Hey people,
Wonder if you could help me figure out the capacity of each 18650 cell?
I’m trying to re-purpose the cells so i can power up a few motion sensor LEDs in the house, the trouble is that these cells have zero labels or printing on them
What I can tell you is I have 6 cells that have been salvaged from a laptop battery. The label on the battery pack states the following, 10.8v 51Wh and 10.8v 4440mAh. I managed to carefully split open the battery pack and the battery pack is still in tact, until I can figure out each cell’s capacity. It looks like there are 3 pairs of cells. More than happy to share a photo or basic diagram if it helps, hopefully the above info will be of some help.
Thanks guys
They were probably 2220mAh cells originally, but if they’ve been used heavily in a laptop they might have less capacity now.
They will have been wired up in parallel in pairs, then three of these pairs in series (known as 3S2P). 10.8/3 = 3.6V, which is the nominal voltage of some of these cells
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Thanks
Yes, they have been used but going by the usage of the laptop, it was hardly ever discharged as the laptop was plugged into the charger 90% of it’s lifespan.
At 1st I thought each cell was around 1480mAh, I used the basic calculation of 4440mAh total capacity (as stated on the battery pack) divided by 3 (3 pairs of cells)
Thanks again for your reply
How will you charge them?
Many hobby chargers have a capacity test function.
Cheers
I currently have 2 options, the cheaper TP4056 si gle cell charger and the iMax B6 multi cell charger.
Would you have any advice of how i know what the capacity of eqch cell would be?
Maybe buy a charger that has a capacity test feature? If you are going to be using liIon cells such a device is almost a necessity.
The IMAX (with suitable cell holder) will both charge and do a capacity discharge. I have a similar unit.
In a way it doesn’t matter WHAT they are/were since they are worn now. They will be what they will be.
FWIW one of the funky things you can do to a lithium battery (pack) is what happened to that one…keep charged full all the time. Unfortunately laptop packs generally have a hard life.
If there are any marks at all you might be able to use one of these for an ID:
18650 Lithium Ion Battery Identification Reference
Mandrake has a point. If you are going to get involved with this you may want a (capacity) charger that is more user friendly.
If you don’t have any equipment with the ability to measure something (volts, current, resistance, or capacity) there is no way to know the actual capacity of the 6 cells you have. A charger with that function can be handy (if you can trust it).
Merlot is spot on with the original capacity of the cells was 2200mAHr each. I have many laptop cells (over 50) and my experience is the capacity generally does not degrade all that much. I have 4 sets that I characterized, and 3 of them were down 5-10% of the original rating, one set was down 10-15%. Some were extremely discharged when I opened the pack, and still measured capacity in the range stated above.
Is this the sort of answer you’re looking for?
Hi and thanks for reply. I’ll research into the merlot device you mentioned.
In terms of your response, yes and no to be honest. I thought there was a mathematical way to calculate the capacity of each cell by the overall rating on the battery pack vs the number of cells and their original packaging, ie 3s2p for example…
Thanks again
There is, and merlot alluded to it above, in detail this is how you would calculate the original capacity. So the pack was constructed by taking three sets of cells and connecting them in series, each set consisted of two cells in parallel, for a total of six cells all together. Is that what your pack looked like when it was taken apart? Note each round 18650 is properly identified as a cell, not a battery. The words are often used (improperly) interchangeably as even the manufacturers market batteries, not cells. When you take cells and connect them in series or parallel (or both) you create a battery.
Individual cells capacity for laptop 18650 cells is based on a certain voltage, generally 3.6 or 3.7 volts. The 3s is three cells in series. So three times 3.6 is 10.8 volts. That is what the pack labeled if I remember correctly. 2p is two cells in parallel. Because the total capacity of the battery was rated at 4400 milliamperes-hours, Each cell was rated at 2200 milliamperes-hours. The capacity of the cells as you put the cells in parallel, and the voltage of the pack adds as you put the blocks in series.
So you should have 6 cells that were originally rated at 2200 milliamperes-hours of capacity.
As I read what I wrote above it looks sort of clumsy, but I hope that it helps.
Edit for poor voice to text
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Hi and thanks for your detailed and well-explained response.
Correct, the battery pack consists of 6 cells in total
This would indicate 3s2p configuration, i think…
yes, that is correct
Yes the 3 s is three in series. at 3.6 volts rated that gives you the 3X3.6= 10.8 volts which is the rating of the pack. The pack is rated at 4400 mAh with 2 in parallel (2P) we would divide by 2 to get the single cell capacity . 4400/2 =2200 mAh per cell. Just remember when you put cells in series, you add the voltages. When you put them in parallel, you add the capacities.
All this was said before, but I thought I would try to clarify for you.
Makes perfect sense - thank you to every single reply, much appreciated 
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