Well, smaller batteries would seem to be the most obvious answer. With that in mind, researchers at the University of Maryland have succeeded in creating a tiny battery that incorporates even smaller structures, known as nanopores.
The battery is made from a postage stamp-sized sheet of ceramic material, with an array of millions of microscopic holes going through it – these are the nanopores, and they're each about one eighty-thousandth the width of a human hair.
Each one contains an electrolyte solution and has a nanotube electrode at either end, those electrodes serving as an anode and cathode. This setup allows each of the nanopores to act as a sort of minuscule sub-battery – all of which are connected in parallel – storing and discharging energy together.