My old Sony system used to do the same thing but only if you left the facelift in - and then after 2 days the battery in the car would be flat, then changed to JVC and almost always took out the facelift and was never a problem, but last week I got a fancy car stereo that takes CD's, USB Sticks sand SD Cards and after 2 days the car battery was flat.
So I figured the only way to tell if it's the stereo or battery is to try a new battery and see what happens. (without using a meter to test the current being drawn when the car is idle)
I did however remove the car battery and hook it up to an electronic charger with 4 LED lights that show the 4 stages of charging. Left it on for 15 hours so far and it's still on stage 2 - it works backwards and starts on stage 4, then 3 until you get to 1 and then you know it's fully charged, but it's still on 2 after 15 hours and you can hear a lot of bubbling sounds from the battery.
The battery is 6 years old so I figure it's time to replace it anyway but I was wondering what might be the problem with the battery. I have turned off the charging now as it didn't quite sound right and wanted to make sure there wasn't an explosion or anything like that.
I've replaced it with a new Bosch Silver Battery which was only £30 and will probably hang on to that. I'll have to go a few days without using the car to see if it's the MP3 player draining the new battery as well.
But any insights / advice / similar experiences into the world of car batteries?