Most car batteries are actually 14.4 volts, regardless of what the specs on your car's electrical system might say. But there are cars (economy usually) whose batteries do not run at that voltage, and instead run closer to 12 volts. This is how it was explained to me by mechanics and car stereo professionals in my area.


A nominal 12V battery (6 serial connected lead-acid cells) has a "idle" (at rest, no current drawn or pushed into the battery) voltage of ~12.6V.

To fully charge the battery you need (depending on temperature) between 13.8 and 14.4V delivered from the alternator.

So a 12V rating is typically applicable when playing with the engine off, or possibly at low idle where some alternators don't produce full effect, while the 14 or 14.4V rating is applicable for when running the car. Some amp manufacturers list power at 13.8V as that is a fairly realistic target voltage at an amp in the rear of teh car considering losses in the wiring.

To get full voltage to the amp you need proper gauge wiring. It also helps some to upgrade the "big 3" wires under the hood: battery- to ground, chassis ground to engine ground and battery+ to alternator+.

/Michael