There's a fuse on the back of your head unit. You will need to pull it out and replace it.
The reason for changing battery? A little more info might make it easier to locate the problem. CD-Changers have an inline fuse if its aftermarket.
The power supply to your Cd changer is a constant 12 volts run directly to your battery. The radio meerly turns on the controls to it. You should be able to remove the cd's without radio power.
Mitchboogie
July 2005