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Douglas_Knight comments on [LINK] Waitbutwhy article on the history and future of space exploration, SpaceX and more - Less Wrong Discussion
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What's going on in your first paragraph? How did we get from spaceflight to cars?
Without bothering to read these comments, my understanding is that fuel cells are bad for cars but good for spaceships. Batteries win on energy per volume, but lose on energy per mass. Also, fuel cells can store energy for a longer period of time, but that is relevant to the outer system, not for Mars.
The linked articles cover pretty much everything, from cars to spaceflight.
No, the issue is power density. Fuel cells win over batteries in terms of energy per mass but lose in terms of power per mass and power per volume. Fuel cells are still an order of magnitude or so behind batteries in terms of deliverable power. This is why they are best suited to applications that require power drain for an extended period of time without the possibility of recharging.
It's difficult to directly compare batteries and fuel cells, though, because in the fuel cell the actual fuel tank is separate from the electrodes and can be made as large as desired. In the limit of a very large fuel tank, huge energy densities of 20 MJ/kg or 15 MJ/L are possible with methanol. Compare this with about 1 MJ/kg for the best lithium-ion batteries. However, in the same limit, fuel cell power density drops to near zero.