If somone wants to add:
Ultrafire 1AA light (from china) 1W type. is really only for alkalines, a Lithium primary at 1.7V pumps up the ultrafire to a 1.5W output, and increases the heat.
so Alkines for long life, and long runs, lithium for Short HOT intermittant use, that may eventually fry it.
Lithium-ion 3.6v WILL fry it quickly.
Fenix 1AA L1T 3w. will take about anything, on its High position.
alkalines it runs very low , almost to low,
lithiums it runs great, and with its 2 levels is a good matchup, but never really achieved a full 3W , which is good because it would get hot.
with Li-Ion it gets to about 2-2.5W with 4V, as high as about 3.5W with 4.30V which is a bit hot for how small and heat dissapating the light is.
EDIT:make that way to hot . good for intermittant short term use.
2 lights look the same, the light output can be made similar, but thier curcuits are completly different. but both curcuits VARY lots depending on the voltage (battery).
if i compared these cheap curcuits to a GEORGE curcuit, its all the differance in the world, Georges N-flex thing was very very stable at its usable voltages.