You removed the ptc…?
Picture?
Not something I’d advise others to follow.
Chargers won’t reset the ptc, they normally reset on their own when they cool. Sure your not talking about the protection pcb on the bottom? Ptc is built into the bare cell, crimped into the top.
You're quite right of course. My bad... I've never even seen a Positive Temperature Coefficient switch from a Li-Ion cell, let alone removed one. I meant to say PCB. Thanks for catching that.
Here's the culprit. :bigsmile:
Ok, now that I’m home I called a friend with a cheap charger and tried to use it to un-trip my cells…didn’t work. I’ve tried all of the methods suggested here and nothing but three dead cells. I have now removed the shrink wrap, along with the PCB’s, then did a voltage test on the bare cells. One reads in the millivolt range, one is sub 1 volt, and the other is 1.47v. None of the batteries will take a charge from either my i4 or cheap charger. I’m still trying to figure this out, did the PCB do its job or not? These batteries have less than 10 charges on them but they are now junk, due to the light turning on in my bag. I know it was my mistake by not locking out the light, but it seems like a fairly minor mistake to ruin 3 of the four batteries in the light.
Hmmmm, sounds like the batteries did not get the protection to trip correctly. Maybe try connecting the cells in parallel with a good battery to bring the voltage up.
Protection failed. Could you take a picture of the protection pcb and tell us the marking on the small 6 pin chip?
Which FastTech NCR18650B protected batteries were they? You could post in the discussions for that item & raise a support ticket. Protection can sometimes fail, I don’t know how often but 3 out of 4 (75%) seems too high.
I believe there is research somewhere showing that once a li-ion is over discharged it may become internally damaged and dangerous.
Still some people have recharged over-discharged li-ions. I wouldn’t. Unless you live alone and have good insurance. 
edit: typo
Helios, I’m a noob, and don’t know how to post pictures or links. Thought this was too important of a topic NOT to post, otherwise I’m happy being a lurker. The 6 pin chip is labeled DW01. As to charging them, I understand that it is not safe, but it doesn’t matter since they won’t take a charge anyway. I was under the impression (evidentially wrong) that when a protection circuit gets tripped, it acts somewhat like a circuit breaker, and would need to be reset, either automatically or through some manual means.
Thanks for the help.
That is what its suppose to do. It failed to do its job on your 3 batteries.
You could raise a support ticket with fasttech saying the protection on 3 out of 4 of your batteries failed.
Thanks for the DW01 chip markings. 
Well since I cut the shrink-wrap and PCB off thinking (once again incorrectly) that the bare cell would still be usable, I’m pretty sure whatever warranty was in effect, if any, is void. BTW the cell was the Fasttech clear wrapped “protected”NCR18650B. Does Fasttech sell more than one version of this battery?
This just makes me more suspicious of the quality of those FastTech Pana protected cells, well really the protection boards. HKJ stated Panasonic doesn't make the protection circuit, so a Pana cell with protection is an aftermarket assembly (http://lygte-info.dk/review/batteries2012/Panasonic%20NCR18650B%20Protected%203400mAh%20(Green)%20UK.html). I think KumaBear and others were right about the superiority of the KeepPower's.
Also, it seems quite clear the protection circuit in a Pana B cell will vary based on where you buy them, and FastTech, like others, probably has no clue what the true specs and quality are. They do sell protection boards, but I sure wouldn't trust them.
My opinion of FastTech has greatly diminished the more I hear things like this.
That is why I just don’t use protected cells 
There was a chance the bare cell was still be good. People often give that a shot.
Fasttech does seem to have two listings for protected NCR18650B.
Links
$16.98 Panasonic NCR18650B Protected 3400mAH 2-Pack (The listed “4.35V” is wrong)
$16.73 Panasonic NCR18650B Protected 3400mAh 2-Pack
People keep on raving about these batteries and keep forgetting the weak link. Yes, the batteries are Samsung/Sanyo/Pana etc but the circuit is still of unknown origin. Who made them? Who rewrap them? Oh I don’t know, so I won’t test them out and just give them 5 stars hooray.
I have one failed XTAR out of one and one failed Samsung out of four, having problem with the protection circuit. That’s 100% failure rate for XTAR and 25% for Samsung.
On the contrary, I have like 16 or so TF Flame 18650 and 14500 and none of them has any problem whatsoever. 0% failure rate. They stop overcurrent, overvoltage, undervoltage every time. And yes, I do test my stuff.
So before raving about brands and dissing some other brands, just don’t forget the weak link. At least TF has a brand they want to protect, unlike independent “clear” wrappers… who knows how cheap the protection circuit they’re sourcing.
The bare cell will not take a charge. I tried both the i4 and two different “cheap” chargers, that will put out voltage at their terminals no matter what, neither will work. Perhaps I tripped the PTC circuit?
bdiddle- I thought i was doing the right thing by using protected cells in a multi-cell light. Other than the fact that no one got hurt, I don’t see how I got any “protection” from over discharge in this case.
The protection chip looks to be from a Taiwanese company, fortune semiconductor.
Datasheets came up on a Google search .
Wish they used a known quality chip.
Anyone check what chips are in the higher priced branded protected 18650s?.
Scotlarock, you definitely did the right thing using protected cells, the protection circuit should have triggered and shut off the battery, but didn’t.
Definitely you need to talk to FT about this, hopefully they can give you compensation and also test their current battery batch for this fault.
Its not just Fasttech, I’m questioning the Wallbuys cells I got too. I have not had any overdischarge scenarios, but using them in series in a “plunger type” multi-emitter, protection appears to have been tripped with full cells and made me initially think there was a problem with the light. Also, the protection appears very thin/easily dented metal and WP2 charger is making light dents in several cells. I think it may be the cheap protection circuits placed on these batteries from Wallbuys and Fasttech are the same…