Hi....Assuming after use, one cell is routinely 2.8 and the other 3.6, the battery is harmed and should be supplanted. Cells ought to never be released beneath 3.0v, ideally way off the mark to 3.0v
It may be the case that one battery began with an awful cell yet by interfacing them all together on an equal board you are pulling down the cells on different batteries as well, and have now harmed them moreover.
The main inquiry would be how are you checking the voltage? In the event that you are utilizing a little module cell checker, their exactness is problematic.
In solution to your unique inquiry, subsequent to adjusting the cells ought to be inside about 0.02v of one another.