[timberpro]

I was told by the manufacturer once you disconnect the hard wire remove the alarm from the ceiling then take the battery out. Now this is real important: PUSH DOWN THE RESET BUTTON BEFORE YOU PUT IN THE NEW BATTERY AS THE OLD ALARM STILL HAS A CHARGE FROM THE OLD BATTERY, IT WILL MAKE A SLIGHT NOISE FOR ABOUT 20 SECONDS. Then replace with a new battery and reconnect the wire and put it back in place. Then push the reset button to test the new battery, sometimes it might beep the other smoke dectors when doing this but that is OK.