Which Batteries Are Best for Smoke Alarms?
Part of our guide: Rechargeable vs Disposable Batteries: When Each Wins
By the BasketLab team · updated 25 September 2026 · how we rank
Smoke alarms are one of the few household gadgets where getting the battery wrong has consequences a good deal worse than an inconvenience. So let me save you the deliberating: this is not the place for your rechargeables, however green-minded you happen to be feeling. A standard alkaline or a lithium battery, every time. Here's the reasoning.
Most UK smoke alarms take either a 9V block battery or AA cells, and newer sealed units have a 10-year lithium battery that is not replaceable. Open the cover and look, because there is no universal answer. Whichever it takes, use lithium rather than alkaline: it lasts longer, performs in a cold loft and does not leak. Never use rechargeables in a smoke alarm.
What battery does a smoke alarm take?
There is no single answer, and this is the question people most often get wrong. Open the alarm cover and look at what is in there, or check the model number on the back. UK alarms fall into three groups:
| Alarm type | Battery | Replace | Notes |
|---|---|---|---|
| Standard replaceable | 9V block (PP3) | Yearly | The classic type; most older UK alarms |
| Newer replaceable | 2 or 3 x AA | Yearly | Increasingly common on modern units |
| Sealed 10-year | Built-in lithium | Never | Replace the whole alarm at 10 years |
| Mains-powered | 9V or AA backup | Yearly | Backup only; still needs changing |
If your alarm is sealed, there is nothing to buy: the battery lasts the life of the unit and the whole alarm is replaced at ten years. Prising one open to change a cell is not a repair, it is breaking a safety device.
And whatever the alarm takes, every smoke alarm should be replaced ten years after its manufacture date, printed on the back. The sensor degrades whether or not the battery is fresh, and a fresh battery in a fifteen-year-old alarm is not a working alarm.
Why this is the one place to buy premium
We usually argue that own-brand alkalines are fine, and for remotes, clocks and toys they genuinely are. A smoke alarm is the exception, for one specific reason: the battery sits unused for a year or more, so shelf life and leak resistance matter more than raw runtime.
Premium brands guarantee longer storage life and are less prone to leaking, and a leaked cell can destroy the alarm contacts entirely. Spending a couple of pounds more on the one battery in your house that has to work during a fire is the easiest risk-reward call in the home.
Lithium versus alkaline
A 9V lithium battery costs more upfront but typically lasts three to five years in an alarm rather than one, tolerates cold lofts and garages far better, and is much less likely to leak. Over a decade the cost works out similar, with fewer ladder trips.
Alkaline is perfectly safe and cheaper per unit, provided you are disciplined about the annual change. If your alarm is somewhere awkward to reach, lithium is worth it purely for the reduced hassle.
How often to change them, and the chirp
Change replaceable batteries once a year even if the alarm has not complained. A common UK habit is to do it when the clocks change, which makes it easy to remember.
If the alarm chirps every 30 to 60 seconds, that is the low-battery warning: replace it straight away rather than removing the battery. Test every alarm monthly with the test button, and remember that a sealed 10-year alarm cannot be re-batteried, so when it chirps at end of life the whole unit is replaced.
What we would buy
For a standard replaceable alarm: a premium 9V alkaline from a name brand, changed annually, or a 9V lithium if the alarm is high up or in a cold space. For a new install: a sealed 10-year lithium alarm, which removes the annual job entirely and is the direction UK guidance has been moving for years.
Whatever you choose, buy the battery for the alarm separately from your household multipack. Cheap bulk cells are for the TV remote; the alarm gets the good one.
Where alarms should be, and how many you need
Batteries are only half of it. UK guidance is a smoke alarm on every storey of the home, sited on the ceiling in a circulation space such as a hallway or landing, plus a heat alarm in the kitchen rather than a smoke alarm, because cooking sets smoke alarms off and an alarm that gets silenced is worse than none.
Test every alarm monthly using the test button, and vacuum the vents occasionally, since dust is a common cause of both false alarms and failure to trigger. In Scotland and Wales the requirements are stricter than in England and include interlinked alarms, so check your own nation's rules if you rent out or have recently moved.
If you are elderly, deaf or hard of hearing, your local fire service offers a free home fire safety visit in most of the UK and can fit alarms with strobe or vibrating pads. That is a better answer than any battery.
See our picks
Top picks: Best Batteries & Chargers.
Compare: Amazon Basics 20-Pack AA Alkaline High-Performance vs Duracell 2032 Lithium Coin Batteries
Or browse Batteries & Chargers.
Common questions
What battery does a smoke alarm take?
Most UK alarms take either a 9V block (PP3) or two to three AA cells, and newer sealed units have a built-in 10-year lithium battery that cannot be replaced. Open the cover and look, because there is no universal answer.
What are the best AA batteries for smoke detectors?
Lithium AA cells. They last several times longer than alkaline in a low-drain device, work reliably in a cold loft or hallway, and do not leak, which is the failure that destroys alarms. This is the one household device where paying for lithium is clearly worth it.
Can I use rechargeable batteries in a smoke alarm?
No. Rechargeables self-discharge steadily and give a lower voltage, so an alarm can fail without warning between checks. Use a lithium or good alkaline primary cell.
How often should you change a smoke alarm battery?
Once a year for replaceable types, and immediately if it chirps. A common habit is to change them on the same date each year so it is not left to memory. Sealed 10-year alarms are never changed; the whole unit is replaced.
Why does my smoke alarm keep chirping?
A single chirp every 30 to 60 seconds almost always means a low battery. If a new battery does not stop it, the alarm may be at the end of its life, the vents may be dusty, or the unit may need resetting. Check the manufacture date on the back.
How long do smoke alarms last?
Ten years from the manufacture date printed on the back, regardless of battery condition. The sensor degrades over time, so a fresh battery in a fifteen-year-old alarm is not a working alarm.
How many smoke alarms do I need?
UK guidance is one on every storey, on the ceiling in a hallway or landing, plus a heat alarm rather than a smoke alarm in the kitchen. Scotland and Wales have stricter rules including interlinked alarms.
Do smoke alarm batteries drain faster in the cold?
Alkaline cells lose capacity noticeably in the cold, which matters for alarms in lofts, garages and unheated hallways. Lithium performs far better at low temperatures, which is another reason it suits this job.