the backup is for when the power goes out. I assume you have a land line, they converted it to VOIP which requires the power, unlike the old land line with the low voltage which could run in a black out over the copper lines.
Your back up battery has gone, you don’t need it unless the power goes out and unless when the power goes out you actually still rely on the “land line” which is not longer a land line. So disconnect it and feel safe. they do the backup battery because of the laws for 911.
Alternatively you could use a 12 or 9 volt transformer to plug it in, (check what kind of battery it is) splice wires and directly power the battery connections which will fool the trigger that causes that sound. If the power goes out there wouldn’t be any alarm or phone, cause no power.
And yes Verizon sucks and I have had to deal with this before. Fixed it myself, I don’t have time for idiots on the phone.
Oh, Boy; do we feel STUPID and embarrassed.
This morning my husband woke up with an idea. He looked up under the eaves, about a foot upward from the closet where the Fios box is - and found something.
He had an old weather-watching set, with a monitor that communicates with a component inside to tell us temp, humidity, etc.
It quit working years ago, and we forgot it was there. Today, he found it and took it down - and that’s what was making the noise. It sounds exactly like the Fios box when it needs a new battery - except that it goes off every 3 minutes.
Husband said I shouldn’t tell you all this, because he’ll look like an idiot. But we didn’t even know that thing was still up there.
Peace and quiet for hours now! And we appreciate the time and effort everyone took to try and help us.
(We’ll slink off somewhere now, and succor our collective ego. But in a few hours, I may ask you if it’s ‘legal’ to call the cops on people throwing off fireworks all night...beginning a week before the 4th.)
Thanks again.