help with battery voltage issue

[burro breath]

so i built a 3000 lumen maglite under the guidence from many great members at candlepowerforums. and i used 4 icr 26650 batteries in series as directed from members. now i have ben using lipos in rc airplanes for over 8 years and am very familiar with them. however my flashlight batteries are lithium mangenese and have the same voltages as li-ion. now the 4 batteries are in my flashlight and i used them dow to about 3.5 volts per cell. i always check the voltage per cell before charging. the cells have 2 cycles each so they are basically brand new. i am not drawing even half the rated amperage out of them. so i go to measure each cell just now before charging and 3 of them are exactly at 3.4 volts...the 4th cell reads 0. is there any hope to bring this back from the dead or is it trash. also what would cause only one cell to drain right down to zero? before i even used any of them i checked all of the internal resistance and they were all the same. so y do i have one bad battery and is there any saving it?

 

[Sigurthr]

You sure that one cell wasn't placed in backwards at some point? Sounds like it was backfed and wiped out the voltage.

 

[BShanahan14rulz]

You said IMR, so probably not protected, but I should ask anyways, does it have a protection circuit?

I think probably what happened is that the PTC disengaged. What kind of currents you pulling from them?