I'm starting to see a charging system problem and hoping to get some ideas where to start, since it's a marginal rather than total failure at this point. Last year when I was doing some night driving (unusual for me in this vehicle) I noticed my headlights seemed to pulse a bit, getting dimmer and brighter at a fairly rapid rhythm while idling at a stop light. I checked the voltage at the battery with a voltmeter and all seemed well, so I thought nothing more of it. That may or may not have anything to do with what I'm seeing now, which is...

When I got on the freeway yesterday, battery idiot came on. It gradually flickered off as I decelerated, and stays off at surface-street speeds. Accelerating to speeds above 45 or so causes it to come back on.

Possibly related is that the car, though it turns over just fine, seems to be more difficult to start over the last few days. It revs like a champ, but is slow to fire and start running.

What does this sound like to you? Is this the way some alternators fail? Voltage regulators, maybe? Any intuitions would be appreciated.