I don't think we'll get more battery life. Manufacturers will use the extra energy density, when it becomes available, to make smaller devices, and the average dumbphone is back to 1 week life and smartphone back to 1 day life.

It has happened with laptops, and it has happened with phones before. Whenever a new generation of chips that use dramatically less power, or a new generation of higher capacity batteries become available, you get at most one model with decent batterylife, after that they realize they can save costs by making the battery smaller, and can make the device smaller by having a smaller battery. People think the new small model is "cute" or "sleek", and soon everyone thinks the old one is "huge" and "clunky", and (implicitly) demand manufacturers to cripple the batteries to get smaller devices