Going down the rabbit hole a bit but there has to be some connection to the battery powered backup if it runs on power with normal operation or if it runs on battery only with battery charge. It is unlikely to be a fully self contained system for that reason. A lot of this stuff relies on liklihood of event to get by.
Rumour I read was a massive electrical failure in stormy weather - pilot has zero screens or info, loses wingman and decides its time to jump out before he flies in to something immovable he can't see or sense.