i tell most users not to buy flashlights requiring hi-voltage lithium-ion batteries. they require carefully monitored handling and charging. this list might help:

Using high-volt Li-Ion batteries require special care, so here are some rules/warnings:
-Do not overdischarge/overcharge
-Recharge drained batteries ASAP
-Do not short circuit
-Do not dispose of in fire
-Do not expose to extreme heat or water
-Only charge when you can be there watching
-REPEAT: NEVER CHARGE LI-ION CELLS UNATTENDED

the one you listed uses a 18650 3.7v 2400mAh. no thanks. too dangerous for the average user IMHO.

i'd suggest sticking with standard 1.5V batteries (AAA, AA, C & D) in alkaline or Eveready disposable lithium, even if you can't get the same super-bright output.

(remember when 30-60 lumens was considered the top-of-the-line brightest units available to even the military/police, just ten years ago? times sure do change...)