Harvested Laptop Battery safe to recharge???

Just opened up a 5 year old laptop battery and harvested (6) CGR18650AF’s ( Green Panasonics, I think). Well, I checked the voltage on them and I have (1) that is around 1.8v, (2) at 2.12v, and (2) at 2.56v. The remaining 18650 had less than a volt so I recycled it.

My question is, is it safe to attempt to recharge any of these batteries or have they lost too much of their designed voltage?

What would be the minimum voltage prior to charging that would be safe to attempt to recharge?

Thanks in advance!

It really depends on who you ask. I use anything with a voltage above 2 volts but I also use a hobby charger to measure internal resistance and capacity. If you don't have the ability to do that then it would probably be best to toss them.

I agree with scaru. Get rid of them unless you can properly verify that they are in at least reasonably decent condition.

I toss anything with less than 3V right off the bat.

I Charge them up carefully (monitor them and in a safe area) and after a full (4.20V) charge if the voltage drops more than .10v in 24 hours, they are sent off to recycling. Its just not worth the risk. Plus anything that doesn’t meet the criteria is going to have compromised capacity and isn’t worth hanging on to.

All of the 18650’s I use are from laptop batteries, and the advice of the folks above is spot on!

2.56V yes, but you must be near charger all time!
Other 1.8V and 2.12V no!

I am new to 18650s but I got 6 18650s from my Toshiba laptop. All were under 3v but the pack was not being charged for a few months and was dead when I opened it up. The pack was bad, that is why I decided to salvage it. I charged them all up to 4.13v with a couple only getting to 4.05v. I marked those two and kept an eye on them for the next charge. The next charge brought them to 4.12v like the others and I have been using them since. I have not noticed any problems with any of them including the two that I marked as bad. I plan on recycling the bad ones but so far, they all seem just fine. I even compared them to known good 18650s and could not tell a difference in brightness.

I have four of them in my Sky Ray King and check volts to make sure they are all equal and seem to dischrage at the same rate. So far so good. My advice is to go ahead and try charging them once or twice but monitor them carefully. You have to be careful with unprotected 18650s anyway so I don’t feel like I am taking any risks that using unprotected 18650s already don’t apply to.

I work with electronics and am comfortable around a multi-meter and can tell when something is not right. Once I detect a problem with them, I will not use them anymore but no need to throw the baby out with the bathwater so to speak.

I would use the 4 above 2 volts, but make sure to number them 1a 1b 2a 2b, to keep the capacities about the same.

Thanks all for the input. I guess this is where I’m at …. I recycled the (2) that were under 2 volts and I will monitor VERY CLOSELY the others.

I plan on taking one at a time and sliding them in my charger for 15 minutes, removing them and then reading voltage and checking for excessive heat. I will continue this until I get the “green light” on the charger signifying charge completion. As these are unprotected cells, I will repeat this for the first three charge cycles or so. My charger has only an over voltage protection circuit so self monitoring is key.

If any of them deplete (self discharge) more than .1v in a 24 hour period I will recycle them as well.

Am I taking too much of a chance or does this sound reasonable?

Sounds perfectly reasonable to me.

Thanks to all of you guys! I really appreciate you taking the time to help me out!!!


Harvesting laptop cells from old laptop batteries has become a secondary hobby of mine. In my experience, I cannot judge the

‘health’ of

a cell just from the voltage it has ‘rested’ on when it is harvested. I have a hobby charger and a Pila charger. The Pila and a

hobby charger will outright reject any shorted cell, but on some other cells, I have experienced cells that rested on as low as


but has retained its capacity of up to 99% of its rated capacity. On the other hand, I have had cells that rested on voltages as

high as 2.97V and yet retained only 30% of its capacity. IMO the best way is to recharge each one, then discharge on a hobby

charger to determine its remaining capacity. Most, if not all, of laptop batteries has cells made by Panasonic, Sanyo, LG and

Sony. They are

basically robust cells to start with and are lot safer than buying those counterfeit xxxfire cells.

If you’re lucky enough to get battery packs that came from laptops that ‘died’ prematurely due to electronic failure or user

mishandling, then it’s a good day for you!


For the sake of safety I have recycled 2 batteries that were under 2 volts. I (will) have a cheap charger that monitors voltage only. I don’t want to push my luck with anything that could cause a fire of explosion. I think I’ll stick with the 4 batteries above 2 volts that I got.

Once I get the Pila charger (someday…) I may change, but until then I’ll stick with what I have.

Thanks for the input!

How to measure internal resistance??

Of the 60 or more 18650 cells I’ve taken out of old laptop batteries, all the ones that were between 2 and 3V charged up fine but had <500mAh capacity. Oddly though they kept their charge really well. Of the 32 I recovered from the last lot, 8 were worth keeping and the rest were recycled (mostly due to high self discharge).

At the very minimum charge them outside/ in a well vented area, keep an eye on them and monitor their voltage over a week. Any that stay at >4.1V after a week (ideally 4.15V) should be ok.

A symptom of high internal resistance is during charging, the light warms up. I just got new 18650’s 2 weeks ago, and they don’t heat up one degree during charging, but my 3 year old nicad battery for an airsoft gun gets to probably 100 degrees fahreinheit during charging.

Yeah but how to measure it?

Theres some links on google with good results, but you need some resistors to do it.

Theres even a video too


There’s no need to be paranoid, this isn’t CPF. Catastrophic failures in single cells is almost unheard of. At worse a cell in depleted condition will have poor performance and isn’t very useful, but unless you have a very abusive charger it’s generally safe. Just make sure the exterior isn’t damaged esp during disassembly.

Right now I’m runing test on an old Thinkpad packet rated at 4.8Ah with Sanyo cells still originaly connected together in a 3S2P form. At the time of harvesting cells were 1.98V, 1.8V and 2.4V. I’m using iCharger 106B+. First I have to use NiMh charge mode at low current to bring them up to 3V. Next I’ve charge them all to 3.6 3.7V and rest them overnigh to see if any bigger self discharge taken the place. It didn’t, so I’ve charged them at 2A to full and noticed slightly warm up, but not to hot. I ended up with very equal voltage of each pair (without using balance method), so I can conclude all must be pretty even. Now I’m running discharge at full power of iCharger can use 20W. At 3Ah all three (pairs of) cells are still equal within 0.01V. Will see how it ends up……

EDIT: ended up with 3921mAh and all batteries went up to 3.56V so it looks they still have some juice. Not that bad for at least 5 years old pack. The whole pack has 172mOhm internal resistance.
Yeah, IBM and SANYO :wink: