I assume that "chg" stands for "charge" and not "change". My electrical engineering class has uses 6 Battery Tenders (check out this link) to charge 6 batteries in an electric vehicle. You just connect each battery tender up its own battery. You don't even need to remove the batteries, just disconnect the series connection between them. The problem is, 6 chargers at $125 each is alot of money. I would check out the battery tender website for mulitple battery chargers.