The ECM/PCM will vary the charge voltage dependent on the Battery Temperature, usually a simple temp sensor in the battery tray. The colder it is, the higher the charge voltage "set" by the ECM/PCM.
Again, I'm a Commander Newb, but very knowledgeable on vehicles and Chrysler Vehicles in general, if I'm wrong, please correct me, this is the way Chrysler does it on just about all their vehicles.
Basically, I have observed, below freezing expect the full 14.6Volt, Hotter Summer day, expect the 13 some volts.
Yes, as the battery charges, it resistance will change, and that can vary the voltage depending on how well the alternator can supply the required current. With a good battery and charging system, I have seen almost no change after start to driving for hours, system voltage varied by temperature only. (Even though the sensor is in the battery tray, its seems to vary with the Outside Air Temp pretty closely.)
A bad battery can draw way too much current and that will drag down the system voltage, which the low voltage can cause all sorts of electric items to operate strangely. That is why you'll hear stories where people replaced the battery and suddenly all of their electrical gremilins were gone.
Most of the vehicles from the 90's on, with the ECM/PCM smartly controlling the system voltage, do a much better job holding voltage. I have an underdrive pulley on my '99 Neon R/T, and the charging system holds voltage, except in very cold weather with everything electric item on in the vehicle and the motor at idle, at that point, voltage will start to drop as it drains the battery, more than a few minutes at idle under those conditions and I get the charge light with voltages down at 9 volts if I don't rev the motor with the clutch pedal in.
Last edited by Mongo; 12-13-2010 at 08:44 AM.