Maybe a science fiction writer will invent an electronic reader that doesn't depend on electricity.
Perhaps future readers will use batteries that are trickle-charged by solar cells, for those of us who suffer power failures from time-to-time. Many years ago I had a Casio calculator that opened a bit like a reader in a cover. It had a panel of solar cells on the left-hand side that was connected to the calculator and battery on the right, via a flexible ribbon cable. A novel idea at the time, but it was rather heavy. Nowadays lighter thin film and flexible polymer solar cells are available.