by 88formula » Wed Mar 29, 2017 11:20 am
Sounds like voltage drop. If you have a D.V.O.M. check voltage from battery 1 negative to block, as close as you can to the starter. Then from battery 1 positive to positive stud on the starter. Shouldn't have move than 0.5V when you ad the 2 together.
Do the same on the second battery.
Where ever you get a high voltage reading, you are loosing cranking curent to resistance. Clean cables at batteries, ground points, and starter.