Look up the Harrison Labs fluxcap.. I just picked one up and started using it, The bottom post wires to the stock battery (12 volt) and then theres a shared ground between your 12v and 16v batterys, and then the top post charges your 16v batterys. The fluxcap i ordered charges at 17.9 volts, and i raised it up to 19 to try and get max power out of my sundown, not realizing i only gain efficiency over 16.5 volts on the amp.. I need to open the fluxcap back up and reset the voltage, but its a pain to open up with the bolts. I was going to run a step-down and use a external regulator and HO alternator, but this has made it so much easier. Once i get my real system going in here, and not a temp one, i'll make a writeup about how much i love this dc to dc converter.