Why not just downsize ?
This may have already been covered or maybe is irrelevant so apologies in advance, I work in IT so I haven't followed the discussion on papers, watts etc.
I notice on my new "ride" (1 Litre, 3 cyl Petrol) that the battery is, well, tiny. I mean really tiny. I have an old style MGB which was designed with 2x 6 volt batteries of which I have 2 new ones, but the one in my new car is about the same size, if not smaller, than one of those.
Assume my Aygo also has a small alternator as it only has 3 cylinders and 998cc then surely there is scope for a reduction in size rather than a full elimination in other vehicles ?
My though line is this - take a typical car which has been stripped for hypermiling - e.g. a Civic or something else. If you have reduced the electrical load (removing AC, extra lights, etc.) then you can live with a smaller (Aygo, but also Chevrolet Matiz) sized battery which also saves weight, and also a smaller alternator because anything bigger is a waste of energy as the battery is so small.
That way you get the benefits of saving on the alternator load vs what the engine had rated originally, less weight in a smaller battery but also get the convenience of a constantly charged battery whenever you use your car - like a conventional car.
EDIT - PS - plus this is nuts and bolts mods which are the simplest.