More than likely it is the terminal clamp. Start with small things first, and work up from there.
I would spend the $5 or $10 for an autozone clamp or two. In fact that's what I've been using for 2 years, without issue.
While you're in there, get some di-electric grease to put on the freshly cleaned terminals. Do both.Make sure all corrosion is gone and they are shiny. Clamp tightly but put NO stress on the terminals themselves.
Drive car for 45 min. to recharge battery. Take back to AZ to re-test battery.