MIT researchers have developed a lithium-ion battery that looks nothing like your standard lithium-ion. Instead of an awkward block, this battery is produced at the molecular level, filling in the tiniest of gaps in your electronics—made possible by its custom balance of electrodes to electrolytes. And the assembly itself requires little manufacturing prowess (money) since chemical reaction drives the structure.
Assuming one could dissipate the heat, nearly 100% of unused case space in any electronic could become battery. And in a world of ever-shrinking processors, design could focus on form and aesthetics with almost no limitations.
Of course, there is still that issue of heat.