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I disassembled an old laptop battery and found 6 Sanyo K29B 18650s.

All of them have a voltage of <= 2.5V.

When I tried to charge them with a TP4056 module, while measuring the current, the module provided 500-700 mA and got the battery to 3V in under 15 seconds.

Are these batteries still good to use?

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1 Answer 1

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Charge them up fully to 4.1v or 4.2v and see if they hold the voltage. Or you could put them in a charge cycle if you have a charger that'll do that (quality RC car chargers work quite excellent for this) for a few rotations and see how they handle that. if there is no issues with the power cycling then I'd say they are just fine. I've taken some 18650's down to 1.5v (accidently, but also kinda on purpose) but running through a few power cycles they work fine and never had an issue with them.

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  • \$\begingroup\$ Thanks for your answer. I had also salvaged 6 other 18650s from a newer laptop battery. The voltages were 2.5 - 3.5. Charged them up to 4.01 - 4.08 (that's what the module allowed me to, maybe they just dropped to this voltage). And luckily i see that after a week, the voltage has dropped maybe for 0.03 at most. \$\endgroup\$
    – jverbys
    Mar 26, 2021 at 22:28

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