You mean this?
I don't trust myself to not screw up at some point with it, let alone other people who may pick up the light. I think that a dedicated battery carrier may be in order. Bore out the M6 tube and slide it in.
Just to be clear: I'm not mocking Mike C's build, in fact I think it's quite cool, but it's just not for me.
The nice thing about the M6 is that it can be thrown like a hand grenade if it starts smoking. 
Boring it out for a cell carrier sounds like an interesting idea, and certainly far safer to keep the dead-short gremlins at bay.
If you plan on making a dedicated battery carrier for it, why bore out the tube? Why not make a 4 leaf clover shape to match the contours of the housing, with 1 or more smooth connecting rods running down the center of the batteries. Once inserted the batteries would lock the carrier in place to prevent twisting of the top plate. There appears to be enough room to insert 2 possibly 3 smaller connecting rods in the center of the batteries if twisting is of concern, however if engineered properly the top plate would lock into the grooves cut into the housing for the batteries and twisting of the battery carrier would be an impossibility.
I agree Hi-Beam, that is pretty much what I was thinking about too. With the clover leaf plate to convert to 2S2P the button top cells of 2 would be in contact with the driver as usual, the other 2 would be in contact with the springs. That should work fine and removing the battery tube for changes wouldn’t impact anything, it would be necessary to remove the tail cap to get to the other 2 cells though, right? Unless the carrier would slide out, which should also work. Maybe a hexagonal shaped aluminum rod in the center of sufficient size to allow the use of 2 or even 3 small screws to prevent twisting when out of the tube?
LCK-LED just emailed me also about the 50s and said they will be in stock on the 26th of this month.
Aren’t they in Germany?
Mouser will have 50’s in stock the 23rd of next month, they say.
Are these the warm ones at 3000K?
There’s only 0.30” between the cells in the M6. Maybe a square shaft?
Ok, looking at the light, why not simplify? A block of pcb material crossing the driver end could have contacts to touch the negative end of the blocked cell and also the retaining ring. The pcb with springs in the tail cap could then be modified to tie the 2 groups of cells together for series. Batt + would be the two button tops, as usual, Batt - would contact at the retaining ring. That one simple block would do it all. The 2 cells that are inverted will sit deeper in towards the tail cap as the springs won’t be on that end, but on the block end instead. Smaller springs perhaps, to facilitate loading the cells to start the threads. The cells themselves are held in place within the tube by it’s machining.
I have a 12” x 12” x 1/2” thick pcb plate of flame resistant material made for electronics. I think I’ll give it a go with that or with some 3/4” thick G10 I have.
The carrier would be removed to insert all four batteries, no need to remove the tailcap. The batteries would never come into contact with the driver or tailcap, contacts would be built into the top and bottom plates of the carrier. The existing bottom spring contact plate would be removed to create more clearance.
A solid square shaft would be best as long as it is oriented correctly during assembly.
That is very tempting…. but I think i’ll wait a few weeks to see if the cost comes down at all.
DBCStm, I think that the TK75 extender kit is a go. Just need to get a new cap or get the tube rethreaded.
I thought it might work but didn’t know about the threads. Figured if nothing else, the carrier is good. 
That’s why I suggested a contact plate. I’m making a new driver for another light and will not use springs in it like I did with the M6, I’m making a contact plate that can take twisting as it’s the only feasible way of opening this particular light. As long as you fix the pole specific contact plate on the battery side of the tube you can twist it however you like, as the contact plate on the head side will have round “leads”. Of coarse, fixing it to the battery side is the crux, but for me it’s worth solving that rather than running 8 x 18350s.
However, a dedicated battery carrier would be even better, but I’d hate to have to boar out the M6 body. I think I’d go with a different host to start with… but of coarse, if you can boar out the M6 and provide battery carrier for it, you’ll have at least one customer for the host and carrier 
So I’ve been going through many design iterations for this M6 battery carrier / floater plate thing-a-ma-jig for the last half of the day… The cheapest, least invasive, safe, and quick design I’ve come to is this…
First, with the factory board at the tail, cut all the traces like Mike C did in this pic.
Second, remove two of the springs from opposite (diagonal) corners and replace them with a solder blob or 6x2mm brass buttons that you find at FT or MTN. Connect each of these with a mate that is still sprung with a silicone insulated wire.
Then for the hard part…
Someone (I’m trying to learn how to do it myself finally) needs to draw out an oshpark board for the front end. I have it drawn in Google SketchUp, but there’s still work to be done obviously.
The front board will look like a ‘pizza saver’ once complete, and will sandwich between the body tube and the brass driver retaining ring for the negative current path. Springs will be used on the driver side of the plate for (+) positive contact to the driver. The key design element of this setup is the four 5/16” nylon legs that will locate/center the contacts and make it impossible to rotate and short cells as it’s tightened. I spec’d out 5/16” OD by 7/16” length #4 nylon standoffs (tubes) and some oversized (#6-19) plastite type screws to secure them to the board.
is it possible to get 4022 lm from this led?
Please refer to post #274 from djozz - Cree XHP70 up to 4022 Lumens and XHP50 up to 2546 lumens - Multi-die leds.
ok that seem possible, will try to do it with many 22650 battery, will like to use 9.
what driver do you use for for the eagle eye x6?
I managed to order one of the XHP70 emitters from DigiKey.
Now I’m trying to figure out where to get a sink pad. Ideally, since I’m in Canada, I’m looking for a “shipped free” pad - which generally takes me to eBay first.
I’m scratching my head trying to figure out what has the same pad footprint as the XHP70. It seems like XML is too small and MTG2 is too big.
Am I missing something obvious?
