Oh, believe me, it'll still work fine with a single 26650-you'll get at least 5A out of it and it'll be bloody bright, so don't let me sway you. 
Like I said, I just did the same setup with a 2C host using a 26650 to try it in a smaller size light, and it still lights up the world! If you wanna do it up really nice though, use a 2C host, make a spacer for the battery and you'll have the same setup in a smaller package-and you'll still be pleased!
Rich
Well, you were right. The IMR only pushes it to about 5 amps. Even less with the 3 x Nimh C's. Running 4 C's get me to 8.4 amps. Voltage at idle is around 5v, at full load they sag to 4.5v. The only thing I can think is that with all of the wiring and drivers, there is a good amount of voltage drop. I don't really know the best way to measure the voltage that's making it to the 7135s. They don't seem to get hot, so maybe things will be fine.
Don't even worry about it... with 8.4A you're doing good.Why risk blowing something up fooling around with test leads on those tiny parts?
You got this far-how about some pics?
Rich
Alright, I finally took the time to upload my pics. It's not done yet, but here's how I went about building it so far.
I bought one board with the microcontroller, then 4 4x7135 slave boards. I sandwiched two of those together to make a 8x7135. Takes up more space, but it worked. Here's how the wiring looked before I sandwiched everything together.
Here are the stars mounted in the PES2 heatsink. I drilled a larger hole in the center to allow for the wiring to fit. Following Rich's suggestion, I filed down the contacts that were not used in order for the reflectors to sit flush. See those metal pieces on the side? Those are just random parts from a Maglite that I use to cover the emitter dome when I solder the connections. This way any splattering of solder or heat from the iron doesn't mess up the dome.
Blurry picture, but here it is wired up. I just run one 20 gauge positive wire basically directly from the Maglite switch. Then three separate negative wires each to a 8x7135 board.
It's hard to see, but the reflectors had to be filed down quite a bit to fit with the wiring in place.
And there it is with the reflectors on. I used normal Krazy Glue and was sure that it did not touch the emitter dome. However, it really did dry instantly, so it's a really poor centering job. Oh well, these reflectors don't throw anyways, it's really all spill.
I'll get pictures up later once I get the light completed. I want to do the same thing to the bezel that Rich did, and I'll hopefully get some beamshots up for comparison to some of my other lights.
- Jon
Looks good! Good idea on covering the domes... I've screwed up a few.
Krazy glue isn't the permanent holder it's made out to be. I popped my reflectors off and reglued them when the centering was off. Just scraped off the old glue first with a wrist slicer. (X-Acto #11)
Rich
I finally got the light done and created my own thread...
https://budgetlightforum.com/t/-/5765
Thanks again Rich for the help and inspiration!
Any time! Feels good to have helped. Nice birthday present-I'm fast approaching old-fartdom today. (57)
And this bumps this up so others can see it!
Rich
Happy Bday, Rich !!!!!!!!
Thanks! Like that website BTW... we have 3 dogs.
first post here, but figured this might be useful info. If you want more throw from the XM-Ls (or XP-Gs) the Regina reflector gives a very "flashlight" beam and it fits the XM-L if you drill the hole out to 7mm. I prefer optics for the smoother beam (I make my own mtb lights) and good round ones are the LXP-RS (narrow flood, if that makes sense) and LC1 (not tried yet, but others rate it), all available from digikey. The optics are a bit fiddlier as you have to modify the holders to fit them over the solder tabs. I also like the Laura-RS a lot, but it's a 21.6mm square optic.
Nice first post, and welcome to BLF.
Ah! Cool! Now I know-I didn't know if the Regina would work. Welcome aboard!
Another fellow Pennsylvanian... where are you? I'm in Union County, near Lewisburg. (Bucknell U.)
Rich
Damn you matt! Why couldn't your first post have been a few months ago! 
Welcome to BLF!
I might have to give those a shot. I'm sure I will completely mangle the reflectors trying to drill them out though. And the booms just look so bad ass :)
thanks and sorry! I only popped onto this thread as I have an old incan 4D maglite that I'm idly thinking about modding with a spare LED - nothing compared to this monster though. Even my brightest bike light only has 2 XM-L@3A :)
For drilling out the Regina, it's a piece of cake. Start with a 4.5mm drill bit (or imperial equivalent) and either hold it in your hand or mount it in the drill and turn the chuck with your hand. Once that spins freely, go up one bit size at a time until the XM-L fits inside the hole. Takes me about 5min, more or less. I'm slowly swapping out the reginas I have for optics as I'm not a fan of the pattern for the riding I do, but they do throw really well.
not far from you actually, State College (Penn State). Just getting used to freezing my butt off for another 3 months!
oh, and before I forget, here are some not especially good beam shots :)
I really need to get something better than a polystyrene box to balance things on..
Hmm, good enough beam shots for me! I'll have to order up a few Reginas :)
EDIT: On second thought, it would not be nearly as attractive of a light. I like the hexagon shape of the Booms, and the stepping in the reflector itself. I will certainly keep this in mind for other builds though :)
true, although I don't really give a hoot what my lights look like as it's almost always dark when I'm using them :)
I have one, perhaps 2 drilled out reginas in my parts box, you're welcome to one if you want to try it out
This is my trophy queen light :)
Hmm, yeah, would you like some Booms in return? I have 3 more sitting around that I don't plan on using.
Mag(d)Man stick?