Although they don't necessarily follow Moore's law, batteries have still gotten smaller and more efficient as the years pass. The current go-to power cell of choice is the lithium-ion battery. It's already quite small as it is, but some scientists think it can get even smaller. How small? Try nanometers.
Researchers at Sandia National Laboratory have built what could be the smallest lithium-ion battery. With anodes consisting of a single nanowire, the battery was so small they had to assemble it under a tunneling electron microscope -- which sees things at the atomic level.
It's not enough to power your iPhone, but the experiment does give us insight on how to make batteries with higher capacities and longer lifespans. It could even lead to power solutions for micro and nanoelectronics.