[quote=DB Custom]
I also recently found button top LG HE-4’s for less than $4 apiece. This is a very viable alternative, having a bit less capacity but still a very capable cell.
Please, where did you find them for that price?
Please note poor performing cells will not maintain regulation running at 2.5A, they not not even achieve regulation, while very good performing cells like the 30Q's will maintain regulation for a significant part of their charge life.
The XHP35 HI at 2.5A draws over 13V, so if you can't get over 13V out of the cells taking into account resistance loss's, than the LED falls out of regulation, and output drops as the cells deplete. It's only a buck driver, not boost.
Therefore I do hope for low resistance springs in the carriers (is that the plan?), which is the single most effective measure against voltage loss. 2.5A is not much so voltage losses can be kept low with such simple measures.
Please add me to list for two!
Hmm…
So , Tom , a cell like GA or 35E will have a big advantage over 30Q/VTC6 ?
I hope they do? But then again, I was hoping for that with the Q8 :FACEPALM: , but Lumintop is better?
Steve's 4 cell GT did pretty poor with the runtime test he did here: https://budgetlightforum.com/t/-/46789/69 - hardly any time in regulation, but like you said, the prototype carrier seemed to have significant loss's, and using only 4 cells, not 8.
Then here: https://budgetlightforum.com/t/-/46789/101, he used 2.0A, not 2.5A and got regulated output for about 50 minutes.
Then here: https://budgetlightforum.com/t/-/46789/101, it shows the improvement of 2.5A to 2.0A for regulation. But this also shows we need to improve the carrier, and that 8 cells should probably make a difference.
No, exactly opposite. 30Q/VTC6's have lower resistance, top performing. Again, it's too early to tell -- we don't have the modified carriers yet, so the theory is correct but we don't know about the changes yet to come.
IMRbatteries.com still has the button top LG HE-4 on sale for $3.50 each. They also have a wide selection of cells at or under $4.00 each. With many top cells even at $5.00.
Ok ! I thought as a buck driver it would act differently (than fet drivers) , thanks for explaining .
4S 18650’s yield 16.8V when charged, so meeting the simple needs of a 12V emitter like the XHP-35 at 2.5A is easily met by virtually any 18650. Especially if using 8 instead of 4.
To meet the needs of 2.5A, even up to 3A, I looked briefly through HKJ’s charts and find virtually every cell I looked at exceeds 3.3V until way out at the end of capacity. I’m having some physical issues at the moment so I didn’t delve into it deeply, but picking what I thought to be the worst cells shows a random bunch of the low end cells easily still do 3.3V way out to end of charge.
I said they’d work, I didn’t say they’d work better or equal to top name cells. Any 4 matched cells will run the GT pretty well, for top performance, you gotta pay to play. 
Well, it's actually over 13V according to DEL, and there was resistances with the carrier that add up, so it's not so easy. It wasn't anticipated it was so high. Could it be the specific XHP35 HI DEL had to test with? Yes - could be, we don't know. DEL himself was surprised.
Yes, it does act differently. It does true regulation like any buck driver as long as the voltage you get from the cells after loss's is at or over what you need -- that's the issue.
Playing Devil’s advocate, here’s a look at actual emitter values in a Shooter 2X with Neven’s LD-2 driver to an XHP-35 HI
0.06A at 10.80V for ~89 lumens
0.55A at 12.22V for ~783 lumens
2.87A at 14.75V for ~2346 lumens
So if the GT were to push 2.87A, which it’s not set up to do, a cell that could stay at that amperage to 3.6V would stay in regulation. This will obviously be lower in a light that has a max capped at 2.5A. If using a lesser cell, simply stay within the ramping confinements, as long as you’re not double clicking for Turbo you’d be fine with any cell out there. Double clicking for Turbo will still work, just not as long or efficiently as a top cell could provide.
Ok, but that's theoretical with no voltage loss's, and, forgot to mention: no driver efficiency loss as well.
And Steve's test results pretty much prove it can't get enough voltage out of 4 cells to keep it in regulation, unless we drop the amps from 2.5A to 2.0A, but with the prototype design and carrier of course.
I wish one of us had an 8 cell prototype to test this all out with. Right now I think DEL is on a long biz road trip though - he would be a big help here. I'm not sure if TA did any tests like Steve's, or if anyone determined where the voltage drops come from that add up, etc. The buck driver is supposed to be pretty efficient.
The testing/analysis might have happened and I missed it, dunno.
Sure would be nice to see some actual test data and specs from Lumintop one of these days?
Specially with the batteries they recommend……
Yeah KW, we asked today if they have test results, gonna post when we hear back on it 
I want one please add me
Put me down for one (1) please.
OK, so here’s to hoping this is a ways off still (for budgetary purposes) :money_mouth_face: This thing is a beast!
I wonder if there is a way to put a usb-c charge port into the cell carriers?
It’d be complicated to do a charging port due to the 4 series arrangement.
It would be pretty useful/cool though…
I just read the first post and realized this project has been going on for about a year. If I’m not mistaken, this was before the TN42 was released. So now the TN42 is out and it is the benchmark to beat. If this takes too long, there will be something better coming out. Hopefully this doesn’t become a cat and mouse game trying to catch up. Kind of like waiting for the next phone “because it’ll be better than the one just released”.