Funny you mention this...just this morning my voltage dropped down to 13.4 and held there until I got to work (15 min at 14.1, 15 minutes at 13.4). I did one stop/start cycle, right before my ramp, to see if that did anything and sure enough it popped back up to 14.3.Once your batteries get fully charged you'll see the voltage dropping some. I just did a 4 hr ride last weekend in my car and after a couple hours of daytime driving voltage was down to 12.6-12.7. at a steady cruise. Your post got me curious to see what my car was doing so I would occasionally put the voltmeter up on the display.
I am one who rarely allows my car to stop/start. I just feather the brake pedal just enough to not engage the system, I hate stop/start.