Fenix LD20/22 VIn range?

Think I read somewhere the VIn range is from 0.9-4.2V, can someone confirm that?
And if that's that case, then is it possible to utilize a single LiIon (14500 or 14670) along with dedicated dummy spacers?

Can someone advise me on this?

Maybe you made ​​a mistake，the right range is 0.9-3.2v.
Alkaline batteries fully charged voltage is 1.6v，So two is 3.2v.
Lithium-ion battery voltage exceeds the LED VF, so LD20/LD22 the circuit does not work properly.
IF you do it,You will get a very bright stalls and can not change it,and may damage the LED.

Perhaps you are thinking of Foursevens Quarks, you can Lego different batt. tubes to it to run Li-ions, or a dummy cell and 1x14500 as you suggest ( but a 1xAA tube pockets better ).

Neutrino said:

Maybe you made ​​a mistake，the right range is 0.9-3.2v.
Alkaline batteries fully charged voltage is 1.6v，So two is 3.2v.
Lithium-ion battery voltage exceeds the LED VF, so LD20/LD22 the circuit does not work properly.
IF you do it,You will get a very bright stalls and can not change it,and may damage the LED.

Click to expand...

A lot of these 2AA lights have a type of boost circuit (step up) because most of the time the battery voltage is below the LED VF as you point out. Only the lights that are designed with buck-boost circuits can accept a wider range of below and above the Vf. The problem from what I've seen is that the buck-boost design isn't as efficient as those without it. Thus I have to admit, I'm more fond of single AA lights and simply jumping over the 2AA lights to either 4AA or 18650 lights.

I've placed Energizer L91's in some 2AA lights and have lost the low mode. New L91's are around 1.80v so that makes it 3.60v total. I wasn't worried about the L91's damaging the led like I would a lithium ion at 4.20v. But what happens is that the total power to the LED is basically the battery voltage minus a schottky diode drop of the switching boost regulator as it simply stops regulating when the input voltage is higher than its designed output voltage.