A lithium ion battery out of a Dreamliner ... That wouldn´t be very reliable, would it?
You would only run the low risk of bursting into flames, it'll be ok. And worth it, for 0.01e- read noise.
I do suspect, however, that viable fuel cells the size of current batteries will arrive soon enough. And provide much more power. They will probably cost a good bit more than the average battery, but such is the price of progress, I guess...
Fuel cells...you mean those that use natural gas? Or what type of fuel cell are you referring to?
The only time (so far) that I have been able to visit CA...I traveled with my brother to silicon valley, to check out a fuel cell that was about to be purchased by the university my brother worked for at the time. Funds for this purchase came from various places (some public). I think they paid a total of $8 million. It was spec'ed to produce only 4000 to 5000 watts...but for the brief weeks it actually worked at all, it produced about half that. It is now gathering dust, does not work at all.
A fuel cell is simply an energy cell that produces energy by controlled chemical reaction. Technically speaking, batteries are a type of fuel cell, albeit ones that do not produce much energy. Basic fuel cells generally oxidize hydrogen with oxygen in some controlled chemical process that ultimately produces water (the reaction is obviously not direct, otherwise that would likely cause an explosion), which is an energy-producing reaction that can produce a lot more energy than your average battery.
Theoretically fuel cells can be remarkably efficient, especially when waste heat energy is reemployed, reaching the 85-90% efficiency mark. Even if the kind of fuel cells that might be employed in DSLRs only reached the 50-60% efficiency range, they can still produce more power than a battery. Fuel cells are an area of pretty intense research, and many fuel cells exist that function quite well. High temperature fuel cells have been known to reach as high as 83% efficiency when recycling and reusing heat waste.
Also theoretically, since a fuel cell functions by combining hydrogen and oxygen...they can be "refueled" with water which is then split into hydrogen atoms and oxygen via electrolysis. A well built fuel cell could last for a very long time, and be repeatedly recharged with an external device and clean water.
Now, this is all theory. There have been some applications. Fuel cells have been used in laptops in recent years. Apple is considering powering future macbooks with fuel cells. Fuel cells are being used more frequently in Europe to power all kinds of things. I don't think we will see a rechargeable hydrogen fuel cell any time soon, but I do think that at some point, fuel cells will probably become the standard means of powering larger cameras.