I've noticed that the voltage when driving seems to alternate between about 12.7V and 14.5V. It seems to do this in steps - that is, there seems to be no intermediate value between the aforementioned ones.
The battery seems fine. It's reasonably new.
Is this expected? Is there some kind of regulation going on that drops the charge rate when the battery is topped up?

I ask, because I'm taking the car to France in a few weeks time, and I don't want it to fail on me!