I bought this car on Saturday with 105, 000 miles and it has an aftermarket Pioneer head unit that you can play music through iphone or ipod. The first day I got it, I sat in it without turning the car on just so the battery turned on and I played some music through my iphone. I did this for about 10 minutes and I was fiddling around with the bass setup and reverse speaker and or normal speaker, and the hertz from 50 hertz to 125 hertz. The next day I did the same thing and when you turn the car off you have the option of taking off the head unit (It slides right off) So I figured sure Ill take it off and put it in the glovebox, So I did that and locked the glovebox. Next day I go to get plates to register the car, and the car wouldnt start, my dad immediately told me that I shouldnt have sit in the car and played music. So we charge up the car with a battery charger, the black terminal (negative) had a bunch of dirty stuff (I'm guessing corrosion) around it so we cleaned it up with some terminal battery cleaning tool. Then it started up fine. So we took it for a ride and I plugged on the radio when the car was off, then I noticed shortly after it said Change alternator error on the dash and it was dimmed. So I pulled over switch seats with my dad and he drove it back home, on the way home the setup on my head unit was going crazy switching bass from -6 to +6 without anybody touching it, So I slid it right off and put it in the glove compartment. Came back home charged it, and then took it for another ride without the radio. Please help me, Do I need a new battery or a new alternator, or maybe should I get it checked out first by a trusted mechanic?