I had a corded phone hooked up for five years and never used it since we never had an outage over a couple hours in that time. If we have an extended outage we may be able to still use our cell phone in an emergency, depending on the extent of the outage.
I am not concerned about the battery cost. Amazon has one for well under $20. I replaced my battery last year after about five years. I am a bit concerned with the replacement procedure. I'm over 80 and it's tough to lie down on the floor to replace the battery. The box is mounted just above the baseboard in our family room. Actually getting down isn't the problem; it's getting up afterwards
I first tried turning off the sound but a day later the alarm started buzzing again.