Don't use 3.6V primary lithiums (Li thionyl chloride) in a powerful light. They are made for very low-current use, such as computer memory backup. Their performance will be terrible in something like an L1D, and they are environmentally somewhat nasty, so using a lot of them isn't nice. But they are great in lights like the Tektite Trek Lithium, an ultra low powered survival light (maybe 0.5 lumen) that can run for several weeks nonstop on one of those cells.
Rechargeable lithiums are 4.2 volts when fully charged, and discharge down to about 3.2 volts (you should not discharge them further than that or you can damage them). Using them in an L1D despite what Fenix tells you is probably not very healthy for the led, for heat reasons. The L1D has a boost converter that brings lower voltages up to the led's Vf, but unlike fancier lights (HDS EDC, McLux PD, etc) it does not bring higher voltages down to the Vf. So the led ends up potentially seriously overdriven.
Anyway the 14500 should not be thought of as an AA cell except by its physical size, since its voltage is completely different and it can damage devices (e.g. digicams) that expect to run on normal AA cells. If you want a rechargeable lithium Cree light that puts out tons of lumens, maybe you want to consider something like a Lumapower M1 which uses an 18670, which is a much more powerful cell than a 14500. Its regulation circuit and its heat sinking is designed for the extra voltage and power, and its bigger reflector will cover a lot more distance.
