The only two ways to prevent cell reversal is to not discharge deep enough that one cell becomes completely discharged while the others still have charge in them. If this happens the ones that still have charge in them must still send their charge through the dead cell (because the cells are in series) and the dead cell receives a negative voltage from the ones that still have a charge. The voltage of the pack itself will still be positive so putting a diode here will do nothing. The second way to prevent cell reversal is to isolate each cell electrically like a discharge tray does.
As far as ceramic discharger, I guess you mean a ceramic resistor. The rate at which it discharges will depend on its resistance and the voltage in the pack, its not a constant discharge rate.
For example the resistance is 7.2 ohms and lets say you pack puts out 7.2 volts when connected to it because of ohms law V=IR we can get I=V/R so it will be discharging at 1 amp. Now as a pack discharges its voltage drops so the discharge rate will decrease.
Diodes in discharge trays don't have anything to do with cell reversal. Because in a try the cells are electrically isolated from each other the max any tray can do to a battery is bring it to zero. The diodes prevent this because they have a forward voltage drop of arround 0.7 volts. This mean for any current to flow there must be 0.7 volts or more applied. Diodes were added to discharge trays a few years back because dischargeing batteries to 0 volts can sometimes lead to a pack that likes to false peak early in its charge cycle. Now with NiMH cells they also benefit your cells because if you take a NiMH cell to zero it may never take a charge again, but it has nothing to do with cell reversal.
Hope I helped out.
Last edited by patcollins; 04-17-2002 at 04:21 PM.