my big 3

Just got done swapping in the 4g for the 8g on a quick 30 min. break. I started the car up and noticed the voltage display on the cap. read 14.7 - .8 instead of the usual 15 at idle. Lights on, no difference. Didn't turn the music on. Ran down the road about a 1/2 mile then back. The gauge still read 14.7. If I ditched the cap., then grounded the rear bat. better, then re-ran all my power wires -I could cut out like 3-4ft. from the front bat. to the rear one-, then everything would perform radically better and more efficiently? I would still like to have a voltage display for quick diagnosis -more like to have some sort of lights back there... -or would an amperage display be better for quick diag., of possible.?