It’s quite common on GM vehicles, but make sure its not the battery itself. Overtime, batteries get old and can’t hold a charge for a very long time. Leave it disconnected overnight or for a day, hook it back up and see if it starts. You can also get it tested at an auto parts store as well. If the battery checks out okay, then you might have to pull out more fuses to accessories to see whats draining it. Do you have anything aftermarket on the car?
Parasitic Drains are the worse, i spent days trying to figure out what caused mine until I found out it was a bad battery.