The section https://icub-tech-iit.github.io/documentation/icub_operating_systems/icubos/bluetooth/#connect-to-the-bcb-board-automatically seems to apply to any icub-head with Bluetooth capabilities, but it actually refers only to iCub 2.5/2.6/2.7 (not iCub 3) that have an actually battery backpack. All other users can safely skip that section.