Bad 'new' 18650 protected Panasonic?

In March 2016 I bought 4 protected Panasonic 18650 batteries from Hong Kong. I ran all 4 through my xtar vp1 and all charged normally so I assumed they were all okay. I then stored them in their storage box until a few days ago when I got more flashlights to put them in. In the meantime I also got an xtar vp4. When I put them in the charger 3 of them registered and charged normally. I tried the 4th in all 4 slots of the vp4 and both slots of the vp1 and it would not register in any of them. I measured it's voltage on my volt meter and it measured at 3.1v. I tried putting it in the vp4 for 12 hours (.25ma) and it still read 3.1v. I tried for another 12 hours with the same result. So I read some related threads and hooked another fully charged 18650 + to +, - to - for a couple seconds. It still wouldn't register in the charger. Tried it again, same result. Tried another suggestion of doing the same but with a 9v battery. Still wouldn't register - voltage on multimeter says 3.2v. Tried again, no result. Tried hooking the 9v for a full minute - no change, still 3.2v and still won't register in the charger. Any idea why or if there is any way to recover this battery? Also I thought that the vp4 was supposed to be able to recover over discharged batteries where the protection feature had kicked in? Any help would be much appreciated.

Did you drop this battery on the ground? I have had the same problem with a protected brand new NCR18650B in my set of 4. To repair it, I have removed the PCB and no problem with it.

I did drop it but only after connecting the second time to the 9v battery. At the moment I'm feeling like hooking it up to a 12v car battery. If nothing else works I'll try removing the protection (and as a last resort the car battery). I thought though that if the protection was shot it would have read 0v?

I would guess the protection circuit is not tripped but broken. Better do not use a car battery on that cell.

Try discharging it low enough to see if undervoltage protection still works. If so, then try charging it. If not then the protection circuit is probably damaged.

Is it really worth burning yourself messing with this thing? Recycle it.

Gauss163 said:

Try discharging it low enough to see if undervoltage protection still works. If so, then try charging it. If not then the protection circuit is probably damaged.

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I'll give it a try. Thanks.

recDNA said:

Is it really worth burning yourself messing with this thing? Recycle it.

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Agreed. I'm definitely not as careful as recDNA when it comes to my lithium rechargeables, but at the first sign of weirdness with a cell, I bin it.

An attempt to charge a vaguely failing Li-Ion battery reminds me checking fuel level in a tank with a burning match.

vadimax said:

An attempt to charge a vaguely failing Li-Ion battery reminds me checking fuel level in a tank with a burning match.

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It's the protection circuit that's likely at fault (or in a confused state), not the cell. He already tried to charge it, that's how he discovered something was amiss.

Gauss163 said:

It's the protection circuit that's likely at fault (or in a confused state), not the cell. He already tried to charge it, that's how he discovered something was amiss.

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Maybe.. But attempting the remove the protection circuit (which sounds like where this is headed) it is really easy to create a dead short and boom.

Gauss163 said:

Try discharging it low enough to see if undervoltage protection still works. If so, then try charging it. If not then the protection circuit is probably damaged.

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When it discharged down to 2.55v the flashlight still had not shut off but the charger finally recognized the battery and started charging it. However after a little while it again stopped recognizing it. I'll try one more time and discharge it to below 2.5v to see it the protection turns it off, but I'm not hopeful. Thanks much for your suggestion.

ArcticHighlander said:

When it discharged down to 2.55v the flashlight still had not shut off but the charger finally recognized the battery and started charging it. However after a little while it again stopped recognizing it. I'll try one more time and discharge it to below 2.5v to see it the protection turns it off, but I'm not hopeful. Thanks much for your suggestion.

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This seems to imply that precharging is working, but normal charge is not. This is most likely due to a fault in the protection circuit.

Gauss163 said:

This seems to imply that precharging is working, but normal charge is not. This is most likely due to a fault in the protection circuit.

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I discharged it further - down to 2.43v in case it had protection that did not kick in until below 2.5v. However the protection circuit still did not kick in to shut off the flashlight. I put it back on my xtar charger and it charged and stopped over and over doing so for several to many hours - being recognized and charging, then no longer recognized and not charging, several dozen times that I noted and I assume many more that I didn't. At one point the charger showed it charged up to at least 3.1v. Finally it stopped being recognized entirely, for at least 4 hours straight, and I checked the voltage again on a voltmeter and it read 2.6v. Next step I guess is to very carefully remove the protection circuit.

ArcticHighlander said:

I discharged it further - down to 2.43v in case it had protection that did not kick in until below 2.5v. However the protection circuit still did not kick in to shut off the flashlight. I put it back on my xtar charger and it charged and stopped over and over doing so for several to many hours - being recognized and charging, then no longer recognized and not charging, several dozen times that I noted and I assume many more that I didn't. At one point the charger showed it charged up to at least 3.1v. Finally it stopped being recognized entirely, for at least 4 hours straight, and I checked the voltage again on a voltmeter and it read 2.6v. Next step I guess is to very carefully remove the protection circuit.

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I'm just curious why you don't recycle it? Can you ever really trust that battery again?

It takes 30sec to remove the protection. You will have a brand new cell as the one I have. You will see what this circuit looks like.

With and without(right) PCB.

recDNA said:

I'm just curious why you don't recycle it? Can you ever really trust that battery again?

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I think I spent more on coffee this morning than it would cost to replace the cell...

recDNA said:

I'm just curious why you don't recycle it? Can you ever really trust that battery again?

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This Panasonic is top of the line and once the defective protection circuit is removed it should be an excellent battery for several years to come.

gyzmo2002 said:

It takes 30sec to remove the protection. You will have a brand new cell as the one I have. You will see what this circuit looks like.

With and without(right) PCB.

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I can see how it could only take 30s to remove the protection once familiar with it. I was pretty paranoid, read several threads discussing it and took my time and took precautions in case I accidently shorted it somehow. So it took some time, but I enjoyed the challenge, as simple as it turned out to be. I'm charging it up and hopefully it should, as you said, be like a brand new cell.

ArcticHighlander said:

I can see how it could only take 30s to remove the protection once familiar with it. I was pretty paranoid, read several threads discussing it and took my time and took precautions in case I accidently shorted it somehow. So it took some time, but I enjoyed the challenge, as simple as it turned out to be. I'm charging it up and hopefully it should, as you said, be like a brand new cell.

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Did you put on new shrink wrap?