Beeping backup battery

[Chimp2]

I replaced the backup battery for my Fios router and it continues to beep. I pressed the silence alarm button multiple times but it always starts beeping again. Can anyone help?

[Edg1]

Is the Battery LED on the Back up unit off? If so it might be something else beeping. My sister complained to about this exact same issue and I went over and it was her smoke alarm.