What's preventing us from putting fuel cells in laptops and tablets soon? Is it just that today's fuel cell designs are physically bulky? Are we near theoretica

What's preventing us from putting fuel cells in laptops and tablets soon? Is it just that today's fuel cell designs are physically bulky? Are we near theoretical limits on fuel cell miniaturization or is there still lots of headroom? What's the safest way to store the fuel? Are there too many downsides to making the fuel cell air-breathing (as opposed to the danger of storing oxygen)? http://en.wikipedia.org/wiki/Fuel_cell http://en.wikipedia.org/wiki/Fuel_cell Wikipedia says that fuel cells are typically "stacked" (placed in series) since each one only makes 0.7v, but if a new tablet is designed to save space by using only a single 0.7v cell and upregulating the voltage with a boost regulator, won't the total efficiency even with regulator losses still be far above li-ion?