Tested voltage at the battery with the engine running this morning and it reads 17.5 volts!!!
So I had to leave the 300E at home and take the ML to work.
Unless some elves replaced all of my courtesy lights with halogen bulbs, it seems like a overvoltage problem.
Engine eletricals seems to be doing some sort of cyclical switching as the idle revs up, a click is heard and then the idle goes down, another click, idle goes back up, etc. etc...
I turned on the headlights which were extremely bright (again with the elves), then back to normal as the engine "click" was heard, matching the cycles occurring with the engine.
I will have to test the cells this evening, but I sure hope it's just the battery. It is a good quality unit and was purchased in the fall of 1999.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car