First off my truck is a 2000 7.3 Auto 4x4 with a Gearhead chip. I also have an exhaust and intake. So i have had this problem and have been dealing with it for about 2 months and it has just gotten progressively worse. Now when I turn my key on the batt. gauge in the dash jumps to 12v within a 1/4 on a sec. it drops to around 10.5v after about a min. and a half it jumps back up. I then try to start and batteries are dead all that happens is a relay clicks. batteries have been load tested good and all new terminals (solder and copper crimp on done by napa). I have checked ground wires and I used a voltmeter to confirm grounds are good.