Recently, i just put a new battery in my benz. after one week or so of inactive use of the car, the car wont start the next time. Since the battery is brand new, i wouldnt think the battery is defective. My mech told me it is possible that my alternator is bad or I have something that is draining it. What are the things that I can check besides the alternator for this battery drain? All suggestions appreciated. Thanks

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2001 E55

2001 E320 Sedan

2001 Subaru Legacy

2006 SLK280

2016 Subaru Outback 3.6