I did some searching, but I'm not sure what's wrong.

My batt. is coming on...
Car starts fine, seems to be holding charge. Batt. light at first just flickered on at higher rpms, now 150 miles later is flickering almost all the time and stays on a higher rpms.

I had the guy at autozone test the batt. and although it seemed to have 12 volts with the car off, I didn't seem to be putting out more than 12 with the car running, but that was only at idle.

Anyway I'm not sure what to replace but I want to fix it before I drive it more. If anyone could shed some light on this I'd appreciate it! Thanks
-Peter