So we know about LiFeP — lithium ion phosphate cells.
Nominally 3.2v.
Extremely flat discharge curve until the last few percent
Thousand rather than hundred charge cycles before the chemistry gives out.
Many other advantages, including — doping with Yttrium (“Y”)
Where can one get these new variety cells, other than in large quantities from solar energy suppliers?
ordinary LiFePO4 cells can be rather
“biiiiiig and roooound” as Dilbert’s Dogbert would say …
http://www.evassemble.com/index.php?main_page=index&cPath=2
and on the same page lower down, the LiFeYPO4 cells are bricks.
Looks like you could just use the cell itself as the base of the flashlight — two wingnuts to attach the driver and light head, and off you go …
Interesting link, I didn’t realise they made LifePO4 cells in those sizes for ebikes and the like, very interesting prices as well. Those cells are proper beasts too, shame they’re slightly too big even for my battery pack.
I’m actually re-contemplating a switch to this chemistry (although in a 3s softpack intended for rc use) exactly because of the very flat discharge curve and convenient voltage. A standard 2s lithium source can very quickly drop out of regulation in lights driving 6v leds at high amps and with higher resistance losses or linear drivers such as 7135s.
These cells with 3s delivering 9+ volts over a long period of time sound very usable to me right now. 
-
Hmm, wonder if a 6v mt-g2 would survive being direct driven by the brief 10.8v of a freshly charged 3s liFe source? Maybe the 9v variant would be a perfect fit for DD and 3s LiFe. 
rovert applied 3s1p AW 2000mAh IMR cells in a carrier to a de-domed 6v MT-G2 througha BLF17DD over here: rovert - Convoy L2 Mod
Tint shifted but it didn’t die.
I’ve been looking to get one for my car but they still are a bit too expensive.
Wonder why there is such big difference in size and weight between these two?
http://www.evassemble.com/index.php?main_page=product_info&cPath=2&products_id=35
Is it not because the Winston is using the less mature LiFeYPO4 chemistry rather than LiFePO4 like the Shorai?
Just did some quick reading and it seems the Yttrium doping (LiFeYPO4) is better but there is not much difference in size and weight.
Shorai is using an inflated Ah rating to “better” compare to lead acid batteries though, their 36Ah battery is actually using 12Ah cells 
I have a 16P4S pack made out of 2300 mAh 26650 A123 cells. Short circuit current is over 3200 amps… I’m thinking of building a 40,000+ lumen light light using it.
One should not deplete a lead acid battery completely, destroying it that way. So the “really usable” capacity of a 36Ah lead acid battery is comparable to a 12AH LiFePO4 battery, which may be depleted completely without destroying it.
[edit]
BTW: I have lots of 14500, 18650 and 26650 LiFePO4 batteries and use them in place of normal LiIon. I love this chemistry because of their good nature regarding abuse and especially the bigger ones from A123 are able to deliver massive amounts of current without major drop in voltage.
How did you measure that?
Cheers David
Yes you are right, I just found it a bit sneaky that the aren’t also posting the true capacity.
Think I will try one of these instead http://www.ev-power.eu/LiFeYPO4-batteries-12V-1-1/Lithium-Battery-LiFePO4-12V-20Ah.html?cur=0
I have measured the short circuit current of those cells at over 200 amps. With 16 cells in parallel you get 3200 amps. And probably a bit of smoke. And sparks. I do have a current probe that can handle 5000 amps. J)
Another option for the light may be 4x20,000 lumen Bridgelux arrays instead of just two. So maybe 80,000 lumens.
Thanks UliBär — I’d love to see a summary/review of the sources where you’ve found these — and your experience with the cells you’ve been using.
Recommended charger?
I got the bigger (18650, 26650) cells from here: LiFePO4 Akkus | akkuteile.de
and the tinier (10440, 14500 mostly Soshine, Coolook, etc.) cells from dx.com and other vendors of *bay, before HK-Post decided to not further deliver Lithium batteries… 
If you can get them, the LiFePO4 cells from Tensai are awesome, although a little costly, at least here in Germany.
For charging the bigger ones i use the following chargers:
http://www.ebay.com/itm/251772348112
http://lygte-info.dk/review/Review%20Charger%20Soshine%20H2%20UK.html
For charging the smaller ones:
http://www.ebay.com/itm/261715639693
Reviews from HJK:
http://lygte-info.dk/review/batteries2012/A123%2018650%201100mAh%20(Yellow)%20UK.html
http://lygte-info.dk/review/batteries2012/A123%2026650%202500mAh%20(Green)%20UK.html
How about a carbon arc lamp?
Thanks for the correction! Interesting stuff.
Assuming 12Ah for the Shorai:
|
The Shorai weighs 2.25kg w/ a volume of ~2215 cubic centimeters. |
~1.0g per cubic cm |
~5.4mAh per cubic cm |
~5.3mAh per gram |
|
The Winston weighs 8.3kg w/ a volume of ~5850 cubic centimeters. |
~1.4g per cubic cm |
~6.8mAh per cubic cm |
~4.8mAh per gram |
That’s all very rough math. Especially once you consider that I’m not taking the terminals and things into account.
…
I’m increasingly interested in these.
Anyone know a retail seller?
A123 has 26650 and 18650s: http://www.a123systems.com/lithium-battery.htm
I have a few of these 18650 a123 pulls from fasttech: http://www.fasttech.com/products/0/10002801/1208601-a123-systems-18650-lifepo4-1200mah-high-discharge
But they were a better deal before shipping became a pain. Ebay also has some too.