The military is always looking for new and better ways to power the equipment a soldier has to lug around. I mentioned last year the DARPA initiative to power electronics directly from human body heat and now we're talking storage and how fast you can charge. DARPA awarded industry leader Maxwell Technologies, along with the University of Massachusetts, a contract to develop ultracap energy storage.
Maxwell already makes ultracapacitors; they are like a conventional capacitor but extremely more dense. Per wikipedia instead of having the traditional two plates and a dielectric the two "plates" are separated by a substance rather than empty space. There's still a voltage difference between the two sides, but less physical space is actually needed and therefore more can be crammed into less space. Meaning these end up with a power density of 10 to 100 times your typical battery.
According to Maxwell, soldiers now lug around approximately 60 lbs in batteries or backup batteries. This would enable more power storage than what the soldier is carrying around now, though I wonder that as technology improves and we make better and newer and fancier little devices that this won't just mean the soldier continues to carry around the same weight only now it can power new tools.