I'm familiar with the afterglow period, and in fact my sudden increase in voltage occurs well after I hear the glow relay click and see another (smaller) brightening of my dash lights, etc.

On these winter days I don't crank the starter until the afterglow period has just ended - right after I hear the relay, etc.

But I understand what the pros say - the alternator should charge even at idle - mine doesn't - but it charges just fine after it "wakes up". Now I've just got to see if I can pin the wakeup to a certain rpm, or, change the brushes, etc.

Rgds,
Chris W.