Ooj-To answer your question your charger will discharge at 20 amps to take the pack down to 5.4v/p or .9v/c.
A tray simply takes each cell individually and equilizes them to be even.Now in MOST cases NIMH dont have memory but it's been proven GP3300's do.
GP3300's actually LIKE to be deadshorted.They will gain voltage,lower internal resistance at the cost of 12-25 seconds runtime.This will NEVER hurt you unless running mod sedan,oval.
In all offroad,spec touring,stock touring,or most 1/12th scale it will not affect you in dumping being runtime is crazy now anyway.
The Octane 2 by Integy or the Trinity 2.0 or 2.5 are the ONLY 3 trays safe for Deadshorting being the bring the cell down to 0volts.
The Rayspeed,other integy trays,Promatch tray and others all cutoff at something short of 0 safely.
When using the Octane 2 or Trinity 2-2.5 you dont have to worry when the lights go out due to deadshorting.The resistor will keep them from reversing.
I charge at 6.0amps at a .05 cutoff on my 3300's.If im charging outside I lower the cutoff to .04 or .03 depending on outside temp being 95 or above.Being it's already warm outside it simply cuts the cell off at a safer level.I run the pack.Discharge at 20-30 amps depending the type of racing.The discharger I use either it be a charger with discharging features,Lights with a cutoff or a Integy Reactor all cutoff at .9 per cell.Then I put them on a Octane 2 tray and bring them to 0.I leave them on about 2-3 minutes after the lights go out and solder a wire from positive to negative.Take off the tray and store till the next weekend or every other.The packs have been great and been using them on a regular basis since March.Almost 9 months and strong as ever.
SMC's driver at the october race won with 7 month old packs.Very UNusual for a team driver racing onroad to be using packs with that much use on them.He deadshorts and loves it.As a mainly offroad driver TRUST the Onroad oval guys.They KNOW how to care for batteries.
Hope this helps
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