The difference is all current, load and charging, should enter the batteries BALANCED. Positive on one batt, neg on the other, NOT both batteries grounded separately. Impossible for both to have same charge/discharge action. Negative lead could go to one starter mount bolt for better cranking with cable to now vacated (of batt neg leads) ground junction in center of crossmember to pick up rest of the smaller loads. Pictures and numbers to follow after I get air leaks solved.