I believe this light is resistor-driven. It has no trouble with LiCo RCR2s, but it does get a little bright (1.1A IIRC) and warm (~3W from the LED, but another 5W from the resistor) on fresh cells. That is outside rated specs, but well within what an XR-E can handle given adequate heatsinking. This is not a light to be left on while laying somewheret.
However, I wouldn't recommend giving this setup to most people I know, because there's a very real risk of deep overdischarge, which can lead to an explosion when you recharge the batteries. In fact, while I'm competent and careful enough that I consider this setup usably safe, I've no intention of using it long-term; I plan to bore the tube for 17500, and add a linear driver for 1x17500/14500 rechargeables or 2xCR2 primaries. If I were not going to mod it, I'd either add protection PCBs to my RCR2s (not sure they'd fit though) or use primaries only. Note that although LiFePO4s will prevent an explosion, they are still liable to be ruined by deep discharging.
