2009 Suburban came in today with a complaint that the instrument cluster displayed a message "Service charging system and/or battery". Customer indicated the voltmeter needle displayed about 13.5 VDC (and usually was much higher). This vehicle has a "main" battery and an "auxiliary" battery. When I opened the hood there was a strong odor of sulfur or sulfuric acid. I used my FLIR thermal camera and captured images of the main and auxiliary batteries. I have attached a thermal image of the auxiliary battery. [Failed Battery, Charging light on] In the image you can probably see three of the six cells are very hot. The second cell in the battery appears to have a hot spot about 225F, the entire battery was near 200F. Additional images that I captured indicate how hot the alternator was at this time and the the positive cable (in parallel configuration) was warm especially at connections.

After testing both batteries and confirming battery "date" codes several years old, we replaced both batteries. The charging voltage returned to over 14 VDC and the alternator was not "working so hard". The instrument cluster no longer had the warning message.

Mark from Colorado

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