When I fully charge two 18650 TF flames and put them in tr-j12 the torch is less bright. As cels discharge brightnes returns. I asked all my family members and they agree. I even took pictures and it is defenetly. I think that bateries are to blame…
What is this for, a second opinion? 
I would put (2) Orbtronic 3100mAh unprotected cells in it and get it out of It’s misery …….
Hmm….interesting. The TR-J12 is actually fully regulated. Unless it is really really lousy and sags like no tomorrow + only 3% charged (say unloaded is say 3.5V), it’d be out of regulation.
That means it always tries to compensate via current draw. ie a good cell like the TF 26650 gets you like 2.0A at the tail only. Other cells like even the Panasonic NCR18650A 3100 can give 2.3A.
All fully charged. As it discharges, the current actually rises to compensate due to the dropping voltage. The brightness maintains. Until a certain voltage level, it drops out of regulation and so brightness drops.
For this light there is no cut-out.