yeah my last 2 GM cars (a '94 and a '89) you could test the alternator by starting the car and unplugging the battery. The car would run fine without the battery. Although I suppose you're right that when you run the AC and the radio and the lights, it might draw some from the battery, but I know that the alternator actually produces more energy than the car needs, because it recharges the battery while it runs the car. Otherwise, you'd need a new battery every week. But once again, I suppose there could be gains from this. I just wish I understood advanced electronics enough to make sense of it all.