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aL1, I'll answer part of this questions. Not sure about using the KK until it dims. I have the same combo, but never let the cell deplete that far. My JM07 steps down when current is too low, so it's safe, but I'm just not sure about the HD2010, so I'd like to know too.
You can charge a single 26650 in the Xtar charger. I use a new world magnet or even two dimes to make contact with the + pole of the battery. Use the 1 amp setting and be prepared for it to take a very long time.
I could be wrong, but I don't think you'll reach 2.75v in a single cell flashlight (without a boost driver, which the HD2010 doesn't have) due to the LED needing at least 3.0v.
-Garry
I believe at around 3.0v (probably much higher, like 3.7) you will see the light starting to get really dim. I can't vouch for this though.
-Garry
26650 are 4.2v.
It's probably best to just run the light with the King Kong yourself and monitor it's output and cell voltage so you can get a feel for what the battery voltage is when the light gets noticeably dim (and to make sure the cell isn't too low when you are starting to see it dim).
If I remember, it's better for the batteries overall life to not discharge it so low.
-Garry
BTW
The 3.7V value is the Nominal voltage, the 4.2V is the fully charged voltage
I use the following for my Lithium cells
4.2V – 100%
4.1V – 87%
4.0V – 75%
3.9V – 55%
3.8V – 30%
3.6V – 0%
My King Kongs just charged to 4.28v on their first charge. At least, that was the “right out of the charger”voltage, it has probably leveled off to 4.2
That was using the 26650 single-cell charger from Intl-outdoor
My cyclone with the Nanjg 105C will blink at 3.0V and go to low light mode, does every 105C do this i wonder?