the whole point of an alternator over a generator (60's cars and earlier) is that it only runs when you NEED the electricity. When the alternator is running you lose a couple MPG and HP, that's why drag-cars don't have them. The car runs off of the battery, and when the battery gets low, the alternator comes on and recharges it. Alternators monitor the electrical level in the car and turn on and off based on need. So, in order to get this "fuel savings" you run the alternator more. The whole assertion that there's electricity being wasted is BS, that's not to say it might not return more fuel efficiency than it robs, but the fact that they're misleading about how an alternator works makes me think they might be full of BS.
