Always awesome to watch and see things appear after a long coding spree where you read the hex values like you're interpreting the matrix fluently. Amazing work!
@AsahiLinux and whoever might be interested: as I understand it for GNOME users there is a ‘Battery threshold’ extension, but it hard-codes BAT0 so I made https://github.com/francku/gnome-shell-extension-battery-threshold/pull/11 which should hopefully make it work properly.