rsa,
Hmmm...I'm starting a rebuild on my alternator this afternoon...it will be interesting to see how this affects it. Interesting to me that a new battery fixed the problem. Once the starter engages and the alternator comes online, the voltage regulator should maintain voltage at 13.5-14.5. Battery should just be there for starting unless, like you say, at low rpm's the alternator drops offline momentarily forcing the battery to carry the load temporarily. I'll certainly let everyone know if the problem is related to this.
Ryan