batteries for very cheap, only 2 cells out of 60~70 appear to be damaged (0v)
To charge 2 drained batteries, first I used a powerbank circuit that despite being less than a dollar does a very good and careful job at reviving low voltage individual pair of batteries, takes about an hour from 1.5ish voltage to 3.7 but it was taking too long so I put 220ohm resistor in series with whole 3s pack to a good 3s 12v battery, idea is to wait for batteries to hit 9v then take it from there, can anything go wrong with this method?
Then to balance the capacities for the pack, I will have to measure capacity of every pair or atleast 1 pair per pack which can also take very long, is there a quick reliable way to test battery capacity without fully charging and discharging batteries?
Regarding charging/protecting the pack, bms will cost me as much as batteries themselves, what if I use bms of working batteries instead, assigning each bms some extra pairs to charge and put all bms in parallel?