I have salvaged a lithium-ion battery pack from a laptop.On the case,it is written each battery has 3.7v(they are 18650s),but when I measured using my multimeter I found each battery to be just 2.8v(some were 3.1v and 3.0v). My question is,that is it safe to charge these batteries using normal lithium ion battery chargers(TP4056)? Any answer will be of nice help!
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\$\begingroup\$ Charge how? One by one? Many in paralell/series? \$\endgroup\$– winnyJun 16, 2017 at 8:01
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\$\begingroup\$ @winny Sir,One by one \$\endgroup\$– user150093Jun 16, 2017 at 8:47
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\$\begingroup\$ Then no problem. \$\endgroup\$– winnyJun 16, 2017 at 9:14
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\$\begingroup\$ @winny Hmm,I thought they would blast.Thank you,now I can carry on. \$\endgroup\$– user150093Jun 16, 2017 at 9:27
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3.7 V is purely the nominal voltage. The working voltage is typically around 3.2 to 4.2 V. 2.8 V is lower than you would like but not throw the cell away low.
They should be trickle charged until the voltage recovers back to the normal range but after that they should be fine. Which a decent charger should do automatically.
Obviously all the the normal caveats about begin careful with unprotected Li-ion cells and charging / discharging them using the correct limits and protections still apply.
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\$\begingroup\$ At 2.8V they might not even need to be trickle charged. It may be a good idea, as the specific chemistry is unknown, however above 2.5-2.7 is well within the operating range of most Li-ion. \$\endgroup\$– RedjaJun 16, 2017 at 21:19