Why we are not using a button or slider to charge device to just turn page. Very basic device, no wireless communication. You are loading books with usb connection. Only basic formats. Very basic MCU and no operating system Just press the button and change page. Even to adjust font size, you may need to connect it to usb. Once connected to usb, of course we need to charge very small capacitor, but it should be very cheap capacitor so that it can’t hold energy for long. Very minimal, no battery means no carbon footprint of it!