The MT3608 is a popular boost converter, able to easily step up DC voltages in useful ranges, at an incredibly low cost. Modules can be sourced from eBay for less than $2, built on a PCB, ready to go.

A 3.7V 1100mAh LiPo battery provides power through an MT3608 boost converter module to provide the 5V needed, with the E-Ink display driver further isolated from the power behind a KY-019 5V relay ...