I saw on one of the forums something about measuring voltage through the cigarette light/power outlet. I just cannot find it.

Does anyone know what the voltage is supposed to be in the following situations? Perhaps there are other situations as well.

Ignition off
Ignition on-not running
Ignition on- running at idle with low beams on
Ignition on- running at idle with low beams on, seat heater on
Ignition on- running with at idle low beams on, seat heater on, fan on level 2 or 3
Ignition on- running with at idle low beams on, seat heater on, fan on level 2 or 3 and rear window defroster on.

I have noticed my idle (in traffic) when I turn on the rear defroster the idle speed drops, ever so slightly, and the dash lights dim slightly. Not sure of the significance and how to really test. BTW, my 22 month old battery is the Autozone DURALAST 49-DL recommended here.