>>Thanks, that would be very interesting. The e-ink one should be very light and work on one AAA battery for weeks. :)
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>Maybe I'm thinking of something different than eInk, but I don't think it requires batteries. What I've seen (not in person, only on TV), was paper thin sheet that was more or less an etch-a-sketch. Xerox had been developing it and planned to use it for store signs pretty soon.

There is still a need to apply the electric charge to change the e-ink text and some power to run a little computer if it is eBook screen. In case of eBook device the screen highlight still may be a feature to read without the external lighting (as I do with my current eBook.)