Since we're going through flights of fancy in these threads, another option would be to add a built-in solar panel to your hypothetical e-reader. Expose it to enough light (and you can probably assume the lighting won't be much brighter than a tropical midday sun) and it turns on.
Yes, but then you would both incentive people into placing your device under sunlight and need some of the shortlived kind of capacitors.
It should still be possible to make a solar powered e-reader long-lived, but a replaceable power supply is a good idea even if your device has to last for a couple of years.
A diode bridge (https://en.wikipedia.org/wiki/Diode_bridge) can easily take care of polarity inversions. Voltage is a harder problem.
Since we're going through flights of fancy in these threads, another option would be to add a built-in solar panel to your hypothetical e-reader. Expose it to enough light (and you can probably assume the lighting won't be much brighter than a tropical midday sun) and it turns on.