Is Onstar killing my battery?

Saturday, after sitting for two and a half weeks, my H3's battery was completely dead... again.  It is unable to hold a charge past 2 weeks due to some sort of power drain.  This is not helped by the notoriously bad delco battery they stick in the H3.  I am convinced that OnStar is the root of my problem here.  I live in an area that has really bad coverage and i think the OnStar cellular system constantly searches for a signal even when the truck is off.  My service isnt even active right now.  I have a co-worker that has a canyon and he has noticed the same thing after leaving his truck in a parking garage for a week, his truck is dead.

So, what i really want is to power off this system.  Anyone know if this can be done? 

I don't think your Onstar is active when the truck's off. My dealer did install some GPS locator thing (Inilex, I think) that has it's one battery and can suck the life off of the main battery. Your battery could just be dying. 

Doubt Onstar is the issue or there would be dead Hummers all over the place. What diagnostics ahve you performed to try to isolate the draw on your electrical system?

Wouldn't be onstar.  Do you have any aftermarket electronics installed?  Have you had the battery replaced at all?-

Onstar is not your problem. You either have an accessory draining it (i.e. cell phone charger, radar detector, etc.) or there's a module causing excessive drain. Take it to your dealer and ask them to test the battery, if the battery passes then ask them to do a parasitic draw test on the vehicle. this will give them a starting point on tracking down the culprit. If you do have something plugged in, unplug it when the truck sits for more than a week and you'll be fine.

Could also be a bad voltage regulator............

I've also seen car alarms do it - try just locking the doors vs. using the remote.

My money is on the crap batteries they keep putting in the H3. I am on number three right now at 30,000 miles.

I must have the best car buying luck. ( knock on wood ) I just haven't had the issues other people have.

Thankfully I'm with you 3Hummers. Haven't had any issues like alot on here. However when the battery does go it will be replaced with an Optima Deep Cycle

Definitely replace it with a yellow top or other upgraded battery...when it dies after 4 years of faithful service.

Hmmm.  I'll have to drop it off at the dealer then.  I really dont have any major aftermarket electronic stuff other than a radar dectector which I unplug (it has battery run down protection in it anyway).  I have already had one bad delco battery so this may be #2.  The reason i was thinking my onstar was active while the truck is off is that last summer I was getting vehicle diag reports but didn't drive the truck for 3 months.  So I was thinking that the truck was calling mother ship at some point to send a status.

OnStar does call the truck once a month to get the engine diag.

They can also unlock your doors when it is off, so at some level the OnStar system has to be operating 24/7.  I would say at a minimum its equal to a charging phone but i would guess its more like a constant powered on cell phone (not the new super efficient ones either)

Disconect the + terminal on the battery and check the amp draw with a VOM with everything turned off.
 
Anything over .5 amps is to high and will drain the battery within a week.