Voltage regulator went bad on the W124 causing dash indicators to light up and the radio output level control to go nuts.

In addition, you could visually see (and smell) the battery venting! Measuring output voltage at the battery yielded 17.5!!!

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car