well, depending on the tray...they will all basically check the voltage, and once the cell's voltage reaches that level, it will shut the discharging of that cell off and continue with the other cells until they are all done. and also, some trays go down to 0.0v not just .9, like I discharge at 30 amps using my Integy mini discharger or my GFX, to 5.4volts or .9v per cell, then I put them on my integy tray that brings each cell down to 0.0v