From what I've read, alternators are only about 50-60% efficient (not including belt losses which I believe are only around 1-3%). Also, from what I've read you can be using up to 25A just at crusing speed. This calculates out to 300W of power needed, and at 50% efficiency we are looking at 600W of gasoline power which is the equivalent of .8 horsepower. At low speeds this could be well in excess of 10%. At higher speeds it definitly can be less than that (depending on many other variables).
Now you just have manual daytime running lights Ben.
