Right now there are numerous devices on my desktop that rely on batteries, including my laptop and my smartphone. For both of these devices, the batteries actually comprise a large amount of their weight and size because only batteries that large and massive can power these devices long enough. That may change soon though, thanks to researchers at the University of Illinois, Urbana-Champaign who have designed the world's most powerful battery that is just millimeters in size.
Batteries store energy by charging ions in their electrolyte, and when you discharge them the ions float over to an electrode and discharge their energy. This process, though effective at storing energy can be quite slow, and many researchers have been looking for ways to improve the speed. In this case the researchers turned to microelectrodes which give the new batteries great energy storage and charge/discharge rates. A cellphone powered by these could feasibly be used to jumpstart your car and then recharge in just seconds.
The next step for these batteries is to find how to best integrate them into other technologies as well as how to mass produce them cheaply. Once that is accomplished this paradigm shift in battery technology could lead to unbelievable battery-lifespans or incredibly small devices.