I am not sure what you are asking. I don't own a DUO. I own 2 EOS0610i chargers and one EOS1210i. You can see a pic of my setup in my gallery. I can charge one pack at a time on my 0610 and 2 at a time on the 1210 using 2 lba 10 balancers. The largest load I put on my ps is when I charge a 6s 2500 on each of my 0610s and 2 3s packs on my 1210i. This means that I am charging 3 seperate packs will a total cell count of 18S or 33.3V.

If you get the right connectors you can charge up to 4 3s packs on the DUO. You will need to wire them with a [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXNKY9&P=ML]series adapter[/link]so you have two sets of two. You will then need to link up the balance plugs using an adapter like [link=http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=6544]This dual 3s to 6s[/link]. If you do everything right you will have 4 3s packs hooked up but the charger will only "see" two 6s packs. Does this make sense?

xsnrg- I am not sure why some chargers require 15V to make peak power but they do. My MFJ ps is adjustable up to 15V but will only supply about 36A. The 40A continous rating is at 13.8V for approx 550W. I am not an electrical engineer or an expert on electronics, batteries, and chargers. I am just attempting to relay the things I have learned over the last couple of years. I know that I wasted alot of money on inadequate products.

Good luck!