battery help

[bucks]

I have a problim, the battery in my H2 keeps dying, if i dont drive it it will last about 6 days before it wont start the truck, i took it to the dealer and he tells me that is normal. well now it will last onlt 2 days before it dies. does anyone have any ideas of what is draining the battery or if i need to contact Hummer Rep for a replacement, the truck is an 05 H2. any info would be appreciated.
thanks