BS 7671 Chapter 57: the new battery wiring rules, and what to ask your installer

If you are getting quotes for a home battery in the second half of 2026, there is one date worth knowing about: 15 October 2026. From that day, every new domestic battery installation in the UK has to comply with a chapter of the wiring regulations that did not exist eighteen months ago.

This is not a scare story and it does not mean you should rush. It does mean that a quote you receive today may be written against one standard and carried out under another, and that is a fair thing to ask an installer about.

What actually changed

The UK wiring regulations are published as BS 7671. The current edition is BS 7671:2018, and it gets periodically amended. Amendment 4 was published on 15 April 2026 and introduced a new Chapter 57, covering stationary secondary battery installations — which is the formal way of saying “batteries that stay in one place and get recharged”, including the one you are thinking of putting in your garage.

Before Amendment 4, home battery installations were covered by a patchwork: general requirements for electrical installations, manufacturer instructions, and industry guidance that carried no regulatory force. Chapter 57 pulls the specific requirements into the standard itself.

There is a transition period. Installations designed before 15 October 2026 may still be completed to the previous version, but from 15 October 2026 new installations must comply with Amendment 4.

What Chapter 57 covers

Without reproducing the standard — it runs to a fair number of pages and you have to buy it — the areas it addresses are the ones that matter for safety in a domestic setting:

• Where the battery can be located, including proximity to escape routes and habitable rooms
• Ventilation and thermal management, which vary considerably by battery chemistry
• Isolation and emergency disconnection, so the system can be made safe quickly
• Protection against the specific hazards of stored energy — a battery, unlike a solar array, remains live after you disconnect the grid and cover the panels
• Labelling and documentation so anyone working on the installation later knows what they are dealing with

That last point is worth dwelling on. A battery is a source of energy sitting inside your home that cannot simply be switched off. Anyone who works on your electrics for the next decade — an electrician adding a socket, a firefighter, a future homeowner’s surveyor — needs to know it is there and how to isolate it.

Why this matters when you are comparing quotes

Three practical consequences.

First, it separates installers who do batteries from installers who do solar. MCS certifies installers by technology. A company certified for solar PV is not automatically certified for battery storage — they are separate scopes. Chapter 57 sharpens that distinction, because the competence required to install a battery safely is now written down in a place that carries regulatory weight.

Second, it may affect where the battery can go. If an installer quotes for a battery in a particular location and a later assessment finds that location does not meet the new requirements, the job changes. Better to raise that at quotation stage than after a deposit.

Third, it gives you something checkable to ask about. Most of what you will be told during a battery sale is difficult to verify. This is not. Either an installer can talk about Amendment 4 and Chapter 57 or they cannot, and the answer tells you something.

Questions worth asking an installer

Five, and none of them require you to understand the standard yourself:

1. “Are you MCS-certified for battery storage specifically, and what is your certificate number?” You can check it on the MCS website. Certification for solar PV alone is a different scope.
2. “Will this installation comply with BS 7671 Amendment 4, including Chapter 57?” If the work happens after 15 October 2026, the answer needs to be yes.
3. “Where are you proposing to put the battery, and why there?” Location is one of the areas Chapter 57 addresses. A good installer will have a reason, not just a convenient wall.
4. “What documentation will I get when the work is complete?” You should expect an electrical installation certificate, the MCS certificate, and clear labelling of the isolation points.
5. “What happens to the warranty on my existing solar system?” If your inverter is being replaced or reconfigured to work with the battery, this is worth pinning down in writing.

What this does not change

Chapter 57 is a safety standard. It says nothing about whether a battery is a good investment for your house, and neither will we. That depends on your tariff, how much electricity you use and when, whether you export, and what you pay for the system — which is exactly why it takes a site visit and a proper quote rather than a number on a website.

Be wary of anyone who tells you what you will save before they have seen your property. The Advertising Standards Authority has repeatedly ruled against energy companies for savings and grant claims that did not hold up, and a confident figure offered early is a signal about the seller rather than the technology.

The other date in your diary

Separately from the wiring regulations: domestic battery storage currently qualifies for 0% VAT as an energy-saving material, and HMRC has confirmed that relief runs until 31 March 2027, after which the rate returns to 5%.

That is a genuine, dated fact rather than a sales tactic, and it applies to the VAT on the installation — not to anything else about what a battery is worth to you.

Getting quotes? Answer five questions and we will pass your details to up to three MCS-certified battery installers who cover your area. We check certification scope and Amendment 4 compliance before an installer joins the panel — see what we check.

Sources

• BS 7671:2018+A4:2026, published 15 April 2026, mandatory for new installations from 15 October 2026
• MCS — Find an installer, for verifying certification scope
• HMRC VAT Notice 708/6 — the zero rate for energy-saving materials, in force to 31 March 2027