2007 GMC Sierra 1500 Pickup Owner's Manual - Page 253

Battery Warning Light If this light comes on when the engine is running, there could be a problem with the charging system. Voltmeter Gage When the engine is not running, but the ignition is in RUN, this gage shows your battery's state of charge in DC volts. The battery display will also stay on while the key is in RUN until the engine is started. If the light stays on after starting the engine it could indicate a problem with the generator drive belt, or some other charging system problem. Have it checked right away. Driving while this light is on could drain the battery. If you must drive a short distance with this light on, it helps to turn off all your accessories, such as the radio and the air conditioner. While the engine is running, this 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. 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 at an idle for an extended period. 253