I had heard that using a Li-Ion 10440 cell in a Preon 1 could get close to 200 lumens of output, but I was skeptical. I had to try it for myself. While I have no way to accurately measure lumens, I can say that the claim is absolutely believable and I offer you some beamshots as exhibits. (All photos were taken with a Canon T3i set at 1/320, f/4.0, ISO 400)
Each of the following animated gifs shows 2 side-by-side beams from 2 different 4Sevens Preons on low/med/high and the caption below indicates which beam is which:
1-AAA NiMH/2-AAA NiMH
This is to be expected. The 4Sevens website states that the Preon 2 more than doubles the lumen counts of the Preon 1(70 lumens to 160).
1-AAA NiMH/1-10440 Li-Ion
Again, this is to be expected. We are comparing a 3.7v battery to a 1.5v battery.
1-10440 Li-Ion/2-AAA NiMH
This is where I got excited. Not really surprised, but excited that a single cell could so obviously outperform the 2 AAA batteries.
My completely unscientific comparisons found the Preon 1 with the single 10440 Li-Ion battery to be brighter than even the Preon 2 with two AAA NiMH batteries. How much brighter should be measured with a scientific instrument, but I would definitely believe that the Li-Ion Preon 1 is 40+ lumens(25%) brighter than the NiMH Preon 2. It is pretty cool to have access to so many lumens in such a small package.
The 10440 batteries can be purchased from Super T Manufacturing.
This is not an endorsement for Li-Ion in the Preon and this is not recommended for an EDC setup. The Preon head heats up very quickly and could cause damage to the circuits. Your light will no longer be under warranty.