The PiSugar S and PiSugar S Pro can power the Raspberry Pi and Raspberry Pi Zero without hook the SBCs to mains power. Both uninterruptible power supplies can even be recharged through solar power, too.
https://www.notebookcheck.net/The-PiSugar-S-and-PiSugar-S-Pro-bring-battery-power-to-the-Raspberry-Pi-on-the-cheap.550208.0.html