Circuit/System Description
WARNING: This page is about a different car, the 2011 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.
With the Ignition OFF, the body control module (BCM) monitors the battery voltage to make sure that the voltage stays within the proper range. If the battery voltage is too low the BCM cuts several electrical circuits depending on the charging condition of the battery.