Won,
You CAN have a backup battery for each screen. Your choice. It doesn't come with you have to order it. If you don't have a battery attached to each screen, and you lose power, then that screen goes dark.
A backup battery on a screen will support the EMS and ADHARS. However, it will NOT support other screens.
Therefore, I have a backup battery on each of my 3 screens.
That answer your question?
