Cherrypicked parial comment: > Reality check, because everyone always gets excited about this: the power density of these devices is on the order of 10 µW/cm^3

Cherrypicked parial comment: > Reality check, because everyone always gets excited about this: the power density of these devices is on the order of 10 µW/cm^3 - about eight orders of magnitude lower than a lithium-ion battery. Technical advances may improve that somewhat, but it will never be competitive with conventional power sources.