Constructer
Junior Member level 3
Makes only sense if you replace the relays by 9V type. Otherwise you need to drop down the voltage with series resistor, same overall power consumption as if supplying the relays by 5V linear regulator. Or use 9 to 5V switched mode regulator.
The 9v supply powers the Reference voltage IC, and the dedicated 5v regulator for Arduino.
Operating the coils from 9v Battery should be fine, power consumption was not the consideration.
Relays JQC-3FF-05:
https://www.futurlec.com/Datasheet/Relays/JQC-3FF.pdf#page=1&zoom=auto,-32,842