From what I can see the only system that is supplied directly from the Hot Battery Bus in normal flight, is the Wireless control units for the emergency lights.
Does it need to be kept fully charged in flight?
I would say yes. If you are in such dire straights that any systems need power from your main battery, you need every amp for as long as possible.
Brakes are ALL electric. No hydraulic back up. Just multiple independent power sources.
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