I actually meant to transport around in the car itself. Rather than the huge number of batteries required to get a decent range, a hydrogen fuel cell is only about the same size as a normal fuel tank (that's my understanding, but I'm open to correction). I now know that you also require batteries as a buffer between the hydrogen and to power the car, but surely not in any number near a pure electric car?
They look to be about the same size as an ICE:
I think buffer battery size would be dependant on motor demand and the generation capacity of the cell.
It looks like future fuel cells will use Nano technology to improve efficiency (while minimising the amount of Platinum and Palladium catalyst required). The same technology is being used to improve Li-ion battery design for pure EVs [edit - pajo1981 got there before me, and more detail, in the previous post ] - hopefully competition will accelerate development and improvement of both leading to truly practical ICE alternatives.