Last Sunday, I installed a new voltage regulator and brush pack. It's a Bosch unit that I picked up from Tasca and I even checked to make sure the numbers were the same. I started the car and the voltmeter read about 13 volts at idle with nothing on. The old regulator had a voltage reading up in the 14's. When I loaded it up by turning on the A/C, blower on high, headlights and radio, the voltage dropped to just barely 12, but it would go back up to 13 or so when I shut everything off. This morning, I started the car and the voltage read around 11 with nothing on, and stayed there. I had a spare battery that I hooked up, thinking it might be a battery problem and the voltage went back up to about 13. I guess my question is, is 13 volts normal? Am I being paranoid about how much voltage the alternator should be putting out? Is my old battery shot?