What's Inside: 1 or 2 x 18650 XM-L Flashlight

I have a no-name flashlight that uses a Cree XM-L.
The body comes apart in sections such that it can be a complete, working flashlight with just 1 18650 cell, or a complete, working flashlight with 2 18650 cells in series.

The brightness between the two is no different.
So, what is the point of using two cells in series? Capacity is not increased by being in series, the voltage supplied just goes from ~4v to ~8v. Can higher voltage translate to longer runtime because current draw is then reduced?

I like the light, so without hacking it apart, how can I tell what kind of circuitry it contains? I have a multimeter if it would help figure out what's happening.
Is the 1 cell getting boosted or is the 2 cell getting bucked or something else? Maybe the answer is the same as whichever is cheaper? :thinking:

If that 8v was going through to the LED it would fry it. Very likely you have a buck driver. If the voltage is too high, the driver "bucks" the voltage back to a level low enough for the emitter to handle it. Result, is light shouldn't be using much more current to get the same output. So runtime should be roughly double.

At least that's my understanding.

Right, sounds kind of stupid when I read it back. Of course the 8v isn't getting to the LED.

I guess the more apt question is how that voltage change affects efficiency. Is it a case of 1 cell = X hours, 2 cell < 2X hours, basically.