I found that my battery powered power supply was outputting 4.89V after checking it with a multimeter. Is this not enough to power a pi zero? When I plug the pi into the wall everything is fine. However, when I plug it into the battery powered power supply, it just keeps going to the rainbow screen, the startup screen, and then back to the rainbow screen. Is there anything I should check on the power supply besides the voltage to see why it won't effectively power the pi?
Thanks
The official answer is all models require a 5.1V supply as documented on the RPF site here.
As power needs increase (CPU needs / screen / USB / GPIO) many chargers / supplies will drop the voltage to cope with the increased current demands. This often leads to a reboot loop as CPU requirements during boot are high.
Make sure the max current draw can cope with a fully loaded system (see above linked page) without draining the battery or cooking it and that you have a decent cable between the supply and the Pi.
The voltage should ideally be 5.1 Volts and the recommended current capacity is 1.2 Amps for a Pi Zero.
You should use at least 18AWG cable and no unnecessary connections that can cause voltage drop between the power and the Pi.
https://www.raspberrypi.org/documentation/hardware/raspberrypi/power/README.md
