2008 GMC Envoy Owner's Manual - Page 171

Voltmeter Gage When your engine is not running, but the ignition is on, this gage displays the battery voltage in DC volts. Readings in the low warning zone may occur when a large number of electrical accessories are operating in the vehicle and the engine is left idling for an extended period. This condition is normal since the charging system is not able to provide full power at engine idle. As engine speeds are increased, this condition should correct itself as higher engine speeds allow the charging system to create maximum power. You can only drive for a short time with the reading in either warning zone. If you must drive, turn off all unnecessary accessories. Readings in either warning zone indicate a possible problem in the electrical system. Have the vehicle serviced as soon as possible. When the engine is running, the gage shows the condition of the charging system. The gage may transition from a higher to lower or a lower to higher reading, this is normal. Readings between the low and high warning zones indicate the normal operating range. The voltmeter gage may also read lower when in fuel economy mode. This is normal. 3-37