Powering Raspberry Pi Zero with a 3.7V lithium-polymer battery
While you can power a Raspberry Pi through the dedicated USB port, it's not always practical. In certain situations, drawing power from a small and thin lithium-polymer (LiPo) battery makes better sense. This is especially true for projects based on Raspberry Pi Zero, because of the board's modest power requirements. The good news is that powering the Raspberry Pi Zero using a regular 3.7V LiPo battery is cheap and relatively straightforward (some soldering is required, though).
Incorrect wiring or wrong output voltage can damage the Raspberry Pi or the battery. Working with LiPo batteries can be dangerous. MAKE SURE YOU KNOW WHAT YOU'RE DOING, AND PROCEED AT YOUR OWN RISK!