Home battery fire safety: cell chemistry, siting and PAS 63100

Home batteries are safe when they are well made, properly installed and sensibly sited. But if a lithium battery does catch fire, it is hard to put out. This guide covers what the UK guidance says, why cell chemistry matters and what to sort out with your installer and insurer.

Why battery fires are different

A faulty lithium-ion cell can overheat and set off a chain reaction known as thermal runaway. The Netherlands Institute for Public Safety (NIPV) notes this can start from around 80 °C, with a risk of explosion and toxic gases, and that burning batteries are very hard or impossible to extinguish because of how they are built ¹. Prevention is therefore everything: good cells, a reliable battery management system (BMS) and a sensible location.

Cell chemistry: LFP or NMC

The home battery market has largely moved to LFP. For one model in our database the datasheet doesn’t state the chemistry. You can see the choice in the weight, too: the median across our database is about 11.6 kg per kWh. If you’re looking at an older or second-hand system, always check the chemistry.

LFP is not a guarantee, though. The BMS, cell quality and installation matter at least as much.

PAS 63100 and the IET Code of Practice

PAS 63100:2024 is a BSI specification for protecting battery energy storage systems in homes against fire. It covers requirements such as battery and fault management and installation locations ³, including whether a battery can go in a loft ⁴.

Its status is worth understanding ⁴:

• PAS 63100 has no current standing in UK regulations such as Building Regulations.
• It is not directly referenced in the MCS battery storage installation standard (MIS 3012).
• The IET Code of Practice for Electrical Energy Storage Systems (3rd edition) recommends that PAS 63100 “should be considered” generally and “should be used” for decisions about battery location.

In practice, a competent installer will use PAS 63100 when deciding where your battery goes. Ask how they have applied it, and get the reasoning in writing if they propose an unusual location.

Where to put a battery

The Energy Saving Trust notes that batteries can be installed in garages, on external walls or in utility rooms, depending on the product ⁵. Public safety bodies abroad give similar advice: not in living spaces such as bedrooms, not in escape routes, not under stairs and not next to combustible materials, with a technical room, outbuilding or a garage (protected against vehicle impact) as better options ².

Better

• utility room, plant room or outbuilding;
• garage, protected from the car;
• external wall, with a suitable IP rating.

Avoid

• bedrooms and living rooms;
• hallways, stairs and other escape routes;
• next to boilers, heaters or stored combustibles;
• anywhere your installer can’t justify under PAS 63100.

A smoke alarm in the room with the battery is a sensible extra, especially in a garage or utility room you don’t use often.

Outdoors or unheated: IP rating and temperature

If the battery will go outside or in an unheated space, check its IP rating and minimum operating temperature. In our database:

• 24 models are rated IP65 or IP66, 12 IP55 and 2 only IP20 (indoor use only).
• The minimum operating temperature is −20 °C for 20 models, −10 °C for 16 and 0 °C for 2.

Avoid direct sun and heat, which speed up ageing and raise the risk.

Installation

• Use an MCS-certified installer; the Energy Saving Trust recommends getting at least three quotes ⁵.
• Ask for handover documents showing the circuit, protection devices and settings.
• Keep the battery and inverter software up to date.
• A clear label at the consumer unit showing that a battery is present, and where, helps firefighters.

Insurance

Tell your home insurer before installation. Ask whether the battery is covered under buildings or contents insurance, whether they have conditions about location or installer certification, and get the answer in writing. Keep the invoice, MCS certificate and installation records.

If something goes wrong

If you smell something acrid, see smoke or hear hissing or popping: leave the room, close the door and call 999. Don’t try to put out a burning battery yourself.

In short

1. Prefer LFP with clear safety documentation.
2. Site it outside bedrooms, living rooms and escape routes, following PAS 63100.
3. Use an MCS-certified installer.
4. Tell your insurer, and your DNO via the installer – see AC vs DC-coupled batteries.

How long a battery lasts and what the warranty covers is explained in home battery lifespan and warranties.