Have you checked the IR of the used, old cell that was used and is the subject of this op?
10 minutes in, on a LG HE4, on high mode, with tint ramp set to roughly 4000K, the battery cap OUTSIDE surface is already at 40+ degrees Celsius and climbing:
30 minutes in: -now the cap temperature has reached 52.1 degrees C.
for those who say that their T1 still has a “cold” battery cap after running on high for more than 20 minutes i call complete BS.
- I will let mine run with the HE4 cell for a hour or until the temp don’t rise anymore and measure the camp and the inside battery tube.
Wellp, to be fair(er), that’s still not an end-of-the-world scenario.
I took an AT01 that I gave mum, and swapped the 3×AAA carrier with a crap 18650. It needed more pressure on the spring(s) to make better contact (ie, get rid of random flickering), and a Li cell fit the bill nicely. ’Though I’m not going to waste a good cell in case she leaves the light on overnight and burns it down. Ruin the crap cell instead, y’know?
And so she did. Ran it down to vapors by leaving it on, several times. Later complained that after charging, the light would “get hot” when using it (then quickly “get dim” but no longer cook. I figure that pushing the LED with 4.2V after charging, vs 3.whatever when the AAAs would sag under load, was what was heating up. Mmmmmnope, not quite.
When charging it in my not-quite-almighty Opus at a paltry 700mA, the cell started getting quite warm. Okay, back to the AAAs.
Point being, with a lousy cell, pretty much any load would get the cell a-cooking.
see posts above using a 3 month old LG HE4 cell. it still gets very hot.
I initially thought that was exactly the case, that the come-with cell was cooking.
See my last post. Any crap cell will go supernova if it’s already predisposed to do so. Sure, heating it up might be what’s needed to push it over the edge, but that’s not the lantern’s fault. No decent cell would get that far.
Even the Mighty Maglite specifically excludes from its anything-warranty, alkaleaks taking a dump inside the light. You ruin the innards with one-a them, it’s on your dime.
Just saw it now. Unno, I might try it to see.
Half-hour enough to get most of the way to steady-state?
seems like with as many ppl got these lately on here, we might get a better sample to evaluate the problem?
I’m still running it at max. will let ot go to a hour and test again. (right now i have the lantern sitting inside a metal 5 gallon pail just in case it goes thermo nuclear. 
I only have this one T1 to test. (using different cells in it for testing atm.)
I ran my second test on MAX CW using a protected Panny 3400 which I've had in my Fenix for at least 18 months. I got 3hrs 45 mins before cutoff.
I'm without my IR gun at present so a very subjective "pull the cell and hold it" at 30, 60, 90 and 120 mins was the only option available to me. I also reached as far into the tube as I could with my little finger each time. With this test, my light and cell got noticeably warmer than my first test (with the OEM cell on MAX WW) but still not anywhere near what I'd call dangerous. But as I posted earlier, it is winter here (Oops EDIT, actually first day of Spring) with an ambient temp of around 14C (57F) and basic thermodynamic principles dictate that if I run it the same way in another 6 months, it will get much, much hotter.
Just to reiterate, my test was with the lantern hanging by the clip. When I get my IR gun back, I'll try it with the lantern sitting base down on an insulating surface such as a wooden benchtop.
Personally, I think arguments about new vs old cells, petrol vs kerosene and the like serve only to derail the thread. Den pointed out an inherently bad design and a potentially dangerous problem. Surely it is in everyone's best interest to be mindful of the consequences of an overheating Li-Ion cell and operate the lantern accordingly, rather than making excuses for the manufacturer.
Den,
You know how bad luck comes in multiples. We all know you have had your share…….Is it possible it is just more bad luck and you got ‘a bad one’ that slipped through QC?
ok, after a hour running on the LG HE4 18650, as soon as i pulled the cell the battery indicated a 50.6 degrees Celsius after running the lantern on max-mode for that time. The inner surface of the battery tube read a 55.4 degrees Celsius. not “cold” by no means as one mentioned after running their T1 for a time period. Is it safe? probably with good high drain cells like the HE4 , 30Q, 25R, etc. but risky for the general consumer who may poke a cheapo un-branded/unknown cell, or used/damaged cell in this lantern.
I will still stand by my safety concern decision on this as a design flaw, that the battery tube should NOT be the heat sink for the LEDs what so ever, in a lantern, which is usually run for hours at a time, unattended, either hanging in a tent, or on a table, and even when people are sleeping. Sure the good 18650 cells can handle 60+ decrees Celsius, but for constant times? We here know what cells are reall good, and what cells are not. The general public do not know these things.
I would never put a laptop pull,other old or used cell, or any unknown, cheap “ultrafire wrapped” cell in this lantern and use it on a tent or anywhere indoors. Ever with those cells. with a good, quality, branded known cell yes posibly, but not without concerns. I know extended heat duration degrade and shorten the life of lithium Ion cells over time.
to use its safe as we know the limits of good & bad cells, for the un-known consumer, not so much.
anything is possible, and wish i had more than one of these lanterns to test and evaluate for these reasons.
There you go then…all’s well that ends well. Thanks for the experiment. 
Den….
Not sure if you were referring to me about the ‘Cold’ tailcap, but what I said was mine was “cool as the outside of my fridge”…… almost kidding.
I should have explained…. Im in a RV and the AC isnt working in the Deep South so Nothing is Really cool much less cold. Also, I was a pipefitter and I am used to handling hot metal . All that considered, I just ran 1(of 3) of my T1s again for 45 minutes on high CW. I don’t have a way to test exact temp but the tailcap is warm but not too hot to keep your finger on it. If I was guessing, and I am, I would say it is probably less than 40C.
Sorry & my apologies on that, i thought you were serious when you said your T1 was staying “cool as a fridge door” , in comparison to the temps i was getting & testing from my T1 that forced one of my older 3000mah cells to gas the fumes-of-death, all i was trying to put forward here is that this lantern has a flawed design that heats its battery to a temperature that can be hazardous to anyone not educated on LiIon technology who puts an older or damaged cell in this lantern, that has what i consider a flawed design to have the LEDs use the battery center tube structure as their heat-sink.
What happened here was the cell got below 2.5v and started forming crystals inside. At this point the chemistry is ruined and the battery should be discarded.
You can’t just call a battery a “crap” cell. There are many different kinds. There are cheap batteries which are no name brand and low capacity, but work and charge just fine. Then there are cells, high quality and low quality alike, that have been overly discharged and the chemistry ruined making them a “crap” cell.
In your situation, if the flashlight did not have low voltage protection built-in, what you should have done was used a protected battery. That way if the light gets left on, the protection circuitry in the battery will automatically turn off power and prevent the battery from being ruined.
Some protected fit, some don’t. It depends on the length.
You also don’t have to screw the cap in all the way for the lantern to work. I’m not sure if that would cause a water leak around the seal, though.
If the tail cap spring is binding up and preventing the cap from screwing down all the way, you could probably cut the spring length in half so that it could screw down all the way.