2000 Crown Vic cold start/battery issue.
While i'm driving my battery guage will dip to extremely low if I have the radio on, the headlights and the heat blowing, this seems to be an alternator problem, but i've had it tested along with the battery and the starter at autozone, no problems detected at all. The battery is used, but in good working condition, the alternator is fairly new, and the starter is still factory. The reason i add the starter into this post is because I work as a security guard (in my own car) where i spend a lot of time 8 hours+ per day, and if my car is not running with the radio on for 15-20 minutes, the battery dies just enough to where my car is unable to start. Everything inside my car is factory, so im not drawing unnecessary power from the battery, so i ask all of you, what could this problem possibly be?
I have noticed some build up on my battery posts, but nothing too excessive, so i've been keeping them extra clean every time i get a chance. Is my only option to buy a new battery? Because so far this Michigan winter is kicking both my cars ass and mine haha.