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.
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.
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.
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.
Specifically the pack I opened was for the T400.
The part number for that is: 43R2499
It was a 9 cell battery.
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.
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.
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.
I used your way to figure out the same answer:
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.
So buy Cells made in Korea for LG and chance every other sell if they are from china?
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. 
Thank you everyone for your replies.
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.
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.)
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.
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.
If you really want to dive into the deep end of the pool, you could start here: How to calculate battery run-time
Dim
+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.
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.
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!
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.
48WH/11.1V=4.32AH
4.32AH/2=2.16AH
implies 2200mAH cells
and it's 3S2P.
Apparently my Low-Alcohol Warning Alarm isn’t working.
Thanks for the correction.