You're right about the moving display. British Airways had one of those installed on their L-1011's. If I remember right, it displayed the actual position of the aircraft on the runway. I thought by now the industry would be using GPS for precision landing and taxiing. I've kind of lost touch since I've retired from Lockheed.
The main purpose of aircraft battery is to supply power to the aircraft in emergency situations. On the aircraft that I'm very familiar with, the on board battery is used to start the APU which once on line, supplies power to the aircraft. There is almost no load on the battery unless all other generator power is lost and power is required to operate the aircraft systems.