Thanks RapidRobert and everyone else - I haven't had time to do everything suggested, but the problem seems to have gone away.

The battery is still real strong (only about 2 years old). I checked carefully for shorts and cleaned all of the connections when it first happened - battery, VR, bulkhead, etc., but I didn't think that solved the problem at first.

Since then though, with short test drives it has not acted up. So I took I just took a nice 60-mile cruise, and everything was great.

I'll be keeping an eye on it, and will keep you posted if it happens again.