Interesting post;

I noticed the exact same problem crop up last week on my 1990 Honda
Civic wagon. The red battery light on the dash would flicker
intermittently ont the highway, and sometimes stay on as long as 5
minutes. The battery is about year old. Now that I am back in the
city, it may flicker a bit and come on for about 10 seconds.

After a voltmeter test, it shows that the alternator is charging the
battery fine when the engine is running, but under full load (radio,
heater, defroster, lights), it is not. Is this something I should be
worried about?