4.2V-8.4V Cree XPG R5 drop-in

[Aquanaut]

I just bought a Solarforce 320lm Cree XPG R5 drop-in that is listed as 4.2V-8.4V. Can I presume full output (whatever it really is) if it is powered by that voltage range? I hooked it up to my bench power supply and the led shuts off at about 2.75V. If I power it with one 18650, does that mean that the drop-in reverts to direct drive below 4.2V, which is most of the time?



Anything else interesting about this drop-in?



Walt