Parasitic Draw or Bad Battery? (GM Truck)

Hey, this truck looks familiar... This beastly Chevy 3500 Dually was featured in the "Reduced Power" case study a few years ago: https://www.youtube.com/watch?v=Z34r2Fra7ig&t=26s This time it came in with some wonky gauges, and a complaint of a DEAD BATTERY if the truck sits for more than a week. Are the two symptoms related? What is the FASTEST and most ACCURATE way to determine if you have a parasitic draw? Visit the PHAD Amazon Store for all your Electrical Diagnostic tools and supplies: https://www.amazon.com/shop/pinehollowautodiagnostics Enjoy! Ivan