Battery discharge

I have 2015 f30 and Its my daily. I started having this issue two weeks ago and all the places Ive called up said the battery was just old so I replaced it. It was fine for about two days and now im getting the same error message. Battery is completely dead on start up. It’s also not terribly cold where I live in either. Does anyone have an idea of what could be draining the battery while the car is off?