How is it possible a dead old Lithium battery becomes charged after opened?
It's not magic, there is a dual layer capacitance ( weak memory ) but main capacitance from aging may have reduced from  10kF to &lt;&lt; 10% with ESR > 100x norm.

Considering 18650 normal energy storage up to 10 Joules full, you have &lt;=1% of this energy in storage, is my guestimate.  

Remember Voltage is just potential, and Resistance is futile if its too high... ;)

Do a 10K R load test and measure dV/dt=Ic/C  from 4 to 3.6V
If you can then do 100R load test from similar conditions down to say 3.1V    

Record the results with drop and changes then compute C again. This difference can be modelled crudely by R1+C1//R2+C2 

Then present your model to us, if you can.







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