I think that 6 volts is below the minimum voltage requirement for the ps2/ad20 (I could be wrong, it should be printed on the ps2/ad20's coverplates). You could wire the 2 6 volt ecocharge batteries in series to produce 12 volts, but that's a lot of lead to carry around. Better bet might be to sell the ecocharge battery system and pick up a wallmart-style 9v lithium ion battery (around $30 via ebay) which would be a fraction the weight and would power your rig for a REALLY long time (literally all day)