Sorry, removed the fob from the key ring is what I meant. After testing it for a week in foil, I'll re-inspect it for possible shorting and stuck buttons. I retested the battery with both multimeter settings and now they both show 12.9v. I believe the difference before was due to the fact that the first test was after the acc switch had been on (draining power) and the second test was after it had been running to test the charging system (adding power). I will continue to test it every couple hours to see if there might be some sort of parasitic drain on the battery. Yes its an HHR

 

What made me wonder was the typo. Some other cars have the fob integrated into the key. I doubt the foil is doing anything, removing the battery would.

 

Ok, I'll remove the battery in the fob instead. Now I have been tracking the car battery voltage every few hours and it has been dropping. In total it has gone from 13.0v to 12.7v over a period of 19 hours. I'm no battery wiz, but this seems to indicate some type of power drain rather than a defective cell in my new battery?

 

Not necessarily. If it doesn’t go below 12.6, it’s probably fine.

The acid test (pun intended) is to disconnect it and then watch for the voltage drop. See how far it goes. As best I can tell it’s still acceptable if it stops dropping at 12.6, but a new battery should hold out at a bit higher.

Full disclosure, I’m not a battery wiz either.

 

Fully charged is 12.7. Don't worry about it if it doesn't go below 12.5.
Does the car have Onstar installed? If you don't want it or bluetooth pull fuse #24 on the BCM.

 

Pulled the Onstar/XM fuse. Thanks for all the tips everyone! I'll monitor it over the next couple weeks and then try to reactivate the fob.

 

We shall await your update!

 

Update:
After 3 weeks with the battery removed from the fob and no random alarms, I replaced the battery in the fob yesterday and made sure the panic button was not somehow stuck (and checked that it unlocked the car). Sure enough, about 6 hours later the alarm started up. Removed the fob battery while inside the house and the alarm shut off.

 

Did you look at the carbon contacts on the keypad and the traces on the PCB?

 

Yes, and they look normal. Next I will try a piece of paper separating the panic button contact from the PCB, when I will be home all day.