# Lithium Ion testing



## Wirecutter (Jul 26, 2007)

I think I'm turning into a battery geek. I decided to do a little research, and I got myself a battery tester. I put together a few little packs, and started running data.

So far, I've been testing 2200 mAh and 2600 mAh 18650 cells. Pretty small time stuff so far - a few packs have only two cells, but the ones I've got the most data from have 4 in series.

I'm running a test at 1C right now, so no results yet. But I ran tests on two particular packs. Summary: (the first number is rated capacity in mAh)

2200 x 4 cells, EOD at 11.2v at 0.5A rate: 2.1 Ah
2200 x 4 cells, EOD at 11.2v at 1.0A rate: 1.83 Ah
2200 x 4 cells, EOD at 11.2v at 1.0A rate: 2.1 Ah (same pack, next day)
2600 x 4 cells, EOD at 11.2v at 1.5A rate: 1.23 Ah
2600 x 4 cells, EOD at 11.2v at 1.5A rate: 1.23 Ah (same pack, later that day after recharge)
2600 x 4 cells, EOD at 11.2v at 2.0A rate: 1.77 Ah
2600 x 4 cells, EOD at 11.2v at 2.0A rate: 1.75 Ah (same pack, next day)

First thing I'm noticing is that I don't get stated capacity. I'll post more data if anyone's interested, but I'm in a bit of a hurry at the moment. Basically, I don't think it's the fact that I'm not discharging enough. When the pack reaches the 11.2v level, the discharge curve has gone into a steep dive, and it's pretty obvious that continuing on will provide little or no benefit. Going beyond that point sure seems like battery abuse to me.

Anyway, I'm busy collecting data, but this battery tester is cool. It takes a sample once per second, and puts a constant current load on the pack. It graphs the data nicely, and can export to csv files so I can graph and analyze to my heart's content. The data are a bit disconcerting, however. It confirms my suspicion that battery makers, (at least Sa****g and Te***gy) are swinging a bit wide with specs.

By way of background: These are 18650 lithium ion cells. The cells are connected with nickel strip using a stored energy resistance welder (Unitek 250), a proper weld head, etc. Each pack has a protection circuit that monitors all cells and disconnects the pack in the event of over charge or over discharge of any cell. I've only seen the protection kick in once, but that was on that steep downward dive of the voltage, so it should have. Essentially, the packs are made just like the commercially available stuff, except I don't have quite as much smarts installed as say, a laptop pack.

I know it's not much info, but can anyone shed light on obvious stupid things I'm doing wrong? I want to get this right before I work with more expensive batteries.

-Mark


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## MN Driver (Sep 29, 2009)

The Ah ratings that you are getting from your tester may be accurate. If these cells are the Te***gy cells then based on what I've read on other forums regarding their NiMH cells, they didn't just overrate the capacity by a factor of 10-20% based on the testing of those who bought them and wanted to use them, they also didn't pull promised continous amperage draw without a really bad immediate voltage drop that made them useless for the e-bikes people bought them for. It seemed that it took 3 or 4 strings in parallel to get them to provide the proper amperage level to keep the voltage high enough for them to be useful.

I have a feeling you are doing things right, although you didn't mention your charging profile. Typically with Lithium-Ion and LiPo are charged holding them at 4.2 volts until the charge amperage is somewhere around 3-10% of its original charging amperage. I'm sure C/20 would be good. What I don't understand is why the 2600's gave you more total energy output with a higher amp draw, that is something I know I can't identify unless it's a typo.


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## IamIan (Mar 29, 2009)

that sounds like a CBA-II or a CBA-III battery tester... or it is a different type?

The better battery testers let you celebrate to account for the resistance of the leads and such which if not done can result in inaccurate voltage measurements.... I know from personal experience the CBA-II and III have this as one of the extra features.

Here is some advise I will share about battery testing that I've picked up.

Remember the chemical reactions in the battery are slower than the electronics.

What that means is... You might want to give the chemical reactions in the battery time... unless you are trying to test them for that kind of rapid cycle.

In a nut shell after a battery has been discharged or charged give it at least 5 to 10 hours to stabilize before moving on to the next step... so if you charge it, give it 5 to 10 hours to stabilize before running the discharge cycle... after discharging give it 5 to 10 hours before the charge cycle... etc... unless you are specifically trying to test the results of fast turn around cycling back to back.

Slower charge and discharge cycles will always yield more into and more out of a battery... that's just chemistry ... record / save your results ... in the CSV format you can just import them into a spread sheet like Excel or OpenOffice and make a ton of data allot easier to follow and see the trends.

-----------------

I'd be interesting in additional detail if you are inclined to post it.

But I have been a battery hobbyist for several years and it my kind of thing.


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## Wirecutter (Jul 26, 2007)

Sorry, not a typo. It had me scratching my head, too. 

I've got a buddy who is into RC in a big way. With a nickel-based chemistry, many cells will put out more peak amps if they're charged with a "hotter" profile (more amps, regulate by temperature), based on his experience. Of course, you don't want to mess around with the charging profile of lithium cells. I suppose if you were an expert, you'd know what to tweak and not to tweak, but I have no claim on expert.

I'm still running data and trying to figure out what it means. Back later.

-M


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## Wirecutter (Jul 26, 2007)

IamIan said:


> that sounds like a CBA-II or a CBA-III battery tester... or it is a different type?


 You're exactly right, it's a CBA III. I might just get an additional one, because I'm keeping this one pretty busy just now. I also want to screen the AGM batteries on my gokarts, and at a max of 150W, that'll take a while.

I've also got BK Precision electronic loads designed into the testsets I code professionally, but I'm not inclined to drop that kind of cash into this project just now. The BK's will do all of this and more, but at 10x the price. The CBA III was at the right price point to keep me from designing and building my own system.

I wish the CBA would record .csv (and even graphs) automatically by default, but for the money, I can't really complain too much. I'm sure it will improve with subsequent revisions of firmware. In the mean time, I know how to drive a spreadsheet. 

-M

PS: nothing proprietary about my data, I just have to format it and get it posted. Soon.


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## Amberwolf (May 29, 2009)

I'm definitely interested in this data, because if things work out right, I'm going to end up with a few hundred 18650 cells, mostly by Sanyo and some by Sony, to build my ebike packs out of, to replace or enhance my SLAs. 

Are you testing any of those brand cells, by any chance? The Sanyo are UR18650F, I think it is. Don't know the Sony ones yet.
________
THAI GIRL LIVE


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## Wirecutter (Jul 26, 2007)

Ok, the attachment is the raw data. The files themselves will indicate the voltage, cutoff, etc, etc. Samples are taken once per second until the voltage cutoff. File names in the zip are of the form:

[Te | Sung][rated capacity in mAh]x[cells in series]_[discharge current]_[date].csv

so the file "Te2600x4_2r6A_26Oct09.csv" is a pack of 4 Tenergy (Sung = Samsung, btw) 18650s rated for 2600mAh that were discharged at a 1C rate of 2.6A yesterday afternoon. I used the nomenclature common in component marking where "r" signifies a decimal point, so "2.6 amps" is encoded as "2r6A".

The rest should be obvious, and I'll post more info as it is developed. Yeah, I know I didn't include any "apples to apples" tests where the respective vendors' cells were tested at the same discharge current. I'll gather up some of that, too. The only real comparison is the "1C" discharge rate tests, where the Samsungs were 2.2Ah and the Tenergies 2.6Ah.

-Mark

PS. Yeah, note the dismal performance of the Tenergy cells. The 2200 Samsungs actually showed consistently higher capacity at various discharge rates than the 2600 Tenergy cells of the same physical size.


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## samborambo (Aug 27, 2008)

Wirecutter, are these brand new cells? It looks like they're gaining capacity with successive charges which would lead me to think that they're being broken in. Lithium cells often need at least 20 cycles before they show their full capacity.


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## Sunking (Aug 10, 2009)

samborambo said:


> Wirecutter, are these brand new cells? It looks like they're gaining capacity with successive charges which would lead me to think that they're being broken in. Lithium cells often need at least 20 cycles before they show their full capacity.


I may be wrong, but FLA chemistry are the ones that need cycled 20 times to achieve full capacity. Lithium is at max capacity when manufactured, and start decreasing immediately after manufacture.


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## IamIan (Mar 29, 2009)

Wirecutter said:


> I wish the CBA would record .csv (and even graphs) automatically by default, but for the money, I can't really complain too much.



I'm in the same boat... although I have been tempted by the CBA amplifiers as well.

Have you already done the calibration for dV due to the resistance of the wires leads?

Have you already done the current calibration fine tuning?

Have you also used the charging monitor/logging function yet?


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## samborambo (Aug 27, 2008)

Sunking said:


> I may be wrong, but FLA chemistry are the ones that need cycled 20 times to achieve full capacity. Lithium is at max capacity when manufactured, and start decreasing immediately after manufacture.


Would you mind correcting the Wikipedia page on that then?

http://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery 

_"A break-in period of 20 charging cycles is currently recommended by some distributors"_

EDIT: The same bullet point also states that the cell can be damaged if cycled to more than 66% DOD before the cell is fully broken in.


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## Amberwolf (May 29, 2009)

That is one of the common things with ebike batteries for LiFePO4; probably LiPo as well. Some people have actually damaged their packs permanently by not "breaking in" the cells slowly. 

It's part of what I expect to have to do for the cells I'm getting.
________
HOW TO ROLL BLUNTS


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## Wirecutter (Jul 26, 2007)

IamIan said:


> I'm in the same boat... although I have been tempted by the CBA amplifiers as well.
> 
> Have you already done the calibration for dV due to the resistance of the wires leads?
> 
> ...


I haven't done any calibration, but I'm using pretty short, fat wires and good connectors. I think at the current and voltage levels I'm working at, it's not a significant factor. This thing records with 10 bit resolution, and only goes as low as 100mA load.

I haven't gotten into charge monitoring yet. Is that in the basic software package, or do I need to upgrade?

It looks to me like the software has a lot of room for all kinds of slick new features. First thing I'll probably want to do is get more than one of these things running on the same computer. Apparently, that's coming Real Soon Now.

The cells in the posted tests are all brand new. I've got quite a few other cells from otherwise busted laptop battery packs, and I want to screen those. 

I've already done a little screening. Some of the cells are pretty decent, giving up to 50-75% capacity, and some are just awful. I've learned that many of these packs will fail for reasons other than end of cell life. They'll also fail when just one cell goes loopy, with the rest of them still in good shape. Then there are fuses and such, and processors that monitor and record things like total power in and out, number of cycles, etc. Some people believe that Dell packs will decide to fail automatically after a certain number of cycles. I know that the battery packs are technologically capable of this, but it sure would be a slimy thing for a company like Dell to do. (After all, their business is supposed to be computers, not batteries. Where would they be if their products developed a reputation for poor battery life?) Personally, I'm not a conspiracy theorist, and I simply don't buy laptop battery packs. My company does.

Anyway, for right now, I'm just collecting data and trying to determine which battery makers are the real deal and which are full of spit. I'll make my data available, too.

-Mark


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## Wirecutter (Jul 26, 2007)

samborambo said:


> Would you mind correcting the Wikipedia page on that then?
> 
> http://en.wikipedia.org/wiki/Lithium_iron_phosphate_battery
> 
> ...


 The same bullet point also has the tag "citation needed" attached to it. I'd like to hear more about the need to "break in" lithium cells. For the record, the chemistry I'm using is the traditional LiCoO2. I've been under the impression that these cells are born in "ready to use" condition, provided one is careful not to abuse them.

Another interesting thing in this Wiki entry (subject to change, of course, as Wiki pages do...) is under the Specifications section.


> 100% DOD cycle life = 2,000-7,000 (Number of cycles to 80% of original capacity)


 Here I thought that nearly any battery, especially a lithium-based chemistry, is *completely ruined* if you manage to get it 100% discharged. In fact, I can't think of one that isn't essentially trashed before you can even reach 50%. I'm obviously misunderstanding the "100% DOD" term. That must mean 100% of the normal "you're done" discharge level, which is really something like 80% charge. Looks like I'll have to do some more research before I know what I'm talking about.

-Mark


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## hardym (Apr 2, 2008)

Just to be clear, 
for Lithium Ion Phosphate , 100% depth of discharge (DOD) is when the cell reaches it's low voltage threshold, usually specd to be aroudn 2.5 V.

It is not well known but the TS LiFePo4 manual suggests a sorta 'format' for a new battery, which is to charge completely up to 4.2 and hold it there for a couple of hours (doesn't take much current to do that).

Max capacity should be just after formatting.

Not sure if formatting helps, but the batteries are too expensive to not follow the directions.

Mark


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## MN Driver (Sep 29, 2009)

Wirecutter said:


> Here I thought that nearly any battery, especially a lithium-based chemistry, is *completely ruined* if you manage to get it 100% discharged. In fact, I can't think of one that isn't essentially trashed before you can even reach 50%. I'm obviously misunderstanding the "100% DOD" term. That must mean 100% of the normal "you're done" discharge level, which is really something like 80% charge. Looks like I'll have to do some more research before I know what I'm talking about.
> 
> -Mark


State of charge and depth of discharge are a function of Ah(amp-hour) capacity, not voltage. The capacity is measured within a safe voltage range so 100% depth of discharge would be when all of the usable capacity has been used, over 100% would then likely cause cell damage. The shallower the depth of discharge the more total cycles you can get out of your cells. Thunder Sky for example claims to give 5000 cycles at 70% DOD and 3000 cycles at 80%. So it is apparent that to get the most out of your pack you would want to leave 30% of wiggle room, which is beneficial in an roadable automotive application because we don't run into the same conditions every day so in case one day you are forced to take a detour because a road is closed and you are driving through the rain with the wipers, lights, defrost, and heat on you can be more confident that you can make it back.

With the 50%, could you be thinking of voltage? If that is what you were thinking of, then yes, lithium batteries will be damaged if run below 2 volts, but even that is far lower of a voltage point than any usable capacity amount so it really should never get anywhere near that low, usually there is a rapid voltage drop at 3 volts down to the bottom for LiFePO4.

Another note, open circuit terminal voltage on a cell doesn't indicate state of charge accurately anywhere other than at the very high end and low end of the state of charge.


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## samborambo (Aug 27, 2008)

Wirecutter said:


> Here I thought that nearly any battery, especially a lithium-based chemistry, is *completely ruined* if you manage to get it 100% discharged. In fact, I can't think of one that isn't essentially trashed before you can even reach 50%. I'm obviously misunderstanding the "100% DOD" term. That must mean 100% of the normal "you're done" discharge level, which is really something like 80% charge. Looks like I'll have to do some more research before I know what I'm talking about.
> 
> -Mark


100% DOD is defined as discharge down to the cut-off voltage.

LiFePO4 is different in many respects compared to other Li-ion chemistries. The physical volume of the electrodes in LiFePO4 is very stable over the cell's charge cycle compared to Li-ion, hence when fully discharged very little mechanical damage is done.

LiFePO4 beats other Li-ion chemistries in every respect except energy/weight. They have a high power density, are cheap and will last at least 5 times longer than other Li-ion.

Are these cells intended for an EV conversion? What's your reasoning for using LiCoO2 instead of LiFePO4?

Sam.


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## Wirecutter (Jul 26, 2007)

samborambo said:


> 100% DOD is defined as discharge down to the cut-off voltage.
> 
> LiFePO4 is different in many respects compared to other Li-ion chemistries. The physical volume of the electrodes in LiFePO4 is very stable over the cell's charge cycle compared to Li-ion, hence when fully discharged very little mechanical damage is done.
> Sam.


Sam -
Then which lithium chemistry is the one in which the cells need to be in a rigid case to keep down on expansion? Not LiFePO4?

I've been considering these (or at least, this chemistry) for eventual use in an EV, mostly because of the energy density. Yes, I want to go fast and light, and yes, I know I have to be careful how I implement many things about it. I'm definitely not committed to any one chemistry just yet, though.

I kinda figured I was misunderstanding the DOD term, and I shouldn't confuse "charge" with "cell voltage". It makes perfect sense now. It also makes perfect sense if you look at the data and plot the curve. In every test I've run, there's a very distinctive "knee" where the cell voltage takes a dive. You can put a very fine point on where exactly you decide you're at 100% DOD, but in reality, once you hit the knee, you're done. Look at the graph and you can see pretty clearly that lowering the voltage for 100% DOD provides very little gain.

Seeing stuff like that is one of the reasons that, although the data collection process is pretty boring, the results make it worth the effort.

Back in the '80s, I tested Duracells against Energizers as part of my job. We needed reliable batteries for the instruments we made. We found that a "good" Duracell had about 10% higher capacity than a "good" Energizer, but with one big caveat. Roughly one in six Duracells were duds, and only put out about a quarter of the stated capacity. They'd get to a point in the discharge where the impedance would rise rather dramatically, and shortly after the voltage would nosedive.
The reason for the difference was that the Duracells were somehow spiked with a little mercury. It made them a bit hotter, but less reliable. My company disqualified Duracells based on the test results.

Anyway, I don't know if they still do this (or if they would be allowed to). It's just an example of another performance-vs-reliability tradeoff. The LiCoO2-vs-LiFePO4 debate sounds similar.

-Mark


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## _GonZo_ (Mar 23, 2009)

Hi Mark,

Can you post any of the discharging curves so we can have a look at them.

I have been testing battery cells for over 6 year now (mainly Lipo cells) so I think I may give you some clues about.

Let us know as well the sizes and weigth of the cells.


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## Wirecutter (Jul 26, 2007)

Zo -
Check out my above post from 27 Oct. That's got the raw data, and you can plot that out with any spreadsheet program. I'm currently developing data for some 0.5C discharge tests, and I'm going to serialize the packs I have and make a couple more of each with the same make-up.

So far, I've been testing Samsung and Tenergy 18650 cells with LiCoO2 chemistry. (18650 means 18mm diameter and 65.0 mm length - standard laptop battery pack cells.) I don't have the weights handy, but I'll try to run down a spec sheet. I've also got some 4Ah 26650 LiMnNi cells coming, and I'll make and test a couple of packs of those. Mostly I'm just trying to determine if cells perform as they're supposed to. So far, it's been a bit disappointing.

Sounds like there are a few of us running data. Would there be interest in a new area where data can be uploaded/downloaded for easy access?

-M


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## IamIan (Mar 29, 2009)

Wirecutter said:


> I haven't done any calibration, but I'm using pretty short, fat wires and good connectors. I think at the current and voltage levels I'm working at, it's not a significant factor.


Fair and true enough.



Wirecutter said:


> I haven't gotten into charge monitoring yet. Is that in the basic software package, or do I need to upgrade?


I have the upgraded software ... but as I recall even the basic version can do it... you set the discharge current level to 0mA... it will then track & log the voltage of a battery during charging.... If you have the upgraded software you can also log the temperature as well.



Wirecutter said:


> Anyway, for right now, I'm just collecting data and trying to determine which battery makers are the real deal and which are full of spit. I'll make my data available, too.


Enjoy it... I know I have been.

I sometimes run the data logging PC interface from my Multi-meter in conjunction with the CBA-II That way I can monitor and log a variety of different variables all at the same time for the same test.

I kind of ran into a wall with Higher current testing ... and so I have been considering one of the amplifiers... multiple CBA units would be nice... but an amplifier would be higher on my list than multiple units.


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## _GonZo_ (Mar 23, 2009)

Hi Mark,

Sorry I missed that file, now I have checked it.

Any way what I need is to see the discarging curves. (like the attachement)
I need to look at the voltage variations during discharge. 
You can open the curves on the CBA and then capture screen that is enough for me.

As well you can send me the curves on original format by e-mail to:
[email protected]
(But you will have to wait some our for my response there because now I am on a Mac and the CBA program does not run on Aple...)


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## Wirecutter (Jul 26, 2007)

I did an overlay of all the tests so far and emailed it to you.

-M


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## _GonZo_ (Mar 23, 2009)

Hi Mark,

Received your e-mail an checked.
In order to make it more simple to understand I just let 2 diferent discharging curves of the 2 packs on the chart.
One at 0,5C and the other at 1C per each pack.

For the grafic I think you made the discharging curves at a room temperaure around 15ºC and/or room/cell temperature is different from some discharges to others. (for next times better around 20ºC and always the same for all discharges)

Both packs are not high discharge packs so they are made to work around 0.2C to 0,5C maximun eventualy can hold 2C discharges for some seconds.
Make them work over that will kill them in days.

The discharging curve that goes up after a while of the start (blue line) is caused because the cell needs to heat up in order to deliver the recuested power. (unless the initial cell temperature was too low)
That tipe of curves are over the limit of the cell so that cell can not hold a 2.6A discharge, is too much for it.


First the TE2600-4S:
This pack for what I can see in the grafh has a PCM circuit instaled, the PCM is working correctly.
Shuts down the pack when low voltage is detected in any cell.
As well per the starting voltage of the pack it is as well cutting charging when maximun voltage of any cell reachs maximun.
There is a little inbalance between the cells but not much this causes a lost around a 5%.
The PCM causes as well some looses, but not much.
And the bad news: The cells or are used or very old. (capacity is way under 80%)
Or they told you they are 2600mAh capacity but they are only 1900mAh.
I sugest that you send them back to provider.

The Sung2200-4S pack:
It is in better conditions than the other, but still too low capacity for a new pack. Under that discharge rated it should be giving you over 2000mAh.
So same as the other, send back to provider.


For reference this type of packs on a 0.1C at 20ºC discharge should give you at least the nominal capacity, usually more.

Hope it helps.

Any question welcome.


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## Wirecutter (Jul 26, 2007)

I got them about 6 months ago, but I never used them until recently. For right now, I'll cut the vendor a little slack because I didn't put them to use right away. Still, I thought lithiums had a great shelf life. I was also a little surprised because of what others seemed to have experienced. Most of the postings I've read here and elsewhere report that new cells are usually good for slightly higher than stated capacity, at least initially. Stated capacity is supposed to be a _minimum_ number, not a maximum, as I've seen. 

Going forward, when I get ready to purchase cells, I'll do a "test" purchase and run the cells through their paces right away. I got some yesterday and built up a pack, and I'll be testing it tonight.

-M


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## _GonZo_ (Mar 23, 2009)

Wirecutter said:


> I got them about 6 months ago, but I never used them until recently. For right now, I'll cut the vendor a little slack because I didn't put them to use right away. Still, I thought lithiums had a great shelf life. I was also a little surprised because of what others seemed to have experienced. Most of the postings I've read here and elsewhere report that new cells are usually good for slightly higher than stated capacity, at least initially. Stated capacity is supposed to be a _minimum_ number, not a maximum, as I've seen.
> 
> Going forward, when I get ready to purchase cells, I'll do a "test" purchase and run the cells through their paces right away. I got some yesterday and built up a pack, and I'll be testing it tonight.
> 
> -M


Yes shelf life is good over 2 years with no apreciable difference if stored correctly. (halh charge and room temperature 10-30ºC)

After that some capacity can be lost but not so much, unless the quality is very bad.

The nominal capacity stated is a minimun, as you say they usually give a little more when new.


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## czwbattery (Oct 13, 2009)

It is no any usefull. That is , normal testing is with any helpful. 

For cell, we must consider their Inner direct resistance, and their Inner pulse currency, and discharge rate, and voltage, capacities, end of discharge, end of charge, IR , IDR etc.
All the Data s are same, and then pack them into a same group.

And then, testing their discharge ragte, EOD discharge/charge voltage, etc. 

So we can find the test results. And the results are great helpful for you. 

Please have a try.

www.czwbattery.com


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## Wirecutter (Jul 26, 2007)

Czwbattery, I'm not sure I understand all of what you're trying to say, but I will be posting more data. You may just be the manufacturer of some of the cells I'm testing.

The LiMnNi 26650 4000mAh cells mentioned in my post of 4 Nov were built up into a pack of 4 cells in series. I welded tabs on them, and the tabs are either welded to the adjacent cell or are soldered to the protection circuit. The circuit protects against under-charge (V too low), over-charge (V too high), and excessive current _for all cells_. I think it also performs cell balancing, but I need to check that. In all the tests I've run so far, I've only once discharged at 1.5C. All other tests were at 1.0C and below. Most recent tests have below 0.25C. I don't have the data handy, but I'll post it later today.

I *still* have not seen any batteries perform to spec!  More info: Based on information posted by IamIan on 26 Oct, I've modified my testing regime. After every charge or discharge, I let the pack rest for at least 5 hours so it can chemically stabilize. I can't speak for the temperatures the cells experienced before I got them, but since I've had them, they've never been above 30 degrees C or below 19 degrees C. The only variations occur when the batteries are at rest and the programmable thermostat in my house throttles back when I'm away. All charging and testing is done at room temp.

So far, I think I'm doing everything right. I haven't abused the cells, and all the data I've posted has been from new cells. I'm trying lower and lower discharge rates in an attempt to get any pack to provide rated capacity. So far, I'm below 0.25C and haven't seen any pack perform to spec. For liability reasons, all the battery and charger makers insist that the cells never get charged or discharged while unattended. This means I have to "be around" whenever I'm testing, which is kind of a hassle on tests that run 4 or more hours each. I know the setups I'm using _probably_ won't catch fire, but I'm not going to bet the house on it...(pun intended)

After all this effort, am I simply uncovering BS in the battery specs? I hope not. I would love to return the cells that under-perform, but I wonder how the vendor feels about the return of cells that have had tabs and protection circuits welded (not soldered) to them. I'll check into that.

The biggest difference in the cells I'm testing and others I've heard about seems to be the size. Perhaps battery manufacturers are a bit more rigorous with cells costing $hundreds per cell. Is anyone else out there testing smaller cells like 26650s or 18650s?

-M


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## IamIan (Mar 29, 2009)

good stuff... 

A trick I've done for the staying attended part.

I put start a test... then minimize the window while I check email ... this forum ... surf the web ... etc...

But if there are two things I would change about the CBA series it would be:

#1>
Charge testing as well as discharge testing.

#2>
Automated programmable tests.


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## Wirecutter (Jul 26, 2007)

As promised, I've attached the graphs for the 26650 4000mAh cells purchased from Battery Space dot com. The pack is 4 cells in series. The protection circuit allows max charging voltage of 4.2v/cell and a max discharge voltage of 2.4v/cell. (My tests end at 2.8v/cell) The circuit also features cell balancing and a max discharge current of 10A. I've submitted and RMA request for the remainder of the order that I got these cells on.

If anyone wants it, I can also provide the raw data.

-Mark


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## _GonZo_ (Mar 23, 2009)

Wirecutter said:


> As promised, I've attached the graphs for the 26650 4000mAh cells purchased from Battery Space dot com. The pack is 4 cells in series. The protection circuit allows max charging voltage of 4.2v/cell and a max discharge voltage of 2.4v/cell. (My tests end at 2.8v/cell) The circuit also features cell balancing and a max discharge current of 10A. I've submitted and RMA request for the remainder of the order that I got these cells on.
> 
> If anyone wants it, I can also provide the raw data.
> 
> -Mark


Can you tell us what is the final voltage of the pack/s just when it finish charge or if posible of each cell.


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