Has anyone ever had a voltage drop in their '02 Civic. I just bought a new battery. As soon as I turn on the a/c, rear defroster, stereo system, and headlights, the voltage drops to 12.5V when on and the belts screech. The belts will only screech once, and won't do it again, and the volatge will go back up to 14.32V

 

Try tightening the alternator belt.

 

After the belt is tightened or replaced so it doesn't screech, still expect some voltage drop at idle with everything on. If you have large amplifiers in the stereo system and require full performance at idle, consider installing a high-output alternator.

 

^ x3
and check your battery terminals... if the wires are corroded or dirty clean them get all that corrosion off the terminals. and have your alternator tested out at autozone with it on the car. it might be getting weak.