Smoke & CO alarms
Firex PAD / AD / ADC battery
1 × 9V alkaline
This device uses more than one power source. Only the user-replaceable cell(s) listed below can be changed.
How to replace it
| How to open | Turn off power at the main panel. Detach the alarm from the plate, unplug the harness if needed, open the battery pocket, replace the 9V on the connector, close the pocket, reconnect, remount, restore power, and test. |
|---|---|
| Orientation | Battery connector fits only one way |
| Low battery indicator | Short beep about once a minute if weak or poorly connected |
| Notes | Classic Firex hardwired photoelectric (PAD) / ionization (AD, ADC) family with 9V backup. Kidde acquired Firex in 2009 and advises replacing aging units with current Kidde models. |
| Access | Tool-free |
Important
- Pre-2009 Firex interconnect often needs a new bracket / KA-F2 adapter when upgrading to modern Kidde alarms.
- While the old unit is still in service, the backup cell is 9V as listed in the Firex/Invensys user guide — not a generic AA guess.
Sources
Helpful for this device
Optional tools for opening, testing or charging — separate from the battery answer.
- Ansmann Energy Check LCD
Quick household cell check (good / low / replace)
- ZTS Mini-MBT Multi-Battery Tester
More informative state-of-charge style checks across common formats
- Battery tester
Quick good / low / dead check for household cells
New battery but still not working?
A fresh 1 × 9V should restore Firex PAD / AD / ADC if the battery was the problem. Work through the checks below before replacing the device.
- Check orientation
Confirm the cell is seated correctly: Battery connector fits only one way
- Check the battery type
This device needs 1 × 9V (alkaline). Rechargeable cells are not supported for this device. Same size does not always mean the same battery.
- Check known model-specific issues
Pre-2009 Firex interconnect often needs a new bracket / KA-F2 adapter when upgrading to modern Kidde alarms. While the old unit is still in service, the backup cell is 9V as listed in the Firex/Invensys user guide — not a generic AA guess.
- Confirm the battery itself
If you have a battery tester or multimeter, check the cell. A low open-circuit voltage often means replace; for rechargeable AA/AAA, a capacity test is more informative than voltage alone.
- Still not responding?
If a correct, fresh battery installed properly does not restore the device, the fault may be elsewhere — the device may need service or replacement.