I agree with G Benz, you need to drive the car. Starting the engine and letting it only idle, won't recharge your battery. Also, your oil will warm up, create condensation, you'll shut off the engine and that moisture just sits there. You should get the oil up to operating temp, to allow for the is moisture to cook off. Once a week or so, take your ML out for a good 30 min. drive, also keep the gas tank full. This also will help prevent moisture build up.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member