alternator or battery?

[95mitsu03]

here is my problem, my car will be running and I have the heat, cd player, and lights on. I am losing a lot of voltage. when I step on the gas or driving the voltage will go back to normal, but when I just let the car just sit, the volt will go down like crazy. my cd player actually shuts down because of this. what is the issue with my g? has anyone had this kind of shit happen to them? is this expensive? could it possibly be the voltage regulator on the alternator? what is the rating on a 7 g alternator? can I improve it? sorry for the long post but I just need some questions answered, I just don't want to get stuck and stranded some where. HELP!!

[Dark7GHawk]

Go to any AutoZone and get a free electrical system analysis. They will tell you exactly what is wrong if anything.