I am having an issue with my battery being completely dead after the truck is parked overnight. It's a 2008 Yukon SLT with about 75k on it. The battery is about 2.5 years old. This has happened a couple times before, I thought it might be that the kids left their phone plugged in to the chargers. But this time that was not a possibility. It has sat for longer periods without an issue, and it appears to be sporadic. Any help would be appreciated.