I don’t know if it’s watertight with either battery. But I do know that the 14500 is the wy to go if you want max output.
I just slipped a new unprotected Trustfire Flames 14500 into my T10. Perfect fit and man this thing is unbelievably bright on med and high !! >)
My protected Flame did fit, but damn it gets hot fast :D
Back to 3rd gen Eneloops 
The medium on flames looks a little brighter than when on high on E91….Use high for short bursts…when it gets warm to touch shut er down or drop to medium. 0:) >)
I have a Trustfire protected 14500 in mine. Fits perfectly.
And you guys can thank Rick on this one. I know I couldn’t believe the difference.
Rick’s the man!
yeh, my protected flames had issues with wrappers and i had to wrap them in electical tape. Too tight for the T10 tube but fit in other tubes just fine.
Thank you… 
My T10 did not have any thermal grease under the star, I applied arctic silver under the star and a tiny bit on the threads of the pill and proceded to tighten the pill hard to increase thermal transfer, now it gets hot right away, I think everyone who is going to use Li-Ions should check under the star to make sure that at least thermal grease has been applied.
I’m not sure, but is this the white thermal paste referred to under the star?
None on the threads btw…came out so easy.
dam,can’t get pic to show
Yes, that one in the pic has plenty of thermal grease (white substance under star) mine did not have any, so I used Artic Silver
Mine gets hot enough off 1.7v Energizer Ultimate Lithium batteries.
It does a good job for the size, but if I need something brighter Ill grab something else instead of risking killing a $30 light for a few mins of 300 or less lumen.
Take a guess:
Did my Thrunite T10 flicker on 1, 2 or on 3 modes when I used 14500?
Shipped it back a while ago.
Only medium flickered but mode change got pretty random.
Mine works great.
+1 And I don’t intend to burn it out on high…just for short burst.
If mine does burn out which I doubt that it will, I’ll just replace it with a new one.
I tried a 14500, and didn’t think the difference was big enough to make me switch from eneloops. The Ti is different though. With a 10440 the low is equal to the high on NiMh, and the high is really bright.
I'm sure you've already seen HBomb's excellent review. I added the lumen output of the T10 on both eneloops and 14500s. Btw, my particular T10 flickers horribly on medium mode. You can find the post here:
Thanks Match. I filed your specs in my Evernote flashlight file.
I put a 14500 in mine a day or two after receiving it. it gets SILLY hot so at least I know the heat transfer is working as designed.