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?


2 Answers 2


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.

  • Yup, it was the wire! Just needed a higher gauge. Thank you!! Apr 29, 2021 at 3:00

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.


  • Just got a new short, higher gauge micro usb cable and it works like a charm. Thank you! Apr 29, 2021 at 2:59

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