Been testing some of my older batteries , and about to test some more ..
So be interesting ...
The crap grey ultrafire are like $8/pair, the xtars about twice that or less. The ultrafires are crap to start with, and what's even worse is that they're not consistently crap so it's probably not very safe to use in multi-cell lights. Frankly half-way decent unprotected cell are better.
Ok, here's the TF Flames, 2208mAh down to 2.6V @ 1A constant draw. Same as what old4570 got i believe. I got the later batch as his....so not too bad. From dealextreme.
Of course those Ultrafire cells are usable for some apps, like XR-E lights or even XP-G. The 783mAh one can still be used for stuff like laser pointers etc. I use them for my greenie, they only draw 0.7A. 
And that means i can switch on the laser for about 1hr and 1.3hrs respectively (!!). And seriously you don't use them for 1hr at a time, so no worries.
What the...it's only $4.80 for 5pcs of the Ultrafire 2400mAh shipped!! Re-claimed cells sure are cheap like nothing (cost is gonna be much lower).
I'd advise getting the TF-Flames, and from DX only. At least we know that's a good source. Other sources, it's like lottery. The "best" thing that can happen to anyone, is getting getting a 2208mAh cell, and another at 1356mAh, the user has no measurement equipment, and then you use this in a triple XM-L with no LV protection...like the TF-3T6. heh....
Wrong. Again, I can buy about 8 of them for about the same price as 2 Xtars and I got money that 8 of them will in fact out last 2 Xtar 2600MAH batteries.
I can buy 2 of these for $4.38 factory sealed and delivered to my door. These again are good batteries regardless of what you Xtar promoters are saying. I will run them in more of my lights and compare them to the Trustfire flames. But I doubt I will see any big difference than what I have seen so far. Again, for the money they are the better deal.
So you're buy something that has a catastrophic failure mode at half the price that DX sells them for. And let's be fair here, it's not really half the price since it costly around $2 to ship them to you, so more like 1/3 the price. Good luck.
Well.. If your personal health and safety is it worth.. its on you.. I better pay a few dollars more and will not land in hospital soon ;) .. Interesting most of the "explosion threads" I read where on "ultrafire" batteries... Nobody suggests here to buy AW, Redilsat or other overpriced (but good) batteries.. But the Xtars with Sanyo are very good value... Btw. two ultrafire on your ebay link are ~9.50 shipped... 2 Xtars are 13.50$ shipped... 4$ for a bit of safety and better batteries... Should be a no brainer imho
There is a lot of variability in batches, esp. the gray ones, and there are probably a lot of fakes too. I have some true gray Ultrafires ("Ultrafire" is engraved on the negative plate) and they do pretty well. My Trustfire flames have been good, but I know some people get bad ones, and there are definitely fakes of those too since I have some (which are lousy). I don't regret buying the XTAR's I got in the group buy, but I wouldn't want to spend more than that.
I don't buy batteries off of eBay anymore unless I know the batteries from that seller have been tested. That's 1 battery for $4.38 that you linked to, which is about the going rate. The XTAR's were $13.50 a pair. I wouldn't trust a battery that $3.50 a pair.
Yea I had the wrong link.
I can buy 6 of these for the price of 2 Xtars. And I'll be the first to let you know if I see a problem. They may not be the Rolls Royce of batteries but they will get you there just like a Volkswagen. I may try some of the Xtars later on. But I like these batteries for the price and they seem to take and hold a charge well.
Also we have these additional pts to consider :
(1) XTAR 2600s are purchased from XTAR HK as per paypal transaction reference. There is absolutely no way you can get ripped off. Zero percent. They ship fast, i purchased 3X from them and 3X they arrived in my mailbox within 2 weeks, fastest was 5 working days. For the budget brands, you deal with ebay, DX, MF, focalprice. You play with roulette as the source, even the same source may receive fakes. And if you do not test/measure, you will never know. In that case it's better to stick with the small single cell stuff, ie you will never advance past a point, esp if in the future when there are new emitters doing higher currents. We all know that lights are somewhat hindered by cell discharge performance - basically it is 18650 coz that is where all the R&D going to be. Nobody will give you a true 6AH 32600 even though size would dictate it easily could.
It is really the fakes that are floating around, the ones with using reclaimed cells. So many hundreds of reports around and they have been around for years literally on websites/blogs/CPF/flashlightforums etc. This is not a new problem, and with new flashaholics they will always find buyers. Sellers are interested in profit, and many are not technical. Eg, you can't blame DX for selling 22g worth of Fujik when it says 30g on the bottle, but you can warn others and that is pefectly ok/legal.
(2) Quality of PCB. Their PCB protection is pretty aggressive. In my DD XM-L lights, they cut off when fully charged, even in strobe mode. Prob at just over 4 amps. Sensitive as well. It works perfectly ok when charged to 4.1V in my DRY triple XM-Ls...so it's cool (no real capacity from 4.2V till 4.1V, unless you count approx 30-45 seconds runtime as capacity). Low voltage cut also works. This would be a very safe battery to use but still leave enough headroom for high powered lights. I have many other budget type protected cells but they cut way too early like they do not allow me to use in the UF-980L @ 3.5A. Only exception is Trustfire Flames.
I don't know how they protect against overcharging in case your cheap charger goes wonky (most usual case of catastropic venting), but i'll bet they cut perfectly. If a user wants to save a few bucks on cells, i am sure they won't be using hobby chargers or Pila or even XTAR. I already have 2 faulty OEM generic charger, one actually works but cuts at 4.25V and i don't like that. Try some more with cheap cells w/o PCB and play more roulette....
I'd rather run a 4S light complemented with equipment like DMM/charger and Li-ion handling SOP, its relatively safer....
(3) Unprotected. Esp if you are a novice and do not know when and how a driver fails and FETs create a dead short and what are the consequences, you will definitely be facing a pipe bomb case, guaranteed. Even if it's protected. I have a protected cell actually do not protect against shorts, faulty? Again, it's roulette. Obviously if they can fake a cell they can also fake a PCB. I'd not count on it to work 100%, or prolonged usage etc.
Edit - i am not saying that they are bad, but only for other applications with lower current needs.
If it's too technical, this should explain better.....pictures and video.
http://www.youtube.com/watch?v=mw8jb1KmAG8
http://thebrightsideforums.com/viewtopic.php?f=15&t=201
Here's one with the Ultrafire Grey...
http://www.candlepowerforums.com/vb/showthread.php?318976-OMG-i-nearly-lost-my-finger!!
http://www.candlepowerforums.com/vb/showthread.php?280909-Ultrafire-18650-3000mA-exploded
During usage : http://www.candlepowerforums.com/vb/showthread.php?122500-Cyclops-Flashlight-Explosion
Seriously when i discharged mine at 1A it already got somewhat warm (high internal resistance). I don't know how it can survive a 2.5-3A discharge and also heated by the XM-L, and still stay safe. Not to mention those DD lights (pretty common) soaking 4 amps which the battery can do at full charge. (at least mine does, even though the capacity is sucky)
I have a lot of flashlights, and I can't see putting Xtar batteries in everyone. So what's the cheapest route you feel is still a good enough battery? Someone mentioned the Hi-Max. But even www.goinggear.com sells the Ultrafire blues and I think some of their lights come with a charger and these batteries. And they aren't protected. But apparently they work ok or I doubt the guy would still be selling them. Go to youtube and you can see tons of his flashlight reviews. Seems to be a pretty smart man on flashlights.
The hi max are good, but not that much less than the xtars anyway. I mean, if you wanted protected cells, $7 apiece for high end stuff really isn't all that much. You don't need every light to be loaded, you'll only need a few for normal use anyway.
So where is the cheapest place to buy the Xtars? Like I said I may buy a few and try them.
Search the forum. At least two vendors were offering them at the prices mentioned above.
We have here a proverb. Hard to interpret directly but:
Always buy the cheapest. By the time, it will cost you a lot and expensive means good quality!
Pretty much fits this thread like a glove...
Well I'm not pitching the Ultrafires I can tell you that. They will do me for now.
I purchased 3 sets of grey UF batteries in the beginning.
They all ended up having different buttons, PCBs, printing, and capacities.
Not wanting to lose a finger, I only buy Sanyo- or Panasonic-based cells now.
Ok men I just bought 2 Xtar 18700 2600MAH batteries for $13.50. That is a very good price for some great quality batteries. So I thank you men. I'll probably buy some more.
Thanks Serena for still honoring that price.
I'll let you guys know what I think once I get to use them. I'm sure they are as good as you guys say they are.