I finally got my 3D maglite taken apart. The Alkaline cells in it had leaked badly and I hadn't been able to get it apart until this evening. So, I started rebuilding the LED assembly using a new driver. I have 3x XR-E R2 emitters mounted in a reflector that has been ground down to fit the mag head. Previously, I had this driven by 3 separate drivers, each connected to a separate emitter. I had ordered the DX 3-emitter driver to simplify this build. (http://www.dealextreme.com/p/5v-12v-9w-3-cree-3-mode-circuit-board-for-flashlights-16-7mm-5-6mm-25516)
This light will be running from D-sized 3.6V Li-SOCl2 primaries I am able to salvage in good but used condition from my workplace.
I set 3 cells up in series using magnets and connected the driver/LED assembly to the power source to test before final assembly. I was dismayed that my driver didn't seem to work normally; it would start in high, and immediately go to low mode. I checked current and was only getting ~.3A through the circuit. I thought I had a bad driver. I checked all connections, and couldn't improve. I left it running for a couple of minutes, after which time, I noticed it would eventually drop into the 'strobe' mode. Out of curiosity, I tested with 3x 18650 cells and the driver ran perfectly! Light output was MUCH higher and current was just over 1A meaning the emitters were being driven quite well! I reconfigured my meter leads where I could check voltage under load and connected the driver. IMMEDIATELY the battery voltage began dropping from nearly 11V, quickly declining to about 5V, at which time, the stobe would mode would kick in. As it turns out, the more heavily used cells I had on hand at the moment couldn't handle the current draw. I have fresher ones in my office I'll pick up next week; hopefully, they will be a little more robust than these well-used cells I have on-hand now.
At least I now know that this driver has under-voltage protection... 