They probably had a use for the scrapped slam ball scene. There may have been plans to show the lights go from green to yellow to red and have a comical scene where Marty falls from a wall or ceiling. Since we only see the green LEDs lit up they most definitely were to signify charge. Having them all lit up for the 2011 and 2016 releases were probably just so they looked cooler.Maybe give we never see yellow or red illuminated on screen.