Below 50kt you don't really need any of the screens which would be an unnecessary drain on the batteries.
The BAT Bus powers the DC ESS bus which enables you to use VHF1 and FLT Interphone.
Once you come to a stop, it is more important to be able to communicate (ATC, Fire crews, Cabin Crew and Pax) then having all your screens up and running.
REF: FCOM VOL 1 DSC-24-10-30-30 P18/22
Last edited by CEJM; 12th February 2013 at 11:47.