The question we get every week: do I need a mains-powered smoke alarm, or will a battery-only alarm do? The answer hinges entirely on whether the property is rented out. For owner-occupiers, a BS 5839-6 Grade F alarm with a sealed 10-year battery remains legal and adequate. For every English rental — flat, house, HMO, holiday let — Grade D (mains + battery backup) has been the regulatory baseline since the October 2022 amendment to the Smoke and CO Regulations.
Battery-only is cheaper to install (no wiring) and convenient for owner-occupiers who want to fit alarms themselves. The downside is reliability — flat-battery is still the single largest cause of fire-alarm failure in domestic fires. Mains-powered Grade D eliminates that failure mode entirely: the alarm runs from the lighting circuit and the sealed lithium standby covers any power cut for 72 hours.
Electrician London installs both. For owner-occupiers we fit sealed 10-year battery alarms at £85 per point. For rentals and HMOs we fit Grade D mains + battery at £180 per point — the same per-point rate covers the wiring, the interconnect and the BS 5839-6 certificate.
Why Electrician London
Owner-occupier — Grade F legal
Sealed 10-year battery alarms remain legal in owner-occupied homes. Cheap, fast to fit, no electrician strictly required (though we recommend professional install for interlink).
Rental — Grade D mandatory
Every English rental requires mains-powered Grade D under the 2015 Regulations as amended October 2022. London licensing boroughs audit to this standard.
10-year sealed battery as Grade F
Sealed lithium batteries last the full ten-year head life. No annual battery change, no 3am chirp. Same fire performance as Grade D — just no mains backup.
Upgrade path battery → mains
We routinely convert battery-only homes to Grade D when occupiers become landlords. Same heads can be re-used in some cases; usually a full swap to mains-rated bases.
Battery vs mains install pricing
Per-point pricing for either grade. Survey free with install.
Mains-powered Grade D install
Required in rentals and HMOs
£180 / point
10-year sealed battery (Grade F) install
Owner-occupier — legal, cheap, simple
£85 / point
Battery-to-mains upgrade (existing)
Rewire from lighting circuit, mains base, new head
£180 / point
Interlinked battery (radio-linked)
Owner-occupier multi-storey — Grade F radio-link
£120 / point
Interlinked Grade D mains (3-4 alarms)
Rental baseline for 1-2 bed homes
£550
What's included whichever grade you choose
- Site survey and written LD2 schedule
- Aico, FireAngel or Kidde alarm heads
- BS 5839-6:2019 commissioning test
- Interconnect (wired Grade D, radio Grade F)
- Sealed battery rated for 10-year head life
- BS 5839-6 commissioning certificate
- Minor Works certificate (mains installs only)
- Logbook and install photographs
Frequently asked questions
Is a battery-only alarm legal in my home?
In an owner-occupied home — yes. BS 5839-6 Grade F (battery only) is legal for owner-occupiers and is acceptable to building control on most retrofit work. The legal minimum is one working alarm on every storey used as living accommodation. In a rental property — no, Grade D (mains + battery) is the standard.
What is a 10-year sealed-battery alarm?
A battery-only alarm with a sealed lithium battery that lasts the full ten-year head life. After ten years the entire unit chirps end-of-life and is replaced. Equivalent to Grade F under BS 5839-6 but without the annual battery-change failure mode that plagued older 9V-battery alarms.
My property is owner-occupied today but I might rent it out — what should I fit?
Fit Grade D now. The price difference is modest (£180 vs £85 per point), the install meets the rental standard from day one, and you avoid a second visit later. Many owner-occupier customers choose Grade D for the reliability alone — no flat-battery surprises during a 4am power cut.
Can I interlink battery-only alarms?
Yes — modern Grade F alarms support radio-link modules. Aico Ei3000-series, FireAngel Pro and Kidde Multipro all offer battery-only models with the same Ei3000RF-class radio module as their mains counterparts. Useful for owner-occupier multi-storey homes where running mains cable is impractical.
Why is Grade D required in rentals?
Because flat batteries are the most common cause of non-functional alarms at the moment of fire. Mains power eliminates that single biggest failure mode. The October 2022 amendment to the Smoke and CO Regulations made the rental duty universal across England, and London licensing boroughs treat Grade D interlinked as the audit baseline.
Do you fit battery-only alarms with a certificate?
Yes — every install gets a BS 5839-6 commissioning certificate regardless of grade. The Minor Works Electrical Installation Certificate is only issued for mains installs (it covers the new wiring). Battery-only installs are no-electrical-work jobs but the BS 5839-6 cert still proves design, install and test compliance.
What is the cost difference over ten years?
Battery-only: roughly £85 install plus a £40 replacement at ten years — £125 per point. Mains Grade D: £180 install plus £180 replacement at ten years — £360 per point. The £235 ten-year difference per point buys reliability, interlink-as-standard and the rental compliance baseline.
Can I mix battery and mains in the same property?
We do not recommend it — interlink protocols differ between grades and commissioning is more complex. If you need partial coverage upgrades (e.g. a new kitchen alarm added to an old battery system) we usually advise upgrading the whole property to a single grade. Saves headaches at the next audit.
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