The page stays put after the power stops
Most dedicated e-readers use electronic paper, a display designed to hold an image without constantly refreshing it. In a common version, tiny capsules contain light and dark charged particles suspended in fluid. Electrical signals move selected particles toward the front of the screen, forming letters against a pale background.
Once the particles are in position, they remain there. The screen does not need to keep sending power to every letter to preserve the page, unlike a typical phone or tablet display, which continually drives its pixels to produce a lit image. This persistent state is called bistability: the display can keep either of two visual states—light or dark—without continuous power.
What uses the battery instead
Power is needed when the image changes. Turning a page, opening a menu, or refreshing the screen sends new electrical signals to rearrange the particles. The e-reader also draws energy for tasks such as processing a book, connecting to wireless networks, and running its operating system.
A built-in light, when switched on, is another continuing drain. Unlike a phone screen that shines light outward, many e-readers use LEDs along the edge to illuminate the display from the front. That makes reading possible in the dark, but the longer and brighter the light stays on, the more battery it uses.
So a page can remain visible for weeks because the display spends energy changing the image, not holding it. A reader that is left open on a page uses far less power than one that is constantly paging, syncing, or lit brightly.
