Notification for power failure

And my last sentence states that requirement :stuck_out_tongue_winking_eye:

I do it a different way with a script running on my FirstNet Router that uses the I/O port on router connected to a wall transformer/relay. When relay trips the I/O port script sends SMS from modem.
And it has a 21 hour battery currently:
Battery Backed-Up 14 V3 cams and Internet Communications