Drone lipo battery not working properly
The most common symptoms of a "dead" battery, such as an 18650 cell are that the effective capacitance reduces from 10k Farads to &lt; 1% so that it overcharges without a balancer and quickly undercharges and even reverse charges under load unless protected such as with a balancer which is now powered by the batteries.

The other characteristic is the ESR rises from 50 mOhm to >100x this value so the lower resistance of the balancer allows loop current to flow.

However passive balancers only have enough 5~10% imbalance [W] capacity to bypass the reduced current level  that occurs after CC mode to CV mode where the mobile cuts out charge usually around 5% to 10% of the CC level. 

This gives rise to the 3rd common characteristics of all dead battery packs.  Each high quality pack will have cells that are imbalanced  &lt;&lt; 1% and preferably &lt; 0.1% while a dead pack will have at least  one in the array that is worse than 10% lower capacity or lower resting voltage after full charge  than the rest.  Once this happens it is like thermal runaway or positive feedback because imbalance causes more imbalance and reaches low voltage 1st, which accelerates aging on the imbalanced cell so it quickly ages faster than the rest of the cells. This is why battery balancers extend the useful life of packs.  However, 2V Cell balancers are not used in car Lead acid batteries because they all share the same electrolyte and plates are inherently better matched &lt;0.1%. They are more tolerant with H2 outgassing but will eventually have one completely dead cell or major imbalanced when defective.