Which battery does a smoke or CO alarm take?
The correct battery is the one listed by the alarm's manufacturer. It is printed on the back of the alarm, inside the battery door, or in the manual. Common types are 9V, AA and, in some units, 3V lithium cells such as CR123A.
Before you buy
- Sealed 10-year alarms have a non-replaceable battery. When they reach end of life, replace the whole alarm.
- Hardwired alarms often have a backup battery. Replace it with the type printed on the unit.
- Rechargeable batteries: many alarm makers say not to use them. Follow your manual.
Testing and replacement
Test alarms monthly with the test button. A chirp usually means a low battery, though on some units it signals end of life. NFPA guidance calls for replacing smoke alarms 10 years after the manufacture date printed on the unit; CO alarms have their own replacement date on the label.
Batteries in our catalog
- Olight AA 2100mAh 1.2V Nickel Metal Hydride (NiMH) Low Self Discharge Button Top Battery - Box of 8 — $28.00
- Panasonic Alkaline Plus Power AA Batteries - 48 Count Box — $31.99
- Panasonic Alkaline Plus Power AAA Batteries - 48 Count Box — $37.99
- Panasonic CR123A (12PK) 1550mAh 3V Lithium (LiMnO2) Button Top Photo Batteries - 12 Piece Retail Card — $45.99
- Panasonic CR123A (6PK) 1550mAh 3V Lithium (LiMnO2) Button Top Photo Batteries - 6 Piece Retail Card — $34.99
- Panasonic Eneloop K-KJS1MCA-2BA AA 2100mAh 1.2V Low Self Discharge Nickel Metal Hydride (NiMH) Button Top Batteries with D Cell Spacers - 2 Pack Retai — $26.99
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Related categories: Smoke & CO Alarms · Batteries. General information only; follow the equipment maker's instructions and local codes. Updated 2026-11-14.