I am more concerned about the battery life of the Libre 2 as I am notorious for my phone running out of charge whilst I am out and about. Mostly I manage pretty well with the Libre but there have been times when it has died on me and from what people say, the charge life of the LIbre 2 is pretty short. Can you use it with the alarms off to conserve battery power and then switch them on say overnight when you might benefit most from them? I am currently almost reluctant to swap over to the Libre 2 because I can envisage being caught short for power much more often. During the day I don't always have my phone or the reader on my person, so from what I understand the alarm would be going off that I was out of range and draining the battery unless there is a means of switching it off.....
Are you concerned about the reader, rather than the sensor battery life. I confess I have my phone with me at all times and am not interested in carrying more around so the reader lives in a drawer.
if you are concerned, you can get phone chargers/battery packs which you can carry with you and charge the reader when it is getting low.
Many people charge their phone next to the bed overnight. I guess you can do the same with the reader. I see no reason why it would not last a day.
I have only used the phone app with Libre 2 but you can chose which alarms you want out of high, low and out of range. I have turned the out of range one off. The sensor is attached to me so the only time the out of range alarm would go is if my phone is not near me. So i wouldn’t hear the alarm.
(I guess it may go off if the sensor completely but my experience is that it continues transmitting even when it falls off)
I have not found it drains my phone battery.