Batteries in mains powered AICO alarms

[Jupiter01]

Do the 9v batteries ever get used if there are no power outages?
Is there any advice on when they should be replaced and would there be any visual or audible alert for this?

My interconnected smokes have had the same batteries for around 4.5 years.

 

[CBW]

If batteries are depleting, then usually a bleep iirc once every minute, but check the instructions for recommendations.

 

[secureiam]

The manual gives advice, I believe 10 year lithium's are possible but like most things it depends on usage.