do you know where the backup battery is?

how to remove?

through courtesy lights?

pull up the carpeting and it is behind a plastic protective cover. 3 bolts hold it in place, and as ub2slw said, the back-up battery is sitting on top of the OnStar unit. Then just unplug the unit. The green light will no longer appear in the ceiling unit, and I don't know what codes it may throw.

the acutal on-star box is in the passenger footwell under the carpet. You'll have to remove the glove box and the passnenger side kick-panel to get the carpet peeled back. Once you get the carpet back it'll take a 10mm socket to remove the metal bracket that holds everything down. MAKE SURE YOU VAGCOM TO DISABLE THE BACKUP BATTERY.

Is the Onstar battery inside the module? There wasn't a battery mounted above my Onstar unit. MGH

It is out of sight sandwiched inside the Foam pad just below the Onstar unit. If you follow the large harness coming from the Onstar plug you will see a couple of wires going into the Foam. You just undo the bottome nut on the tin braket and pull the Foam out, it opens up to reveal the Battery, Undue the plug, leave the open plug in the foam so it is out of the way and reinstall everything. It is as pictured in the Etka, figure 035-70.

of times, and they probably wanted to make it easy for themselves in the future.