I got these cells because they look interesting and are only a dollar each. I don't really know what their best use is though?
I have the TrustFire TR-001 which I really like, and a Universal Smart Quick Charger
LiFePO4 needs a different charger. I can't say off the top of my head what the charging regime is. It is supposed to be impossible to make them go boom but the voltage and capacity are lower. The better power tools with lithium packs use these as they will withstand cruelty far better than lithium ion cells and will tolerate very high discharge rates and higher than lithium ion cells. The high-power incan guys use a lot of these.
Having checked, I'd not recommend using a standard lithium ion charger - they charge at 4.2V, the recommended charge voltage is 3.6
Since the 123 cells are supposed to be pretty robust, you'd probably get away with charging them in a 4.2V charger but at the cost of never getting to the constant voltage charge and you are going to have to watch a voltmeter. You should be able to get them to 70% charge that way.
I have seen a video of LiFePO4 cells being shot up without doing Bad Things - lithium ion cells do Very Bad Things when you abuse them like that.
Don't charge at 4.2V. There are some chargers that work, for example http://www.kaidomain.com/ProductDetails.aspx?ProductId=6651
I did some testing of it here: http://www.candlepowerforums.com/vb/showthread.php?267231-HUANGAO-HG-1210W-charger&p=3346213&viewfull=1#post3346213
I own and use both of these successfully.
The UF-138 has a switch which is supposed to give it the ability to charge either LiCo or LiFePO4 cells. My copy only charges LiFePO4 cells to about 3.3 volts. It charges LiCo cells to about 4.2, depending on the condition of the cell.
The Jinlong charger only does LiFePO4 cells and seems to do a nice job with them. Mine charges RCR2 and 16340 LiFePO4 cells to about 3.55 - 3.6 pretty consistantly.
I've just bought one of these http://www.dealextreme.com/p/ultrafire-wf-188-rapid-charger-for-3-2v-3-7v-lithium-batteries-100-240v-44091
It comes with a US plug, but supports 240v. So I should just be able to cut the plug off and replace it with a UK one.
It's just a shame there isn't a world standard for plugs...oh and it should be the UK one as it's just much more sensible :)
They use a standard figure "8" appliance plug. Any decent electrical store should have those.
4Sevens Charger! Charges both to 4.2 and 3.6 volts, CC/cv.
No need to cut it off, just order one of these for 89 cents http://www.dealextreme.com/p/flat-to-round-power-plug-convertor-3529
Bah! Why didn't I think of that. The one that comes with it isn't a normal "8" as one side is square, a normal "8" plug does fit though :)
While a lot of Europe does use those we don't in the UK, our plug look like this (image from wiki)
I've got a converter plug, but they never seem to be terribly reliable - the US/EU plugs just fall out or only work at the right angle.
Anyway problem solved :)
I got mine yesterday too! :D And I've been using the same charger! LOL
Yeah, I've been having problems with these. I've taken some photos and measurements for review purposes, but contemplated starting a pre-thread for questions... you beat me to it.
First, mine came all charged around 3.3 volts.
Second, my 'universal charger' has charged LiFePO4 CR2 cells from DX just fine. I love that little universal charger, and it stops charging those rCR2 cells at exactly 3.8 volts. That may be too high by some estimations, but I think they can be charged higher. And they seem to work fine. It's about the slowest charger you can buy, although charging at 4.2 volts might be considered high.
Enter these "a123". I have a few problems just with 'words', before getting into the batteries.
Ebay category is "Lithium Ion", but in the auction body they describe them as LiFePO4. Perhaps Ebay doesn't have a correct category. However, they also describe them as A123, which according to some just-now web searching, is apparently neither, but Lithium Ion Nanophostphate.
Quote from an electric remote-controlled airplane forum at
LiFe is just the abbreviation for "Lithium" and "Iron". Technically they are LiFePO4 or "Lithium/Iron Phosphate". Both the LiFe batteries and the A123's have exactly the same chemistry and voltages but the genuine A123 is built with a patented nano phosphate process and they can put out 3 to 4 times the amount of power you see in an LiFe.
They work well for rx packs but there have been issues with QA on the LiFe batteries so make sure you get them from a reputable vendor or just go to the genuine article. Chargers with either an "A123" or "LiFE" setting can be used for either battery, do not use a "Li-Ion/Li-Po" setting on a charger for these batteries since as previously noted, those run at higher voltages.
An Li-Ion battery while safer than a Li-Po and with identical voltages, cannot put out anywhere near the power of the other three types of batteries and take much longer to charge.
The chemistry (at least the term LiFePO4) appears nowhere on the battery wrapper, nor is there information about minimum and maximum charge voltage. In fact, the batteries DO have "A123" written right on the wrapper... which, if the above is true, is a lie. Funny enough, each cell appears to have its own serial number! Fancy that. BTW, I ordered what I thought were 2 at $2/apiece, and got 4--were they $1 apiece like the OP wrote? The buy-it-now was for $2, and the listing states 1 piece. I'm wondering, did I just get lucky, or are they so bad they shipped 4 to try to butter me up or 'bribe' me to not leave bad feedback?
Okay, so then the Ebay 'auction' claims the finished charge voltage is 3.65 ("3.3V nominal"). Well...
My cells are refusing to charge past 3.3V. In fact, I think I damaged my first cell beyond usefulness. I left it in my puny charger for about 5 hours. The light was green by then, and I don't know how long for. I know my li-ion 18650's take overnight to charge even from partial discharge, so I figured 5 hours wasn't overshooting. Stupid thing measured 4.1 volts! I thought they'd shipped me li-ions... then, I noticed I couldn't get a reading on the cell. Voltage was jumping around all over the place, occasionally coming back to 4.1. I put it in a flashlight, and while it lit, it flickered with any movement (or perhaps even without), which of course changed modes each times (this is really annoying with a blinky-mode driver).
Okay, so I vowed to charge my 2nd cell much shorter. Put it in a 3.27 volts. After an hour or so, I took it off the charger (wasn't even warm, but cells never get warm in that charger). Only read 3.33 volts! I remembered that all 4 cells came right around 3.3 volts, and were probably freshly made. I began wondering if this chemistry peaked out at 3.3V, despite what the listing said. So I started researching "LiFePO4" and "3.3V" as well as "3.0V nominal", because I assumed that's what they would be. My search didn't really yield such a cell. Just people arguing about what the final charge voltage should be of a LiFePO4 cell (arguments ranged from 3.3V to 4.1V).
So I decided to do a runtime test of my second (hopefully not overcharged) cell. Due to the low voltage, they would not light up my single-mode/single cell (direct drive) XR-E R2-bin drop-in. They did, however, light up my XM-L drop-in due to its lower Vf (forward Voltage). XP-G's should have a similar Vf.
Well, my runtime test got kinda messed up when I accidentally shorted the battery thinking I was testing the voltage, when I was really testing the amperage :D . Yeah, my DMM beeped at me and showed 16 amps 
. I was on the phone with a friend at the time, which was the reason for my distraction. So... duh... I did it again and got the same beeping, LOL. Then realized what I had done, and measured the voltage... I think it was down to 2.7V. Good thing they sent me 2 extra cells! How did they know?!
So back into the charger it went (I've been charging these EVERY time in my fireplace with the door closed, by the way). 20-30 minutes later it was back to my pre-shorting voltage, which technically ruined my test (and maybe the battery), but what they hell, I stuck it back in the flashlight and continued, and then biffed my timer. But I estimate I got about 20 minutes of "High" out of my Manafont Ultrafire XM-L drop-in before it started dropping rapidly. While it was on, it drew 3.5 watts on High (compared to 10+ with a Lithium Cobalt cell). However, the light output was very respectable in comparison to the 10 watts. So, I (very) roughly estimate that I got about 60 watt-minutes (~3W x ~20 minutes), which should be 1 watt-hour, or 1000 milliwatt-hours? Whereas a 2500mAh li-ion 18650 battery would be 9 watt-hours (2.5Ah x 3.6v nominal). Need to do again with a non-damaged battery. But preliminary suggestions could be that they have capacity similar to a 14500 li-ion cell.
So now, I'm left wondering what the deal is with these cells. Or, at least problematic if they won't charge beyond 3.3V. Anyone get them past 3.3V with any charger? What do they really charge to?
After having been quite impressed with the cheap DX rechargeable CR2's, so far I'm hating these cells. I don't know what I should expect, but kind of like Han Solo walking inside the belly of that asteroid monster, "I've got a bad feeling about this". Between the Big Bird yellow, the ambiguity or falsehood of the wrapper, basketcase behavior in my puny charger, and refusing to charge past 3.3V (though since the 1st cell, I haven't pushed it much)... so far I'm glad I only dropped a several dollars. Then again, I didn't know if I'd be kicking myself for not having bought more if the price went up.
BTW, the cells came extremely well packed. Lots of bubble wrap. And quicker than expected.
When those cells are fully charged, they rest at 3.3V. You can charge them until the cows come home and at whatever voltage you think you want, but they'll always bleed off the excess and return to 3.3v. It sounds like they are just not for you.
I ordered 1 cell at the stated price of 1.99 and received 2 of them instead, so I guess they didn't know what they were doing. It states in the description these are 1000-1100 mah which agrees with my other research. I guess these aren't really ideal for flashlights running at normal wattages, but more for extreme builds pulling 5+ amps with cells in series. These are most likely real LiFePO4 cells but probably not real a123. They look like they are pretty high quality though.
The seem more suited for running electric motors like in RC cars, RC airplanes, electric bikes, etc. btw the description states 3.65 v as max charge voltage.
These are much safer than normal lithium ion-I'm considering taking two of these and putting them in a Mag 2C with a Fusion 36.
I hooked a cell up to my hobby charger to get some mAh readings. I received the cell at 3.21 volts, and my charger took it up to 3.48 volts with a total of 807 mah put into the cell. I just took another reading ~72hrs after charging and it only has sunk down to 3.46 volts. I am a little suprised that it took over 800mah, as this cell is only advertised as 1100mah total capacity. BTW these cells are still being sold for less than 2 dollars a cell