[IanCal]

Depends on the device. How about this:

An extremely thin tablet that's essentially a touch screen connected to your home computer, aimed for use in the home. Tiny battery, very little computational power & storage, hooked up to your own beefy computer.

Edit - intended for use just in the home. I'd want one, certainly.

[m_mueller]

Too bad screens are using a good chunk of your device's battery. Reducing the radio and computation to close to zero may reduce consumption to 30-50% but it's not an order of magnitude. The batteries are here to stay I'm afraid - until we get some radically different display technology, along the lines of a color, 30 hertz e-ink.

[IanCal]

This was more about having wireless power too (part of the parent comment). You don't need a 10 hour battery on something if you can power it wirelessly.

[kayoone]

if pCell also enables wireless power, youd just need small buffer battery.