larger converter wiring needs

[logbuilder]

I have a 2013 Coachmen Chaparral 327RLKS. I am changing the standard Converter to a PD9280 because instead of having only one 12 volt battery I have installed six 6 volt 220 amp hour batteries and a 3000/6000 watt pure sine wave inverter for a total of over 900 Ah capacity. The new converter/charger will charge batteries much faster among other good things. My queStion is about necessary wiring changes that will Need to be done. I am aware that I need to have a 20 amp breaker for the new converter. Currently there is 6 Awg wire being used but because of the increase in batteries and discharge amps what gauge of wire should I replace the existing with? I have Figured out which wires go to the DCpanel and where thewhite from the converter goes. Addition to the size wire question how do I determine which red from the converter is the red that attaches to the battery switch? Tand then of course how tohanks