Hello, my name is Mike and welcome to JA.
The original battery in your Hummer "should" last 4-5 years. The battery will gradually lose cold cranking ability and reserve capacity over time.
If the battery is typically used alot with the vehicle off, or if the vehicle is used for infrequent short trips, the battery can drop below 12.6 volts from time to time. When a battery is not fully charged, it can degrade quicker.
If you are asking how long your battery should play the radio with the vehicle shut off, then the answer would be about a half hour depending on the variables such as how loud and what else was turned on.
A replacement AC Delco battery is rated for 6 years.
Some Delco batteries are the newer 7 year model Your Hummer may have one of these. Unfortunately, I have seen a lot of failures with these batteries for some reason.
I hope this answers your question.
Thanks,
Mike
All of those accessories can make a difference if you leave the key on a lot with the engine off, but if you are operating the vehicle normally, these items will not affect the overall life of the battery. Your vehicle's charging system is designed to carry the accessory load while driving the vehicle.
Hope that helps.
ASE Certified Technician
20 years experience, all makes and models.