Detailed instructions at link (see posts below for RPI 4)

  • Switch OFF USB/LAN IC: If you don’t need any USB devices switching off the USB BUS chip off can save more than 100mA of power (!!!)
  • Turn OFF HDMI: it is possible to switch off HDMI output by a simple command. This can save you up to 30mA
  • Throttle CPU:
    we can down clock the core by changing some parameters in the /boot/config.txt file (power savings likely neglible)
  • Disable Wi-Fi & Bluetooth in /boot/config.txt dtoverlay=pi3-disable-wifi dtoverlay=pi3-disable-bt
  • Disable on-board LEDs in /boot/config.txt: dtparam=act_led_trigger=none dtparam=act_led_activelow=on power saving around 30mA.