Cell voltages drop after the charge completes. This is often the normal behavior of the cell. A cell’s voltage will rise when it is being charged and will begin to drop somewhat after the charge current has been removed. This is a result of many factors, but primarily due to internal resistance of the cell and the charge characteristics of the chemistry. The amount of voltage drop after the charge stops varies based on the exact chemistry of the cell, the charge “C” rate (charge amperage), and other factors such as the age of the cell, temperature, etc. Iron-phosphate chemistries in particular are known for dropping from 3.6V to about 3.35V after the charge has stopped. Other chemistries may drop less such as from 4.2V to 4.1V. This is normal battery behavior and does not necessarily indicate that the cell is being discharged or that there is missing capacity.
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