It is possible that the battery is not contacting the metal clips inside. See if the can be adjusted out. More likely the detector is not recognizing the voltage of the new battery. You can try removing the detector from the ac power install the battery and reconnecting it to the ac. It should correct the issue.
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It is possible that the battery is not contacting the metal clips inside. See if the can be adjusted out. More likely the detector is not recognizing the voltage of the new battery. You can try removing the detector from the ac power install the battery and reconnecting it to the ac. It should correct the issue.
They don't last forever. If they are more than 7 years old, replace them.