2005 GMC Sierra issue

Hello All, I have a 2005 Crew Cab GMC Sierra Z-71. I love the truck, but have a major issue with something the local service department and GM says is
normal. When I leave the truck parked for a long period of time (so far 20 days and 21 days) the battery dies. I travel with the Air Force frequently, so this is becoming a real aggravation. The dealer says it is normal for the battery to drain in about 2 weeks due to the 7 onboard computers. My 1997 Camaro SS sits for longer than that sometimes and starts nicely. I had a 2002 Silverado Ext Cab Z-71 and left it for sixty days once with no problems. The only difference I can see is the GMC has OnStar, and the Bowtie didn't! I know some things had to be changed from the 2002 to the 2005 models, but enough to cause this?!! Anyone have opinions or similar experiences? The dealer changed the battery both times I took it in! I did notice there were a few new cars on the showroom floor with the hood up, and a battery charger connected! Thank you in advance for any replies.
Jerry
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JP wrote:

The electrical was completely redesigned in 2003, the radio for example is turned on by the BCM, but a lot of things turn off after a few minutes so I wouldn't think it would drain the battery that fast, but I have never parked my 04 for that long. Unhook the battery and put on an ammeter and see what the drain is, wait long enough for the RAP to shut off. I've heard a lot of car dealers have little solar panels that sit on the dash on lots to keep the batteries from draining too low so it could be normal now a days.
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