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I disassembled a dead laptop battery and found 6 AA size batteries interconnected. 5 of them still give 1.2V on meter.

If I replace the defective one would the pack be usable again and would it keep charge?enter image description here

Saad
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    I'm pretty sure these are *not* AA-sized. The printing on one of them even specifies they're 18650. – Marcus Müller Mar 11 '18 at 13:24
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    Questions on the repair of consumer electronics, appliances, or other devices must involve specific troubleshooting steps and demonstrate a good understanding of the underlying design of the device being repaired. – Marcus Müller Mar 11 '18 at 13:24

2 Answers2

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I am answering here because others might look up the subject.

Mixing old and new batteries is false economy. You are likely to find one of the remaining 5 batteries to fail soon.

The phrase "throwing good money after bad" is very much applicable here.

Neil_UK
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Oldfart
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They're not AAs, they're 18650 Lithium-Ion batteries, nominal voltage 3.6V.

At 1.2V your batteries have been over-discharged, they're finished. If you recharge them they won't last.

You can replace all cells with quality 18650 LiIons which aren't that expensive ($6-8 a piece). Purchase from a reputable source (ie, not cheap knockoffs from ebay).

bobflux
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    that, by the way, would amount to 36-48$ for battery replacement. Coincidentally relatively close to the price of aftermarket batteries... – Marcus Müller Mar 11 '18 at 13:51
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    And, having replaced the cells, you will probably fail to convince the battery controller on that PCB it's good to go again. (Don't ask me how I know...) –  Mar 11 '18 at 13:59
  • @BrianDrummond That's interesting, well in this case better buy an aftermarket battery... – bobflux Mar 11 '18 at 14:16
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    This is a 2P-3S battery, with two cells in parallel, three in series. When in parallel, each cell in a pair must be closely matched in terms of internal resistance and overall discharge curve (SOH-state of health), otherwise the mismatched pair will wear off rapidly, resulting in the same dead state. So you would need to buy many more batteries than just two. – Ale..chenski Mar 11 '18 at 17:51
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    My issue is Airflight companies don’t accept Laptop batteries on board. Can’t order them, I am in Mauritius and trying to find a solution. I have three laptops working permanently on AC adapter. – Louis Alain Desire Bastien Mar 12 '18 at 14:51
  • [This video](https://www.youtube.com/watch?v=sRwoYJyjZNo&pp=ygUobGl0aGl1bSBiYXR0ZXJ5IGRlZXAgZGlzY2hhcmdlIGRhbmdlcm91cw%3D%3D) and all comments beneath it seems to suggest the following statement is wrong: "At 1.2V your batteries have been over-discharged, they're finished." @bobflux, can you please clarify? – Martin Andersson Aug 12 '23 at 16:27