I recommend you start by cleaning the battery terminals/cable ends. Look critically at the cable clamps because I've had more than one OE clamp crack resulting in a poor or inconsistent connection (if cracked, replace). Also check the opposite ends of the cables to be sure they are securely fastened and with good contact. There are some other flat grounding straps in the engine compartment as well...check that they are secure with good contact as you see them.
Underestimate me, that will be fun.
GREEN WORM RACING--since 1959
These are my opinions...YOU are responsible for YOUR decisions and YOUR outcomes...AND, my not arguing with you does not indicate agreement with your opinion.