Wayne, balanced batteries become more and more important as amperage increases. You can get away with murder at 40 amps yet have big problems powering a huge load with a huge inverter. Place the positive charger lead on one battery positive and the negative on any other battery negative and call it quits.
Much more important is to insure terminals, posts and the copper wire inside the cables is in excellent condition and shiny bright. The area where copper wire strands are crimped inside a battery lug are hidden from inspection and can cause a lot of problems.
