Can this light run on; 2x 14500's, or 1x 14500 and a dummy, or 1x 14670 and a dummy/fill-in. And if so what is the likely performance in those combinations.
The input voltage of Fenix L2D is 0.9V-4.0V. You CAN use 1.5 volt lithium batteries with this flashlight, but NOT 3.7 volt rechargeable lithium batteries.
You could probably use a 14500 and a dummy cell. I am currently using a 14500 on my L1D with impressive results. Your best bet for rechargeables would proably be the eneloop rechargeable nimh batteries. They have a low discharge rate unlike other nimh rechargeables which discharge rather rapidly. Not sure about the 14670 and a fill in.