Battery gauge
WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet 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 gauge should be between 10-16 volts. The gauge will default to 0 volts if the IPC detects a loss of communication with the BCM.