When I added a 3rd phone line, my ONT was swapped and a GIANT (14" x 24") power supply installed. There are 4 batteries with space for 4 more.
Which leads me to 2 questions:
1) Will I be responsible for replacing all 4 when time claims their life? (I would guess YES)
2) For the VZ techs, will installing 4 more batteries double the run time and/or keep the data service up?
The only good news is that there's a switch to turn the audible alarm on and off!