Propane fuel cell the size of watch battery

They run on
poo and even
blood, but most
fuel cells currently run on methanol.
Now, engineers at the California Institute of Technology report success in developing a propane-burning fuel cell almost as small as a watch battery. Why propane? Well, besides the lovely skunk's-ass aroma, the larger molecules pack more energy and can be easily stored as liquid rather than pressurized gas. So a small cartridge of liquid propane could feed a fuel cell for days — or for that matter, grill-up some hearty nanobot wings. Alas, you won't find these in the check-out line until well after Father's Day.