Actually, your onto something. Let's say you have a surround speaker that is 100/w/m sensitivity and have a 100Ah Lithium ion battery in there! Could last you a really long time. I mean, let's say your surrounds reached 106dB, you'd have 50hours of time before changing them. Maybe not yet, but, pretty soon, they might have small batteries with really long amp hours and it would be more like changing a watch battery every 5 years.
Donno, but, your point could actually be a step if the technology gets there.