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.

I heard in AZ people have to replace them yearly because of the heat. Check your ground wires for shorts stuff drawing to much power

Hi I'm guessing here you have never come across the need to change a battery every 3-4 years before caused by suphide build up in the battery itself. This crust builds up over time due the the battery being charged up and discharged over a period this crust build up on battery plates. With in it. So every 3-4 years you need a new battery.
oh yes some do try to combat this with pills dropped in to each cell. Well it sort of works for a few weeks. The result is alway the same a new battery.
Ford cars are also well known for parts that don't last long like alternators they are not well made and don't last long either. So a ready supply is always available.