Gather the correct replacement battery
Check the smoke detector type and battery compartment
Turn off power to the detector if it is hardwired
Remove the detector from its mounting bracket if needed
Open the battery compartment
Remove the old battery
Insert the new battery with the correct polarity
Close the battery compartment
Reattach the detector if it was removed
Restore power if it is hardwired
Press the test button to confirm proper operation
Replace the detector if it does not work after battery replacement