edit 23.1.2019: added 18650 results at the end of the post
Many people report that lights can’t sustain their turbo modes in freezing temperatures. I tested four 21700 batteries and one 18650 after they had been outside in (–12°C) for an hour. Their surface temperature was at –1 to –3 degrees Celsius when I started the internal resistance (Ri) measurement. The test was done inside. I did a similar test previously on some 16340s.
For example, estimating that a high power light draws about 10 amps, the voltage would drop from 4.2 volts to about 3.3 volts on a battery with an Ri of 0.09 ohms. This is such a low voltage that the light would most probably assume that the battery doesn’t have enough charge to sustain the turbo output.
A Samsung 30T with an Ri of 0.05 ohms would probably perform better in cold temperatures on high modes. Samsung 30Q acted as an 18650 reference, and it was significantly worse than any of the 21700s. None of the cells were brand new and have several discharge cycled under their belt.
Using a lower high mode a while would warm up the battery, after which the turbo max mode might work.
Testing was done at 5 amps DC at room temperature (22°C) and at about –1°C.
Acebeam 21700 5100mAh IMR21700NP-510A
Warm 0.039 ohm
Cold 0.088 ohm
Liitokala 21700 4000mAh Lii-40A (Manufactured by Lishen)
Warm 0.025 ohm
Cold 0.089 ohm
Wuben 21700 4800mAh ABD4800
Warm 0.043 ohm
Cold 0.097 ohm
Samsung 30T 21700 3000mAh (Vapcell branded)
Warm 0.011 ohm
Cold 0.053 ohm
Samsung 30Q 18650 3000mAh
Warm 0.051 ohm
Cold 0.159 ohm
Data for a couple of 18650 cells. They were outside in –4°C for 3 hours. Surface temperature was 0°C before the discharge test started so not quite as cold as in the 21700 test. The same 30Q performed better this time around.
Very similar results to the previous tests. The lower the internal resistance warm, the lower it is when cold. When at 0 degrees, there’s consistently about 60 milliohms more resistance compared to room temp of 23°C. Sanyo GA increased 80 milliohms.
Warm 0.052 ohm
Cold 0.112 ohm
Warm 0.033 ohm
Cold 0.090 ohm
Warm 0.069 ohm
Cold 0.149 ohm
Warm 0.027 ohm
Cold 0.083 ohm
Warm 0.037 ohm
Cold 0.102 ohm