The author already powers the Pi directly from the battery, and they switch off the inverter when it's not used. (see the image diagram and one of their respons

The author already powers the Pi directly from the battery, and they switch off the inverter when it's not used. (see the image diagram and one of their responses in the comments) Anyway, you wouldn't need a 'load' port in the charge controller, just put it in parallel with the battery.