That sounds like a battery problem more than a charging problem. Did the installation of the CD player coincide with the problem? A bad battery can kill an alternator and a bad alternator can kill a battery. People can get stuck in vicious cycles. I think the best test is to disconnect the battery, charge with a charger (as opposed to the car's alternator
) , and then let it sit for 12-24 hours to see if it holds the charge. The battery tester that draws a high load is best.
Robert