Electrical Help Please

My wife's BMW battery would die once a month. I trickle charged overnight 2 amps. Brought to AutoZone for a test. They said it was fine. Car was charging fine. This went on for a year. I finally broke down and bought a Battery. Never had an issue since. My opinion was a bad cell or low cell (sealed battery). Good luck and keep us posted.
I had a Taurus that the gauges would go crazy on sometimes, mostly when I started the car. They would flop all over until I turned car off and restarted it. Looked at online posts, lot of people had this trouble and some spent thousands trying to fix it. One guy suggested buying a new battery. I did that (even though the car always started great), and it never happened again. Weird things can happen with batteries sometimes.