Will this light accept protected 26650 batteries such as the Keeppower?
Sure, Why not. I’ll take one as well.
Taking some internal measurements, this is what I’m seeing… a cell as short as 64.9mm will just barely make contact, such that a bump or jolt could break contact and shift modes. Maximum length internally is 70.4mm. If a protected cell is longer than 70.4mm it won’t work in this light. For the tail cap to be on all the way and make ground contact, the max internal dimension with springs compressed is that 70.4mm.
But, that is going to fluctuate with different lights, even in the same run, so would it not be better to back off both ends a little, just to be on the safe side? To me, I would think 70.2 mm and 65.1 mm would be a better range. Just thinking out loud here. It doesn’t happen often any more, but I got a little sleep, so I’m rearing to go, 
Also, are the springs heavy enough, in the compressed state, that they will push in the positive caps of cells like the MNKE, which I always found to get pushed in. Every one of those cells had the caps pushed in, just from spring pressure. For an informed member, they would probably think about those things, but for a relative newbie, it might be even safer to say use cells that have a height range of 65.2 mm to 70 mm and leave it at that?
I'm just asking is all. It's something I have found to be particular to 26650 lights. At least I have never had an 18650 dent in. I have had fit issues in many 18650 lights, but not denting of the positive cap.
read post 163 for Start and measure your cells, to see. Don’t have the cells? See what the specs read on several sites and you should be able to find out the OAL. It would be great to make a spreadsheet with the OAL and Diameters of every cell, but I don’t have the cells, nor the ability to do it and they keep pasting new labels on cells every day, so it’s almost impossible to keep up with.
The old F13's I have from O-L's group buy have big springs at the driver and in the tail. The LK/Li cells are pretty short, slightly wider than most. Width wise they fit fine, but in modded F13's with a shorter driver spring, there's some rattle, more significant. In a stock light, less rattle - probably insignificant, no effect. Uncompressed springs without bypass's will lose more voltage, resulting amps.
I just did some head-to-head tests of the EFEST 4200 dark purple IMR cells against LK/Li's, and they are very close, overall slight advantage to the LK/Li. All tests were with the cells at equal voltage charge level, and 30 sec runs on DD FET+1 lights. I used a clamp meter at the tail for amps, and my PVC light box for lumens measurement. The LK/Li consistently had higher amps in 1 cell lights, while the EFEST had higher amps in a XM-L2 triple (11.65A vs 11.73A), but that didn't always translate to advantage in output over the first 30 seconds. In lumens, where the EFEST did better it was by less than 1%, where the LK/Li did better as high as 3.4%. There was a pattern of the EFEST losing voltage faster than the LK/Li from 4.21V (to 4.15V vs. 4.13V),but that should be expected based on the higher capacity of the LK/Li.
I can post size #'s on a bunch of different 26650's, but same as O-L, can't keep up with them all, and some have changed over batch's - BASEN and KeepPower are notorious for that.
Count me in for one unit please.
I have one of the MNKE cells in this one, yes the top plate is dented in a bit, but it’s found it’s place and it’ll stay there now. 
Put me down for one (1) more please. :+1:
Thanks to Dale and OL for the info, looks like it should fit at 69.5mm. http://m.banggood.com/1pc-Keeppower-ICR26650-5200mAh-3_7v-Protected-Rechargeable-Li-ion-Battery-p-1067492.html
I have a Ultrafire F13, it can take my longest Keeppower batteries (71.0mm) without any problems.
I would count it an honor to have this as a memento of even a little of all that you have done. Please add me to the list.
Throw me on the list too please.
Mr. Valleau,
Kindly accept my sincere best wishes and prayers. I hope that you’re getting some rest, able to keep some food down and spend quality time with your loved ones.
It would be my honor to own one of these. Please add my name to the list.
Regards
Update 09-11-16 The F13 samples should ship this week. Once they have been reviewed, the actual production run can start. I am guessing about a month to go, if all goes well, without problems.
Nice, thanks for the update.
If I can give my experience: I faced the problem of the contact of the positive pole can of 26650 batteries by inserting the conical gaskets 3/8 “(for hydraulics) around the positive spring and everything works well, both for the flat pole, or top button (The top button fit inside the gasket)
Interesting idea. I believe all of the F13 will have a plastic gasket, but where in the world would a lay person get such a gasket?
I also think if needed, a gasket found in the plumbing supply section of a hardware might yield a hard rubber or hard plastic gasket that could be easily found for most people. Taking the threaded insert along, one might find such a gasket in repair kits of most hardware plumbing supply shops. In fact, when I get one of the samples, I will pursue that, even if there is a gasket, just to find out what possibilities there might be. EDIT: Well, that is if someone reminds me, as I will surely forget by this evening!
Fingers crossed the production is the same as the sample your hopefully approve of
Yes, I really hope the samples are of high quality. The pics in the OP show a much nicer host than the F13 host I have. The threading is especially much higher quality.
Also, OL, it seems your GB for this host has increased its popularity. I purchased an F13 a few months back as I wanted to make a 26650 triple. To my disappointment, I could hardly find any mention of this host at all on BLF. Now, I’ve seen a several posts outside of this thread mentioning it. Either that, or I just wasn’t looking hard enough.