I have 4 guage wire(all that was available) running from the pos terminal in the front to the positive terminal in the back, with 2 inline fuses. Then I have the second batt grounded to the chasis. Both of my amps are also grounded to the chasis. Then wired up the amps' power cables also to the second batts positive terminal(same terminal that first batt is connected to). Im not sure where i went wrong. I tested the second batts charge with the car on and off and it stayed the same, while the first batt had a 0.6v increase. So I know my alt is good. And the system hits lovely until the second batt loses juice. Im just looking for some help before my second batt loses life from dying and recharging(done this like twice). Any help is greatly appreciated, been looking for an answer for about a week now.