It's gotta be the lights. Check this out...

With the car OFF. I turned on the lights. Starting voltage 12.51v. 5minutes later. 11.6v.

Even though the battery load tested OK, I think I'm gonna go to Costco, buy a new battery, try it and if it does not fix the issue I'll take it back. Can't hurt.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k