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I like electronics but I basically don't know anything about it (electricity is too complex), the thing is that I've opened a battery from an old laptop that reads "10.8 V 4300 mAh Li-ion"

The battery-pack contains other 6 batteries and a circuit inside, I suppose that the circuit is just for showing battery info in the computer, charge indicator and for preventing 'overcharge'. Batteries shows 2x 0.0 V, 2x 3.11 V and 2x 3.17 V (with a tester), but that's just their current charge, there's no info on them more than a serial number so...

There's a way to SAFELY recharge them? I'm not in a hurry so time is not a problem.

I thought about put them 0.5 V higher than they currently have over and over until they don't get any higher voltage, but I'm not sure if that will work nor if that will even recharge them.

PS: I thought that Li-Ion batteries didn't contain a pack of standard batteries inside...

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    \$\begingroup\$ general rule of batteries, esp high capacity exotic material batteries... don't mess with them if you don't 100% understand them.... \$\endgroup\$
    – Trevor_G
    Jul 17, 2017 at 15:23
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    \$\begingroup\$ Any Li-ion battery that reads 0.0V is dead. It's unlikely you'll ever charge it properly. \$\endgroup\$
    – Simon B
    Jul 17, 2017 at 15:24
  • \$\begingroup\$ What do you want from that old battery? Do you want it to function in that old laptop, or do you want to re-use the battery cells for some DIY project? \$\endgroup\$ Jul 17, 2017 at 15:25
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    \$\begingroup\$ If you want to take out the 4 good cells, you can. Use a proper Li-ion charger on them. If over-charged or wrongly charged, Li-ion cells have a nasty habit of catching fire. \$\endgroup\$
    – Simon B
    Jul 17, 2017 at 15:34
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    \$\begingroup\$ I doubt that it is the circuit. It is probably one or more cells in the pack that are bad. Time to say goodbye to the battery pack in my opinion. As Simon said, you can take apart the pack if you want, but be careful not to short anything. You might get big sparks. I mean really big sparks, like a welder or something. That eat away small pieces of metal. \$\endgroup\$
    – user57037
    Jul 17, 2017 at 15:36

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If you know nothing about them then be aware that some batteries are not designed to be recharged and can explode if charging is attempted.

For rechargable batteries there is a different charging scheme for each technology. Do it wrong and the battery is likely to explode or catch fire.

I strongly urge that, since by your own assertion that you know nothing about these batteries, STOP experimenting around before you end up hurting yourself, others or destroying property.

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  • \$\begingroup\$ It's a battery pack from a laptop, it's obviously designed for being recharged. I forgot to add the word "SAFELY" to main question, But hey! 'small' batteries can really explode that bad? \$\endgroup\$ Jul 17, 2017 at 15:33
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    \$\begingroup\$ @SopzeLS - Yes they can if they are mishandled. I can assure you that careless experimentation without knowing what you are doing could lead to serious consequences. \$\endgroup\$ Jul 17, 2017 at 15:36
  • \$\begingroup\$ @SopzeLS Here's my favorite answer to that question. \$\endgroup\$
    – Cort Ammon
    Jul 17, 2017 at 17:45
  • \$\begingroup\$ @CortAmmon Ok, I won't recharge my batteries with a knife never again. \$\endgroup\$ Jul 18, 2017 at 17:49
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You have a standard 2P (two parallel) and 3S (3 in series) laptop battery. And yes, all laptop batteries are made of standard cells, from variants of 18650 or 17650 cells. Or flat proprietary cells.

As Simon noted, you have one dead section. While the chances to recover full functionality are small, you can try.

You need to try to "pre-charge" the dead section, which can be done with a small, ~200 mA current applied to this section alone. You don't need to desolder anything, just find a way to connect external leads temporary. The best would be a benchtop power supply, set it to 4.2 V and 200mA current limit. Alternatively you can try a USB charger with a 22 - 33 Ohms resistor in series. After one-two minutes check if the cell builds any voltage. If the voltage goes above 2.5-3 V, you can stop the pre-charging and try to charge the whole battery inside your laptop, using the laptop's AC-DC adapter. I had some successful recoveries using this method.

ADDITION: for those who spread myths about explosiveness of over-discharged batteries. Here is a scholar research on the subject, "Effects of overdischarge on performance and thermal stability of a Li-ion cell" No explosive effects or thermal run-away instabilities were found, other than a loss of capacity (sometimes drastic).

NOTE OF CAUTION: The cells inside laptop batteries don't have built-in protection as many stand-alone cell have nowadays. Be careful not to short them with thick wires. Although no Li-Ion cell explode, they can rapidly "vent", which is sometimes accompanied by flames.

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  • \$\begingroup\$ I agree. I think a lot of the problems come from RC battery packs. The RC guys often charge and discharge the packs VERY fast, and they are subject to mechanical vibration, etc. Occasionally they vent or vent and catch fire. But an 18650 may be able to supply over 100 Amps of short circuit current. That is good for a nice spark for sure. \$\endgroup\$
    – user57037
    Jul 18, 2017 at 4:18
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It is not safe to charge them anymore.

If Lithium batteries drop below a certain voltage, it is dangerous to recharge them. That small board that you have seen has many utilities. It cuts the current to ensure that you never discharge your battery more than this level plus a security margin. It also prevents you to charge it again in case it has discharged naturally below that level, and it also prevents you to charge it over its limit.

If one of your batteries shows 0V it means that it has gone below the non-return level, so don't play with it (unless you want to make it explode).

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