I got a pair of these batteries last week and put them through their paces this weekend. I had heard these were better than a lot of other batteries and was impressed. They definitely seem better than my other 18650's but I don't have a huge number to compare against. There are more extensive and scientific tests elsewhere, including here:
I tested them in the following lights, measuring the voltage of the battery every 15 minutes until it was 3.6V or less. If the voltage was getting close to 3.6V sometimes I would start measuring every 5 minutes, so not all of these durations are in 15 minute increments. With one exception the flame Trustfires seem to last about 20% longer. In the first test they were 37% longer than the Ultrafires and more than that over the gray Trustfires.
Light
Gray Trustfire
Gray Ultrafire
Flame Trustfire
504B XR-E R2
stock driver
1:45
2:00
2:45
502B XP-G R5
AK-47 1050mA driver
1:25
1:50
2:15
504B XP-G R4
Shiningbeam 1400mA
1:00
1:10
1:25
WF-1200L P7 (2 cells)
stock driver
1:00
1:15
1:30
Length of cells (mm)
67.08, 67.33
67.81, 67.91
68.20, 68.27
I also included the length of the cells. Although these cells are longer than the others, they fit in all three of the 18650 hosts I have.
If you need 18650 cells, these seem like the ones to get, though they cost more than the gray ones. If you don't care about a little extra runtime and want to save a couple of dollars, the gray Ultrafires might be the way to go.
In case anyone hasn't seen thishttp://candlepowerforums.com/vb/showthread.php?t=257543 also showed good results for the black flame Ultrafires as did http://www.kansai-event.com/kinomayoi/battery5/Li-ion_2009.html although in that one the pink Ultrafire "2600mah" came close (interesting it looks like they've gone up in price since the Japanese review) & http://www.candlepowerforums.com/vb/showthread.php?t=257543&page=2. The grey Trustfire seem to biggest lottery, some got quite good batteries but some are quite crap. See also http://www.dealextreme.com/details.dx/sku.5776 I also read a few people claim in DX the blue Trustfire have gone down in quality since they went down in price (they're now not much more then the greys but also perhaps no better in quality). I also came across a blue disambley pic if anyone is interested
Bear in mind most of those batteries in reviews I linked were purchased the end of last year or so. And of course those are only testing capacity usually with fairly new cells, how they hold up over time (in particular how they compare) is anyone's guess.
But anyway yeah the black flame Ultrafires seem a good bet for resonably cheap cells with good capacity. Whether it's worth it over the cheaper ones well that will depend on the invidual (the price difference is about 25%).
I purchased a Ultra Fire Wf 139 & 4*18650,the problem is the charger cuts at 3.84v, in each cells,green led status for more than +5hrs or so but still the voltage is 3.84.Can any one tell if the charger is bad or all the cells.
In the meantime I contacted Dx & they are ready for giving replacement or store credit,but I somehow feel what if the new batch of Wf-139 chargers are all undercharging or perhaps the 4*Tf Flames what I got are all defective ones,any one reads this post plz reply and give opinion whatever in ur opinion.