Yep, there ya go. I seem to be getting a lot of flack over the numbers, but even if you peg them and say the combustion is 80% efficient, alternator is 80% efficient, and H2 cell is 80% efficient, you're still substantially better off by simply not drawing the excess power from the alternator.

You can't escape the three laws of thermodynamics:

Law 1 - You can't win
Law 2 - You can't break even
Law 3 - You can't ever leave the game

PS - by all means, if you want to try it, I'm certainly not trying to stop you, my original question was "is there something I've missed" - besides being +/- a few percent efficiency here or there, it doesn't seem so.