2005 GMC Yukon Owner's Manual - Page 192

Battery Warning Light If this light is displayed when the engine is running, you may have a problem with your charging system. Voltmeter Gage When your 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 with this light displayed could drain your battery. If you must drive a short distance with this light displayed, it helps to turn off all your accessories, such as the radio and the air conditioner. 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. 3-42