TK10 head on a TK11 body, can I use a 18650 battery?

[Valmet62]

I read that someone on the board runs their TK11 with a TK10 head, so I tried it and I like the set up. My question is can I safely use a 18650 battery with this light ?

Valmet62

 

[Marduke]

Safely yes, but you'll get a low voltage warning fairly soon.

 

[LightWalker]

My AW 17670 3.7V 1600 mah flickers on high, not low, fresh off the charger in my TK10. This battery is slightly smaller with a little less capacity than the 18650 but has the same voltage.