I bought roughly 20 used laptop packs today from someone local who advertised them on CL for $ 40 bucks, i got them all for $ 30 dollars.
Would have been just aswell if i flushed the $30 down the toilet. Every 18650 cell i pulled from them all were all discharged below 2.2 volts. many were at 1.9 to 2.1 volts each, and at least 60 % of them were nearly completely dead at 0.5 volts or less. So now i have a big bag of useless dead cells. I doubt any of them are salvageable, even the 2.0 volt ones? Have anyone safely recovered Lithium Ions that were discharged to that level? I did a quick test in my Chargers, and both the BT3100 & i4 recognized them and began charging them but i pulled them out immediately and left the 2.0 volt cells as they are for now. Are they trash or salvageable?
eas should chime in on this since he's done research specifically tied to laptop battery packs. At 2.2V I would try, but proceed with caution.
Are they all used packs? Any new (unused) old stock?
All used packs.
ouch…very very low…I would say unsalveagable
If you feel you want to try, try a few full recharge cycles, full charge to full discharge to see if they come back alive…monitor them for heat and increased internal resistance…if the heat rises too much, or too high internal resistance…chunk em
used laptop packs are tougher then you think. What have you got to loose (assuming no safty issues).
Start with you high voltage cells and see hw they do. if you get a usable (I think new is unrealistic at this point) then keep goin I bet a suprising number will be “usable”.
I have had good luck with used laptop cells.
I think it would be interesting to get Ir reading on them once cycled once.
I wouldn’t keep them. Though I’ve never researched in depth what damage low voltage causes.
Some people hold the opinion that new old stock that is under 3v can be ok.
Pity. I managed to revive a ‘new’ pack that had self-discharged down to 0.5v or less. Capacity of each cell is way down on what it should be but still better than most Ultrafires and still working several months later.
It’s probably worth a shot, start with the highest voltage ones and bring them up to 3v VERY slowly.
I could let my i4 or BT3100 work their magic and charge them to run some tests, ( the BT3100 has a good capacity test & Charge mode) but my biggest fear is these batteries getting angry and venting during charging.
I used the cells of a battery pack with similar voltages. two of them heated during charge (no more than 60 degrees celsius, but abnormal compared to the others) and their internal resistance proved to ve very high, now that I could measure them with the opus. also the capacity was crap. But the other 4 cells are ok, the capacity is just as original rated capacity, iR is ok, and no heat issues
If you have a safe place to charge them, why not trying? you can save part of those 30$ (or loose an i4 if some cell vents)
I’m sorry to be harsh, but I don’t even understand that concept.
There are so many computer-repair places around here (a cultural if not literal backwater, far from the madding crowds) that you could burn less than that much in gasoline & come home with more batteries. YMMV, of course… And that completely ignores the 5 or 6 new friends you’ll make by offering to relieve them of their burden by taking their old dead packs to the recycler for them!
To a possible solution, when I get any that are stone-cold dead like that, I found that my first charger — one of the unlabeled giveaways (came with 2 free Ultrafire batteries if that says anything), has no problem at all with undervoltage starts and will put 2 of them at a time back to 4.2v in a few hours. I actually don’t know how long it takes, because I leave it outside where if it blows up I won’t know or care about it. I check the voltage fresh, and again after a few minutes. If they’re self-discharging fast enough to notice, oh, well. Buh-bye.
OTOH, some I’ve started at <2.0v are now sitting in my “go-to” boxes, topped off & ready to burn some GaAs. YMMV, of course…
I’ve revived cells as low as 2.4v and about 10 years old. Their capacity was much lower, about 1500mAh instead of 2200 as rated/new. But they came back and had been depleted to the low voltage for a number of years. Usable, but not awesome.
I haven’t had great success with anything below 2.0v.
How old were the used batteries? Personally, I’d see if I can find a battery recycling center or perhaps make a deal with a local computer parts store that has no need of them. Might be able to get newer batteries for cheaper. If a store can’t use them, and is just going to recycle them or junk them, maybe a buck or two each might be appealing to them. I would wager a guess that you’ll have much better luck with batteries that are 4-6 years old at most as well. I was able to recover 100% cells from a few 5 year old HP batteries.
I had 2 down at 2.5 or 2.6 so I only use them in single cell lights as a precaution. No heating during charge and I haven’t checked the resistance
Make magnetic wire leads to connect the cells, and charge them outside and far from the charger in case they vent, if they do, you only loose the wire and not the charger…
better idea yet, ask your neighbor to charge them in his charger! 
I would not give up on them just yet. I have had many in the 2-3V range and most end up decent enough in the 1400-1700mAh range, some even better. Charge them up very slowly the first time - 200mA is good. Make sure it doesn’t get hot. Once off the charger, let them sit for an hour or so and check the voltage. If it’s fallen below 4V, not worth keeping. Check the internal resistance with the Opus. If it’s over about 300 or so, not worth keeping. Do a discharge test at 500mA and see where it sits. After this, you may want to try a discharge test at 1A and see how big of a difference you get.
Not sure I’d mess with the 0.5V ones, but if you wanted to, I’d bring them up to about 3V with very slow charge and let them sit for a week - if it falls below 2V in that time, I’d toss it. If above 2V, follow the process above.
I would not use them in anything demanding a bunch of current, or in multicell configs, but they can still be useful.
I have one cell that was pulled at 1.2V and has about 1600mAh capacity and can deliver 2.5A in a single cell light with no issues.
This has been my experience - have pulled about 150 cells from free packs if that makes any difference.
In the end. do what you feel is safe for you. 
The OPUS BT3100 will automatically charge low voltage cells a a slower rate until it gets up to a higher voltage. For instance, put a 2.0v cell in the carver and set the charge current to 2000mA. It will immediately kick it down to 200mA and as the cell starts to charge, increase the charging rate. Never as high as 2000mA though.
UPDATE: -
- The eight Panasonic CGR18650CG cells that were all at 2.0 volts from the best one of the packs, took a full charge with no problems from 2.0 volts back up to 4.20 volts, and they only got warm during charging on the Opus BT3100.
is it possible these may be ok?
I am letting them rest overnight to see if the voltage drops, then wills run some internal resistance and capacity tests on the Opus charger.
As for the rest of the cells recovered from the other packs, those all tested at 0.15 to 0.3 volts and likely toast.
I wouldn’t pitch any of the >=1.9v cells yet.
I’d give each one 50-100mA for a couple of minutes. If the voltage rises to ~3v in that time, I’d set them aside over night and check them the next morning. If they still are close to 3v, I’d charge them fully at 200mA (each), checking a few times in the first 30 minutes. Any that warm up noticeably, I’d pitch. Any that don’t reach termination in a reasonable amount of time, I’d pitch. Any that drop below 4.15 or so overnight, I’d pitch. Then I’d discharge test them. Any that had enough capacity to be interesting, I’d charge again at a normal rate, again checking for heating.
I’ve been experimenting with new-old-stock and used laptop pulls for the past few months. Even so, I’d say my knowledge is pretty limited and provisional, given all the variables, etc.
With that said, I’ve had great results with new old stock laptop pack pulls that were as low as 2v.
I haven’t done much with any ~2v cells from used packs because the wide range of packs I’ve looked at either have cells closer to 3v, or below 1.5v (some in the negative/reversed-polarity).
I have put a few cells that came out at ~2.8v through 20-80 cycles. I thought they’d decline quickly, since they were already down to 2/3rds of nominial capacity, but they’ve held up quite well.
My reasoning for why I think the the >=1.9v cells are safe for further testing: The ~2.75 low-voltage cut-off limits are for cells under load, where there is a chance of overshoot, so they have a healthy safety margin built in. Battery University suggests that cells that have spent more than 1 week below 1.5v are a risk of partial shorts due to formation of metallic copper structures. I figure that ~2v is above the BatteryU guideline. Further, I figure that laptop packs are protected, and so never dipped below the manufacturer provided discharge limits while under load, if their voltage is low, they came to it gradually, through self-discharge.
As an added safety measure, using low current in the initial pre-charge and charge means that the cell won’t have much energy in it if there is a partial short, and so is unlikely to go into thermal runaway before the short is detected. Checking for self-discharge after the precharge to 3v is a chance to check for partial shorts early.
Thats my thinking, what people do with it is up to them. If people want to pick it apart, thats great, we all might learn something.
I have used several laptop cells that were between 2-2.5. I used an XTAR and had no problems with them. I would keep a close eye on them but other than lowering the capacity they are fine.