battery/alternator whackness?

[chmercer]

somthings up with my battery and/or alternator.. right when i start my car the volts are at like 11.8-12.1 (pretty low) and if i rev my motor without any load on it my voltage will go up to like 14-15 and interior lights will get brighter, then the voltage will go back down to shitty levels. i took my alternator to autozone and they said it was good, and i charged my battery overnight and it says its fully charged, so i dunno what the hell is up with it. the car starts right up and the car drives like normal, but i just dont like the feeling of having shitty voltage and getting stranded. has anyone had a similar problem?

[NIK90s13]

Check all your grounds. Motor to body, batt, batt to body, everything. Make sure they are clean and tight. If you are happy with that, i would think it would be the alt, I know you had it checked, but what you are describing sounds like the alt.