Battery Gage
WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The instrument panel cluster (IPC) displays the voltage as determined by the regulated voltage control (RVC). The IPC receives a GMLAN message from the BCM indicating the battery voltage. When the engine is ON, the gage should be between 10-16 volts. The gage will default to 0 volts if the IPC detects a loss of communication with the BCM.