I’m on vacation and brought along my SRK. In a hurry I just threw it in my bag without thinking to lockout. Pulled it out several hours and noticed it was warm. Tried to power it up and nothing. Tripped the protection circuit on 3 of the 4 protected NCR18650B batteries from Fasttech. Inserted batteries in my i4 charger and only one will charge. I’ve searched the forum, but haven’t found a reliable way to reset…
Use a cheap charger to resurrect the cells. The i4 wants a min. voltage from the cells. I've done this a few times. The cheap charger brings it up to a level the i4 will accept, so maybe after a few mins switch over to the i4.
Thanks for the info, funny was going to PM you but didn’t want to bother you. Gifted all of my cheap chargers so will have to wait till home to borrow one.
Applying some voltage for a second will reset the protection.
Perhaps 2 aaa batteries. I would really be hesitant to use a 18650.
Ok, went to the hardware and bought some wire. Jumpered from another fully charged protected 18650, and nothing. I then inserted one of the dead batteries into the battery carrier of my TN31 along with 2 fully charged protected 18650’s just for a couple of seconds and nothing. Are the protection circuits on these batteries able to be untripped? Perhaps once tripped it is permanent?
Thanks kbark, already tried that and no go. Either the protection pcb is now bad or I need take Tom’s advice and find a cheap charger when I get home and try to put some voltage back in that way.
Thanks again
Worked for me. 
Just tried to ’Trick” the i4. Put a ni-mh cell in bank #1 then inserted one of my tripped 18650 in bank #3, I wanted the charger to look for lower voltage in nimh mode. This didn’t work either, so thinking the pcb on the batteries is shot…hmm.
I’d be careful with them now since they aren’t behaving as expected and the protection might have failed.
Thanks for the help Helios, I’m very surprised more people aren’t chiming in on this topic. There is not much info on this either, perhaps I’m not the only one who doesn’t know how these protected batteries function.
When I’ve had new old pulls at low voltage, I switched my cheap TR-006 charger to 3.2V mode and they charge that way. I’ve never tripped protection on any of these…would be good to know if they charge up and are fine or protection did not trip on fasttech’s protection circuits. Please keep us posted.
“these” refers to pulls from laptop / battery packs or NCR18650B with protection? :~
Once removed from the battery pack cells have no protection unless you add it.
When the low voltage protection trips the battery should read 0 volts until its reset. Its 0v because the low voltage protection disconnects the bottom battery contact until it sees voltage coming in (charger).
As Tom E pointed out, a good charger looks at minimum voltage and if too low, decides it’s a bad cell. A cheap charger doesn’t care if it’s safe. It’s the protection built into the charger that prevents charging, not the cell. I believe the cell’s protection, if working correctly, only prevents low discharge and overcharge.
Yes, I havent tripped any NCR18650Bs, of course I’ve never tripped the non-existent laptop pull protection (or maybe I have? Imaginary protection can be set anywhere! ). I recently purchased some protected NCR18650Bs *but from Wallbuys and am wondering if this type of protection/long cells with cheap negative end caps over it even really works. I have tripped a TF26650 flame before, and setting my TR-006 on 3.0/3.2V mode allowed it to reset.
Last time i tripped a cell, i did a parallel charge.
I put one good batt (not tripped) in the charger, put a wire coming from the positive in the charger to the positive of the batt and one coming from the negative to the neg of the batt and started the charge with BOTH connected in parallel (one in the charger one out of the charger) and it charged them both and de-tripped the bad cell. Just don’t leave it on to charge fully, 15 mins should be enough to de-trip the cell, then you can start a charge/discharge cycle for the de-tripped cell. And yes it should work with the i4 charger as you are not doing a direct charge by plugging the batt into the charger on it’s own, your literally bypassing the charge detect function on the charger for the bad cell and using the good cell as a template.
Maybe it’s just my PC but that link takes me to
http://www.lygte-info.dk/info/battery%2520protection%2520UK.html
instead of
http://www.lygte-info.dk/info/battery%20protection%20UK.html
Thanks.
Not just your pc. The link in my post didn’t work.
When checking my post, oddly the link is correct The Anatomy of a Protected Battery. Submit the post and the link dies. I think 25 is the code for ’ ’ and %20 is space. It nullified the %20. 
Only creating a new link using the advanced post editor instead of simple actually seems to produce a working link.
Sometimes it’s the PTC PCB that has failed.
I just got four new protected Small Sun branded 18650s. Out of the box three measured 3.8v and the fourth measured 3.2v. But the 3.2v one would not charge. Okay, the PTC must be tripped… Tried resetting with a VP1 and a couple cheap chargers… No luck. But the cell still measures 3.2v after more than an hour in various chargers. :~
So I removed the PTC PCB and voila… The bare cell’s OC voltage measured 3.8 - the same as the other three cells. Now I need to get some shrink wrap because I want to remove it from the remaining three. J)