Comment # 2 on bug 1043432 from H. Zeng

Sorry but I don't how to check the "battery and brightness" while the guest is
in full-screen mode because the host screen is fully covered by the guest
screen.

The status of options in "battery and brightness" including the "Enable Power
Management" are the same before entering and after exiting the full-screen
state. I'm not sure whether this is what you are asking.