That’s pretty good runtime on max.
Those times exceeded my expectations, and has me wondering if I have over invested in 3400mAh 18650’s as I may start to favour the LiFePO4. Just completed testing the Spark SX5 with the same LiFePO4 AA cell (plus 2 dummies) and got 55 minutes, so I’m presently running it again with 3 AA Recyko cells to see how it compares. The SD52 seems to have a lower cut off value than the SX5, but I’ll have to do it again to be sure. I also tried 2 3v 500mAh RCR123 cells in the SX5 to see if I could subjectively see any difference in brightness over a single 18650 and I could not. Also I planned to get some heat measurements on the SD5 because as I mentioned there were variations but after an hour I couldn’t find my IR thermometer so will do it again when I find it. I’m wondering if it makes sense that the one cell is closest to the operating voltage of the XM-L emitter so the heat from conversion is the least, and boosting the voltage of the NiMh cells would have more heat loss than a more efficient buck converter? If that’s the case then would it be true to say the most efficient way to power the SD52 would be to use a 3.2v LiFePO4 cell?
My experience with the LiFePO4 batteries in 14500 size is that in 7135 kKD drivers they dont supply nearly as much current as a Li-Ion batteries. In drivers that have a 3.6 volt maximum they work very well.
I see, thanks for that.
So I was wondering, when they say the light has a range of 2.4-7.6v, does that simply refer to the regulating circuit they have in the light, and it will regulate the voltage to something fixed like 3.6v, or does it also provide a range of voltage to the emitter? For example if I look at the spec sheet for the Cree XM-L, it looks like it has a range of something like 2-4v? I was trying to figure out, if I put a 2.4v battery pack in there what voltage it boosts it to, because you can see that you get more lumens by placing a 3.6v battery pack in. I had assumed it came down to voltage, or is it more a function of how much current the pack can supply - as I also understand the OHMS Law principle regarding how the circuit requires less current when higher voltage is available may be important to consider here?
sorry bumping old thread, but I kinda need some advice.
I want to try this lifepo4 14500 battery but not sure about the charger. can nitecore i4 charge this cell properly and safely?
thanks 
No, that charger is not made for LiFePO4.
So was there a final verdict on the coolook 14500’s? I was thinking of nabbing a set for my BLF Thrunite Saber. I’ve had no problems so far but would rather not cook the driver and was thinking lower Vin might give better mode separation. I have the WF- 188 charger already.
Hi, long time no see guys.
Just got 6pcs of these batteries from China Taobao. Pretty cheap, it’s just approx usd2.50 for 2pcs. Unfortunately, Taobao is not like your usual DX.com or aliexpress, so probably i could offer no help on any purchases. (as usual, issue is the shipping of batteries, so even China couriers like 4PX/SFexpress is not gonna help, as they need to go via sea, officially and legit way)
I got them for my NERF modified gun, local IMRs are too expensive. 
Hope they are legit. I saw on HKJ’s website cell discharge that they can do 3 amps easily with a capacity of > 500 mAh.
http://lygte-info.dk/review/batteries2012/Coolook%2014500%20LiFePO4%20700mAh%20(Black)%20UK.html
Just to share some more photos (i cannot vouch for its authenticity)
