# Individual 18650 capacity formula? | Best brand laptop battery for 18650 cells?

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CircaM
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Individual 18650 capacity formula? | Best brand laptop battery for 18650 cells?

I was going to order some 18650s for my light from FastTech(I still might) but they sent me a message saying batteries can't be sent out due to the shipping problems.

So I am going to buy a laptop battery pack and take it appart for the 18650s.

Does anyone have any experience with getting good brand name (Panasonic NCR18650, LG, etc) 18650s from any specific battery pack model or manufacturer?

And how would I calculate the individual cell mAh if I have the Voltage, Number of Cells, and pack mAh/Ah?

Thank you.

UPDATE!

For convenience I am adding the formula to calculate capacity here.

Here is my formula:

[(Total Pack Capacity (mAh) * # of cells in pack) / # of parallels] / total # of cells = mAh per 18650 cell.

So 4800mAh pack, of 9 cell, 3 parallels.

[(4800*9)/3]/9=1600mAh per cell.

(Note: that is a brand new never used battery pack)

* = multiply; / = divide. Follow order of operations!

Good Luck!

Edited by: CircaM on 11/27/2013 - 17:37
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CircaM wrote:
So I am going to buy a laptop battery pack and take it appart for the 18650s.
Welcome to the club!

The only advice I’d offer is, before you risk your hard-earned money buying one, go out into your local world & find a computer repair store — preferably a small “mom-&-pop” store — for some “practice dummies”, i.e. “dead” packs. Ask to speak with the owner or service manager on duty. Explain to them how you’re trying to recycle “dead” laptop batteries for the cells inside. Take a flashlight to show off if you want to. Even explain that normally the cells are fine, the pack has died because the protection circuit has failed. Or don’t but it helps to make sure they understand you will diligently follow all laws and codes and will recycle each tiny piece with gusto.

Normally, they’ll likely have a box half-full of them. If they let you pick, start with the cleanest, newest one (likely less abused) and take as many as they will let you.

Computer service managers are an intelligent, curious, friendly bunch and mostly bored on the job, so the off-the-wall visit and some relevant-but-largely-useless information might be appreciated. But they do have bosses so be sensitive to their time. Speaking of time, it would be best to go by when their parking lot is empty…

If you like Engineering, you can practice it here by profiling the pack manufacturers vs. the cells inside, vs. those cells’ performance. Now you will have the answer to your question.

No cost but gas money. And the chance to make a friend.

Quote:
Does anyone have any experience with getting good brand name (Panasonic NCR18650, LG, etc) 18650s from any specific battery pack model or manufacturer?
Yes.

The important fact to remember is, the bigger the buyer the better the buy. Look to the top laptop sales leaders & try those. I see you’re looking to find which pack might contain what cells, so I apologize for not having a clue about that. Years ago, “the trades” were pulp magazines that published stuff like production numbers and who’s doing what with whom, but I’m sure there’s a WWWeb site for that now.

Packs for older models tend to have lower-capacity, older cells; newer packs, vice-versa, obviously.

Perhaps you could start by deciding how much you’re willing to spend on a new pack & then finding the newest Dell, Alienware or HP laptop whose battery costs ‘that’ much. Whatever cells you get will make you happy.

Quote:
And how would I calculate the individual cell mAh if I have the Voltage, Number of Cells, and pack mAh/Ah?
That’s an obvious algebra equation, IFF you know the Parallel/Series relationship of the cells, and the number thereof, in the individual pack in question. Parallel multiplies V, Series multiplies mAh.

There’s an easier way. The individual cells are marked with codes, which you can Google or bring here. That will give you the same Capacity number, easier.

Or perhaps you’re trying to pick which pack you buy based on its mAh rating. I’d bet the farm that the deepest number on all packs of x Volts would have the deepest cells inside. As long as you don’t expect to actually see that mAh from any of them, that should get you the deepest available.

I’d really like to see you take a pack — bought new or not, and profile all the cells in it; to see how closely they are to A: each other and B: the published spec for that cell. I’m going to wager you don’t see any two the same.

As for me, I’m not picky over fist-fulls of free batteries, but my work puts more Dell packs in my hands than any other. The newer Dells have some nice 18650s in them (e.g. ) LGABC11865 (“2800 mAh”) and SE US18650GR.

_
Dim

“There is no darkness but ignorance.”

LazyJ
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All the Sonys and Lenovos I’ve tore into had Panasonics. I’ve had great luck with Dell also, Sanyos, sometimes LG. We have HP laptops at work, the six cell packs last six months at most, and I’ve cracked open dozens of them, the same Sanyos that Dell uses, but they’ve all been toasted.

CircaM
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Thank you both for the replies. I'm going to try to grab a Used/Working Dell (Or lenovo or sony)pack for about \$1 a cell.

Since a higher voltage pack will likely yield better batteries, does a higher W/h pack mean higher capacity cells?

I can get Wh/mAh(of pack), Voltage, # of cells, number of paraelles(guessed), etc.

Example battery: 48Wh, 11.1v, 6 cell, 2 paraelles of 3 cells.

Could anyone give me an example or, better yet, a formula for calculating individual cell capacity?

gregs656
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I think I am going to have to try this.

I guess you need a charger that is good enough to test the condition of the batteries? Or is it a case of charging anything showing a decent voltage and letting them self discharge over a set period of time, then retesting the voltage?

This whole idea just makes complete sense to me, a great way to recycle.

CircaM
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gregs656 wrote:
I think I am going to have to try this. I guess you need a charger that is good enough to test the condition of the batteries? Or is it a case of charging anything showing a decent voltage and letting them self discharge over a set period of time, then retesting the voltage? This whole idea just makes complete sense to me, a great way to recycle.

Check out post#4. It is supposedly how to test a battery to see if it's worth keeping.

Looks like it's only using a Digital MultiMeter to test voltage.

gregs656
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Thanks for that.

A good harvest from one battery pack would do me for quite a while, esp as a couple of my lights have low voltage indication.

CircaM
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Still trying to find a formula to calculate individual cell capacity of the 18650s in a laptop battery pack.

Here is my guess for a formula:

[(Total Pack Capacity (mAh) * # of cells in pack) / # of parallels] / total # of cells = mAh per 18650 cell.

So 4800mAh pack, of 9 cell, 3 parallels.

[(4800*9)/3]/9=1600mAh per cell.

(Note: that is a brand new never used battery pack)

Can anyone test that formula? I don't have a capacity meter.

FMcamaroZ28
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I like going for recent Lenovo cells. (used to be IBM)

They have only been marked Lenovo only for about 5 years, and all 5 of the packs i’ve opened had Sanyo 2600UR cells.

CircaM
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FMcamaroZ28 wrote:
I like going for recent Lenovo cells. (used to be IBM) They have only been marked Lenovo only for about 5 years, and all 5 of the packs i've opened had Sanyo 2600UR cells.

Can you post or PM me a model number for the battery pack itsself?

I want to test my formula to see if it's close.

Also, I think I'm going to go for lenovo or sonys aswell, seem to be alot of them cheaper than dells.

FMcamaroZ28
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Specifically the pack I opened was for the T400.

The part number for that is: 43R2499

It was a 9 cell battery.

BIGWOOD
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Sometimes you get lucky and the sticker on the battery pack will tell you what brand of batteries it has inside.

Here are the tell-tale signs.

Zoom in on the picture to see what I’m talking about.

http://www.summit4laptops.com/files/items/HP%20Laptop%20Battery%206120-20120807-160629.jpg

Where is it made?  CELL ORIGIN KOREA FURTHER PROCESSED IN CHINA

Battery is from Korea.  Hmm… the only lithium battery I know to come out of Korea is LG.

There’s also a code which I’m guessing is the code for the battery. “SDI-CHA-LG

Opened it up…Yup, it has LG cells inside.

comfychair
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Search ebay for 'HP 9600mAh', you'll find new aftermarket replacement packs with 12 2400mAh no-name but solid cells inside, for around \$30. They're not spectacular, but they are all new, and you won't have to throw half of them away like you will with a clapped-out abused used pack.

We've found Toshiba 6-cell packs with grey Panasonic 2900s, and Acer packs with the nice purple 4.30v 2800mAh Samsung ICR 28As inside. New or new old stock packs are almost always better value for money, breaking open used packs really only makes sense if they're free or nearly free. Don't spend real money on used packs, you might get a few good ones but you'll also end up with a lot of stuff that has to go in the recycle bin.

CircaM
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FMcamaroZ28 wrote:
Specifically the pack I opened was for the T400. The part number for that is: 43R2499 It was a 9 cell battery.

Just used my formula on that pack
Capacity: 7.8Ah / 7800mAh
Cell: 9 Cells
Paraelle: 3 rows of 3(Guessing)

[(7800*9)/3]/9=2600mAh per cell.

gauss163 wrote:
Here's one way to compute cell capacity from pack ratings. Let's take your example of a 6 cell pack rated 11.1V, 48Wh. Now 48/11.1 = 4.324Ah = 4324mAh. And 11.1V/3.7V = 3, so the pack has 3 cells in series, so 6/3 = 2 cells in parallel; thus 4324/2 = 2162mAh/cell. So they're probably 2150 mAh cells, indeed 11.1 * 2.15 * 2 = 47.73Wh, which rounds to 48 Wh, as rated.

48Wh/10.8V=7.778Ah=7778mAh
10.8V/3.7V=2.92 so round up to 3 paraelle.
9/3=3
So, 7778/3=2592. Up to 2600mAh per cell.

BIGWOOD wrote:

Where is it made?  CELL ORIGIN KOREA FURTHER PROCESSED IN CHINA

Battery is from Korea.  Hmm… the only lithium battery I know to come out of Korea is LG.

There’s also a code which I’m guessing is the code for the battery. “SDI-CHA-LG

Opened it up…Yup, it has LG cells inside.

So buy Cells made in Korea for LG and chance every other sell if they are from china?

BIGWOOD
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I guess what I'm trying to say is that sometimes you'll get lucky and the label on the battery will tell you if it's an LG, Samsung, or Sony battery inside.

CircaM
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Thank you everyone for your replies.

gauss163 wrote:
Or, if you were doing the calculation for the 7.8Ah 9-cell 3s3p pack then its 7.8/3 = 2.6Ah/cell.

Yeah, on that one I was doing it for FMcamaroZ28's pack, since we knew what the final value of each cell should have been.
Just wanted to see if my math worked correctly for each cell.
Thank you for the help calculating gauss.

BIGWOOD wrote:
I guess what I'm trying to say is that sometimes you'll get lucky and the label on the battery will tell you if it's an LG, Samsung, or Sony battery inside.

I knew what you meant, I will definitely look for markings like that. Thanks for that tip.

Would a higher capacity battery, like an 85Wh, or 5200mAh mean higher capacity 18650s inside? (I even saw one that was like 104Wh.)

Gj
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Probably, but not necessarily. It depends how many cells there are. I've only seen one 14.4V battery (4s), all the rest say 10.8 or 11.1V, which is 3s. Take the number of cells/3, or 4 for a 14.4V pack, and that's the 'p' number, the number of cells in parallel. divide the mAH rating of the battery by the 'p' number to get the individual cell's mAH rating.

8steve88
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I’m using two of these in my two laptops. I usually run them plugged into the mains and charging they are about 4 years old now. Do you think that they’d be worth stripping down when they eventually fail? I’ve still got the two original 6 cell packs with only about 3 weeks use on them then charged and stored, any good do you reckon. The new packs are £57 ~ \$90 so I’m going to use these until they fail.
I’d like to think that I have a few cells for any emergency situation that might occur.

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CircaM wrote:
Example battery: 48Wh, 11.1v
If you really want to dive into the deep end of the pool, you could start here: How to calculate battery run-time

Dim

“There is no darkness but ignorance.”

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comfychair wrote:
breaking open used packs really only makes sense if they’re free or nearly free. Don’t spend real money on used packs
+1

Only gas money.

If someone tries to sell you a dead battery pack, feel free to, as the saying goes “use whatever language you deem appropriate” and stop going there.

“There is no darkness but ignorance.”

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8steve88 wrote:
I usually run them plugged into the mains and charging they are about 4 years old now.
OT, with apologies.

I believe, and cannot prove, that what you are doing will extend the life of your packs and cells.

I have an Inspiron with 2 packs, and I always left one in the bag, one in the PC on the wire. I’d swap them when onsite and one ran down. I considered one as a “favorite”, but tried to keep them both topped off. I didn’t think about it until it was too late, but one of them died a lot sooner than the other.

If you could stand to kill one, maybe you could pick one to stay on the wire and the other to get deeply discharged and recharged as needed… That might answer some of the “dead pack” questions…

Just sayin…

PS: the individual cells should be in the 2200mAh range, which means they’re not all that exciting, but they’d certainly make lots of light for you.

“There is no darkness but ignorance.”

gregs656
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Was in town earlier and stopped in at a PC repair place, he is going to see if he has any dead laptop batteries – but they might have just been chucked out. Going back tomorrow.

Got two chances I guess!

Bergtjie
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comfychair wrote:
New or new old stock packs are almost always better value for money, breaking open used packs really only makes sense if they’re free or nearly free. Don’t spend real money on used packs, you might get a few good ones but you’ll also end up with a lot of stuff that has to go in the recycle bin.

Got lucky today, clients laptop was stolen and he had a habit if using his laptop without battery installed, I ended up with 6 Sanyo cells that are 4V pulled , busy charging now before I do capacity tests.

Gj
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So if I can still do math, 11.1vDC/3.7 = 3P, 2S. 48Wh/2S = 24Wh = 2400mWh/3.7 = 648.7 mAh. That seems strange. Are you sure it's not 48Ah? Be sure you examine a photograph of the battery's label, and never trust the ad copy. I could be dead wrong on the math, but 2400mAh seems a lot more likely.

48WH/11.1V=4.32AH

4.32AH/2=2.16AH

implies 2200mAH cells

and it's 3S2P.

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Apparently my Low-Alcohol Warning Alarm isn’t working.

Thanks for the correction.

“There is no darkness but ignorance.”

Gj
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Right, I haven't seen 2150's yet so went with the closest size I've come across.

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gauss163 wrote:
It appears that your slips were not in arithmetic but in how to calculate
Believe it or not, I re-wrote that part something like seven or eight times, trying to come up with some unifying formula. I kept stumbling over second-order unknowns like the current draw and residual capacity at the low-voltage cutoff (and that nagging low-alcohol warning) … But that kept me from seeing all the other, more sensible posts.

Plus, it turns out, it’s hard to find a pack rated in “Wh”. The ads may say that, but the labels on the packs mostly seem to give V and mAh, which is much easier to compute. But why would any of that matter since I know I’ll get a different runtime out of my “xyz” cell than you will of yours, even from the same batch, just because we use them differently.

Then the magic mushrooms wore off and it dawned on me, the OP is probably just looking to buy a pack to rob, with the deepest cells in it, & needs a way to tell which is which. That’s the only thing that makes sense, with the “YMMV” rule in effect.

So, just to kick me and my dog :bigsmile: (just kidding), would you concur that, given the different rated pack voltages, wouldn’t the “plain” Wh ratings (or calculation) of packs serve to show which has the deepest cells?

I’m not sure it matters at all to me. As long as laptop packs die, I will continue to churn these freebies “with extreme prejudice”. But if a fellow had to buy the best pack available as a cell donor, it would be handy to have a way to pick the best.

Dim

“There is no darkness but ignorance.”

gregs656
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Went back to the computer repair place today, didn’t exactly hit a gold mine but I did walk away with 1 6 cell Dell battery. A bit of butchery later, and I got 4 cells reading 4v, 1 reading 1v and 1 reading 0v.

They are grey LG cells.

I asked the owner to hold on to any laptop batteries he gets in, he didn’t seem to think they got many in but agreed all the same.

Beginners luck?

dchomak
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I was at the Lowes return desk today to return a lamp. That area is were the recycle bin is. I reached in and pulled out this. I only took the one, what am I a pig?
Anyway here are the pics, no words are necessary. I am charging them up as I post this.

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You need a bigger hammer!

Edit: “Fukushima”??? Them is NUKULAR Batteries!

(Seriously, nice find! Those US18650GR’s have been reviewed here. I have a batch & love ‘em.)

“There is no darkness but ignorance.”

CircaM
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No pain, no gain, dchomak?
Don't worry... with bleeding... the blood will always stop... one way or the other.

Hope you didn't get hurt to badly.

Anyways: For your cells: 4400mAh, 6 cell, 2 parallels.
[(4,400mAh x 6cells) ÷ 2 parallels] ÷ 6cells = 2200mAh min capacity per cell (Actual min capacity 2291mAh per US18650GT's thread)

I got a New Dell cell origin Korea (Only korea cell: LG) Extended battery coming. Thinking it will yield 3000mAh Pink LGs. Will post once it arrives.

Does anyone have any info on which brands will come from a cell origin? Like LGs from Korea.

What comes from Japan?