Batteries.

As Olaf pointed out in the comments on my post about exoskeletons, the problem is power. In fact that’s a big problem with all our present technology so someone must be researching it. Just a little google brings up some seriously SFnal research. Here’s a few samples:

MIT scientists have harnessed the construction talents of tiny viruses to build ultra-small "nanowire" structures for use in very thin lithium-ion batteries. By manipulating a few genes inside these viruses, the team was able to coax the organisms to grow and self-assemble into a functional electronic device.

The LEES ultracapacitor has the capacity to overcome this energy limitation by using vertically aligned, single-wall carbon nanotubes -- one thirty-thousandth the diameter of a human hair and 100,000 times as long as they are wide.

Like turning straw into gold, MIT researchers have transformed a relatively common material, lithium iron phosphate, into one with handsome potential for the next generation of rechargeable batteries in electric cars and other devices. Among other advantages, the material could make such batteries cheaper and safer.

In March, PNNL engineers reached the first major milestone in development when they demonstrated a full-size, advanced design fuel processor that converts methanol into hydrogen. Because hydrogen wouldn't need to be stored or carried, the fuel processor would reduce the weight and risk associated with portable power systems.

The researchers believe their breakthrough shows promise that graphene (a form of carbon) could eventually double the capacity of existing ultracapacitors, which are manufactured using an entirely different form of carbon.

A team from the Laboratory’s Chemistry and Materials Science Directorate and the Center for Microtechnology Engineering has been working for the past several years on a tiny device that can process minute amounts of fuel, such as hydrogen from methanol and water, to in turn feed a miniature fuel cell for powering unattended sensor systems and eventually consumer electronics.

Note to self: read more science articles and less about politics and you might turn into an optimist.