You set the charger up to let you discharge one battery into the second battery that is charging and you can use the full discharge current available to the individual channel for the 4010 (idk what it is off the top of my head as I have a 406 as you can see). Here you can see my 406 discharging one battery at 39.8A while charging the other at 35A. Additionally, because this is a setting in the discharge parameters you can charge and discharge on either channel. Instead of selecting the "resistor or bulbs" setting, select "charge battery" instead. You start the discharge first, and the charger will wait for you to start charging on the other channel. This is what makes a dual channel charger so much better than two single chargers. Well, that and the ability to cycle batteries without having to disconnect anything or touch the charger mid-cycle.