Hi may name is ***** ***** I have been in the home improvement and repair field for 20 years. I will be glad to help you today. The issue is that one of the backup batteries is low and it is warning you to change it. You have to change all of the batteries to solve the issue. It is recommended to change the batteries once a year and to do it when the clocks need to be changed. You will find a slot that pulls out on the side of the smoke alarm to access the battery and they take a 9 volt battery.
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