Smoke & CO alarms

Firex i5000 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 breaker. Remove the alarm, replace the 9V alkaline backup, remount, restore power, and test.
Orientation	Match +/−
Low battery indicator	Backup low-battery chirp
Notes	Kidde Firex product page: 120V with 9V alkaline battery backup. Listed replacement model: 20SAR.
Access	Tool-free

Hardwired + 9V alkaline backup — confirm alkaline on the label before buying lithium 9V.
When replacing the whole alarm, Kidde points to 20SAR (different mounting/wiring than pre-2009 Firex in some homes).

Last checked 7 October 2026

Firex i5000 uses 1 × 9V.

Buy links go to Amazon (Associates where tagged) or other affiliate programmes when available. They never change the battery answer.

Optional tools for opening, testing or charging — separate from the battery answer.

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Ansmann Energy Check LCD
Quick household cell check (good / low / replace)
Docs Buy on Amazon More tools
ZTS Mini-MBT Multi-Battery Tester
More informative state-of-charge style checks across common formats
Docs Buy on Amazon More tools

Battery tester
Quick good / low / dead check for household cells
Crude check only — does not measure capacity under realistic load.
How to test a battery Buy on Amazon

Buy links are optional and separate from the battery answer.

A fresh 1 × 9V should restore Firex i5000 if the battery was the problem. Work through the checks below before replacing the device.

Check orientation
Confirm the cell is seated correctly: Match +/−
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
Hardwired + 9V alkaline backup — confirm alkaline on the label before buying lithium 9V. When replacing the whole alarm, Kidde points to 20SAR (different mounting/wiring than pre-2009 Firex in some homes).
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.

These checks follow this device’s orientation, battery type, and important notes from the maker.