I accidentally shorted three 18650, 3700 mAh batteries connected in series for about 2 seconds. I measured each cell individually with a voltmeter and they read very close to its original rated voltage of 3.7 V. However, when I tried to use the batteries to drive a DC motor, it doesn't work. How do I tell if the 18650 batteries are dead? If the voltage between each cell is close to 3.7, can I say that it is still well and alive?

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    \$\begingroup\$ 18650s that say 3700mAh are very likely much smaller capacity. A 2 second short is not likely to have destroyed them although it is likely more than their rated current flowed, aging them somewhat. Did the batteries work to drive the motor before? Do they have short circuit protection? Are you sure the polarity is correct if the motor is unidirectional? \$\endgroup\$ – K H Apr 6 at 7:19
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    \$\begingroup\$ Most probably fine. You need to measure IR, capacity and leakage to tell for sure. \$\endgroup\$ – winny Apr 6 at 7:22
  • \$\begingroup\$ I did the same with 20 Amp drain one for about 6 second. They become warm maybe 70degC, the wire also. I didnt notice almost any change in voltage, still about 4V, works fine. Did you measure the voltage under motor loading? \$\endgroup\$ – Michal Podmanický Apr 6 at 7:40
  • \$\begingroup\$ @KH Yes before the short, the motors were driven. Not sure if they have short circuit protection. Also, forgot to mention that some smoke were present at the wire area i believe. This is probably due to the heat produced at the tip of the wires instead of the battery component burning right? If i charge the battery, it should work fine I believe? \$\endgroup\$ – Ong Chee Wei Apr 6 at 7:50
  • \$\begingroup\$ Have you charged the batteries since shorting them? \$\endgroup\$ – K H Apr 6 at 7:52

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