The basic requirement is that the electric standby has its own separate power supply to provide for fhe statutory operating time.
The sim implementation is a bit theatrical in that the device works fine for around 30 minutes whereupon all goes black and all present have a chuckle before we try again with far more effort directed to getting VMC or on the ground before blackness descends once more.
Once the backup power is exhausted it is a case of "all over, Red Rover" unless you are VMC or on the ground. Any function remaining is problematic and will depend on the system design.