Since the Pi zero 2 w can be powered off a power bank.

A 20,000 mah power bank easily gives over 24 Hours of use !

Only drawing 1 watt of power with everything booted up and idle and that's with the usb to etherent adapter connected as well.

You can download / upgrade by running the following on the Raspberry Pi (either SSH into the Pi or on the actual Pi) :-

wget -qO- https://raw.githubusercontent.com/diddy-boy/mini-pi-media-server/main/install.sh | bash