You know, the big airlines such as a 737, 747 etc., can you turn on the external lights without having ground power, apu or engine ? With only the battery on, can you turn on the nav/steady lights or do you must have AC power in order for external lights to work? (Nav, Wheel well, logo lights)
Many lights - designated backup lights - are 28V DC on airliners (Boeing) - That permits their operation by battery power - Some cabin and cockpit lights are powered by DC as well - Exterior (position lights) are on the DC (battery) bus - Emergency lights such as EXIT lights are powered by essential DC power - 115V AC power, needed either from APU or external power for most lights - Normal cabin lights are all 115V AC - .
Usually they are all DCV and you can turn on all the lights with the battery.
