There are many powerful flashlights, some of them have just one 18650 li-ion cell, 10W LED and they are very small.
I have read few tests, I watched few video tests on YouTube and looks like some flashlights really work at 10W power for few minutes and some of them can operate 1 hour at 10W.
For example - there is Armytek Wizard ~1000lm flashlight prototype test here: link
Test results for maximum (about 1000lm) mode:
5 minutes into the runtime test the headlamp is uncomfortable to hold. At the 15 minute mark it is unbearable to hold.
At 56 minutes the headlamp flashed 3 times signaling that the voltage is in the “Warning Level”. This was followed by the ON and OFF switch indicator light flashing once every second in a green yellow orange combination. According to Armytek the “Warning Level” is triggered when the battery voltage is 3.1 V. At this point the light level has not dropped. There is also a “Critical Level”. According to Armytek the “Critical Level” is triggered when the battery voltage is 2.9 V.
At 1 hour and 8 minutes light output drops to firefly mode 2. At this point the runtime test was concluded.
Immediately after the test was finished the battery was removed and checked for voltage and temperature. The voltage was 2.93 V and the temperature was 132°F (for the battery). After about a 60 minute rest the battery voltage was about 3.0 V.
This headlamp has thermal protection built-in which is supposed to be triggered at 80°C or 176°F. When the thermal protection reaches what Armytek calls the “Critical Level” (80°C or 176°F ) the light output drops to 100 lm. During the whole runtime test the thermal protection did not activate.
132°F is about 55°C
I have tried to find that in Panasonic NCR-18650 datasheet, but there is nothing about temperature range exept that discharge characteristics for 60°C exists, so I guess 55°C is ok for discharging. But how high that temperature can be?
What is safe discharge temperature range for (high quality) Li-Ion 18650 battery?