I have a small fuel cell charger that I bought...4, maybe 5 years ago. It also has about the same energy capacity per cartridge, but it's slow releasing that energy. It would be a fantastic solution for UAV's if it were able to discharge at a rate high enough to get some props spinning; I don't think it weighs much more than a 4S 5000 mah. It's very reliable; I've taken it on several medical aid trips into some pretty primitive areas in Central America & Africa to recharge a sat phone. It does that just fine, but it's a slow process...about 5 hours for a full charge.
It's only a matter of time (and I suspect a decreasing amount of that) before we're all looking back on the days when we were only getting 25 minutes flight time from our "high-tech" batteries