2010 Ford Fusion mystery annual battery drain. What is killing my battery?

2010 Ford Fusion mystery annual battery drain. Last year I found my cars battery had died. I took the battery in and they charged it and tested it and told me it was good. I stuck it back in assuming it had to be the alternator and my battery would soon be dead again, but no it didn't die… Til a year later it happened again last week. I took it in they charged and tested it and said it was fine. I stuck it back in and it has been fine for a week now. What is going on? No lights were left on. The only two commonalities are 1 it was around the same time of year. (a/c?) 2. I had an male-male audio cord plugged into the aux. (nothing attached unless I was driving) from what I heard that does not draw power.

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