Stationary Battery Storage and BS 7671 Amendment 4: A Guide for Solar and EV Installers

For years, electricians installing battery energy storage systems (BESS) in the UK have been working without a dedicated chapter in BS 7671 to guide them. Industry best practice, MCS standards, PAS 63100, and manufacturer guidance filled the gap — but the national wiring regulations themselves said nothing specific about batteries.

That has changed. When the IET and BSI published BS 7671:2018+A4:2026 on 15 April 2026, they introduced new Chapter 57: Stationary Secondary Battery Installations — the first time BS 7671 has had dedicated regulations for battery storage. From 15 October 2026, when the previous edition is formally withdrawn, every new battery installation in the UK must comply with it.

If you install solar PV with battery storage, standalone home battery systems, commercial BESS, or EV chargers with V2H or V2G functionality, this article covers what the new chapter requires and what you need to do to stay compliant.

Why did BS 7671 need a dedicated battery chapter?

Battery storage technology has moved from niche to mainstream in the space of a few years. Home battery units paired with solar PV — think Tesla Powerwall, GivEnergy, SolarEdge — are now a standard part of many domestic solar installations. Commercial and industrial BESS is being deployed at scale for demand management and grid services. And EV charging is increasingly integrated with battery storage systems capable of feeding power back into the building or the grid.

Throughout this growth period, BS 7671 offered no specific guidance. Electricians were designing and installing battery systems using general rules that were never written with batteries in mind. Chapter 57 changes that, giving the industry a formal, consistent baseline for safety that reflects how batteries actually behave — including the unique risks they present.

What does Chapter 57 cover?

Chapter 57 applies to battery systems intended for permanent installation where their main purpose is to store and supply electrical power. That covers:

• Domestic battery storage, including systems paired with solar PV
• Commercial energy storage
• Grid-connected battery arrays
• Systems used for off-peak storage, backup power, and UPS functions

It does not apply to batteries used solely as a power source within equipment (such as a UPS unit supplied as a self-contained appliance), or to traction batteries in vehicles.

The chapter addresses six core areas:

1. Location restrictions

This is the change most installers will feel immediately. Chapter 57 introduces specific restrictions on where battery systems can be sited, informed by fire safety evidence and aligned with the existing PAS 63100:2024 standard.

Lofts are now formally prohibited. This is the most significant practical restriction. Lofts present multiple fire safety problems for lithium-ion batteries: extreme ambient temperatures in summer, poor or no ventilation, combustible building materials in close proximity, difficult access for maintenance or emergency response, and the fact that a fire in the loft is directly above sleeping areas. The ban on loft installations formalises what responsible installers were already avoiding — but it now carries regulatory weight.

Other prohibited or restricted locations include:

• Escape routes, corridors, and stairwells
• Cellars and basements with no direct external access
• Within 1 metre of windows, doors, or ventilation openings (for external installations)
• Within 2 metres of stored flammable materials or fuel tanks

Acceptable locations include garages, utility rooms with appropriate fire separation, dedicated plant rooms, and external wall-mounted or ground-mounted installations in a suitable weatherproof enclosure. The key requirement across all acceptable locations is that the system must be accessible for maintenance and inspection, and must not compromise means of escape in the event of fire.

2. Thermal runaway mitigation

Thermal runaway is the condition most relevant to battery fire risk. It occurs when a battery cell overheats, causing a self-sustaining exothermic reaction that can rapidly spread to adjacent cells and result in fire or explosion. The risk is most associated with lithium-ion chemistries, though it can occur across battery types.

Chapter 57 introduces specific requirements to detect and mitigate thermal runaway risk. These include requirements around battery management systems, temperature monitoring, automatic disconnection in the event of fault conditions, and — for domestic installations — smoke or heat detection in the space where the battery is housed. PAS 63100:2024 is explicitly referenced for domestic installations (Regulation 570.6.7.203), meaning compliance with Chapter 57 and PAS 63100 go hand in hand for domestic BESS work.

For non-domestic installations, the location and fire protection measures must be based on a formal fire risk assessment for the premises.

3. Ventilation requirements

Chapter 57 sets requirements for ventilation of battery enclosures. Adequate ventilation serves two purposes: it limits heat build-up during normal operation (which extends battery life and reduces fault risk), and it provides a pathway for gases to escape if thermal runaway begins — reducing pressure build-up and the risk of explosion.

Requirements vary depending on battery chemistry and enclosure type. Vented lead-acid batteries have different ventilation needs from sealed lithium-ion systems, and the regulations reflect this. If you are installing in an internal room, you will need to consider ventilation as part of your design — not as an afterthought.

4. Safe isolation procedures

Chapter 57 introduces specific isolation requirements for battery systems that reflect the unique challenge batteries present: unlike most other electrical sources, a battery cannot simply be switched off at the supply. A battery that is not correctly isolated will continue to present a live DC voltage even after the main AC supply is disconnected.

The new requirements standardise how battery systems are isolated from both the solar array (or other charging source) and the AC grid or load. This is relevant for your method statements, your labelling, and your safety briefings for other trades who may work near a battery installation after you have left site.

5. Disconnection arrangements and overcurrent protection

The chapter sets out requirements for disconnection devices and overcurrent protection that are specific to battery installations. This includes requirements for protective devices capable of handling two-way energy flow — relevant for bidirectional systems used in vehicle-to-home (V2H) and vehicle-to-grid (V2G) applications. Standard AC overcurrent devices are not always rated for DC or bidirectional operation; the new regulations make the selection criteria explicit.

6. Labelling and documentation

Chapter 57 introduces labelling requirements for battery installations, including the system's nominal voltage, capacity, chemistry, and isolation points. Documentation requirements include recording the installation details on the Electrical Installation Certificate. This is a practical change that affects your standard certification paperwork.

What about EV chargers?

Amendment 4 also tightens earthing and protection requirements for Electric Vehicle Supply Equipment (EVSE) more broadly — not just integrated battery-EV systems. If you install EV chargers as a standalone product, you should review your current installation methods and equipment selections against the updated requirements in the Orange Book.

For EV chargers with V2H or V2G capability — which act as a bidirectional energy flow point between the vehicle battery and the building or grid — the new battery chapter is directly relevant. The protective devices and disconnection arrangements for such systems need to handle two-way current flow, and Amendment 4 makes this explicit for the first time.

How does Chapter 57 relate to PAS 63100?

PAS 63100:2024 (Protection Against Fire of Battery Energy Storage Systems) already applies to domestic BESS installations and sets requirements for fire separation, smoke detection, and siting. It is a publicly available specification published by the BSI.

Chapter 57 does not replace PAS 63100 — it works alongside it. For domestic installations, Regulation 570.6.7.203 in Chapter 57 explicitly requires compliance with PAS 63100. In practice, if you are already working to PAS 63100 for domestic battery work, much of the location and fire protection content will be familiar. What Chapter 57 adds is the electrical design and installation requirements — isolation, disconnection, protection devices, ventilation design — that PAS 63100 does not cover in detail.

For non-domestic installations, PAS 63100 does not apply directly, but Chapter 57 requires that a fire risk assessment informs the location and fire protection measures.

Does this apply to existing installations?

No. Amendment 4 is not retrospective. Existing installations that complied with the regulations in force at the time of installation do not need to be upgraded. However, if you carry out any addition or alteration to an existing battery installation after 15 October 2026, that work must comply with Chapter 57.

There is one important practical implication: if you are asked to inspect or certify a battery installation that was installed before October 2026 and does not comply with the new chapter — for example, a battery installed in a loft under a previous installer — you should note any observed departures from the current edition on the EICR. You cannot force a retrospective upgrade, but you are not in a position to certify such an installation as satisfactory against current standards.

What do you need to do before October 2026?

1. Read Chapter 57 in the Orange Book. There is no substitute for reading the actual regulation. Buy the Orange Book from the IET Bookshop from 15 April 2026. If you install battery storage, Chapter 57 is essential reading — not optional.

2. Review your current method statements. Your standard approach to battery installation almost certainly needs updating. Location selection, isolation procedures, labelling, and documentation all need to reflect the new requirements.

3. Review upcoming and in-progress projects. For any battery project scheduled for completion after 15 October 2026, you should be designing and installing to Chapter 57 now — even during the transition period, it is good practice and reduces the risk of non-compliant installations.

4. Update your certification templates. The new documentation and labelling requirements mean your EIC templates and completion documentation need to capture additional information about battery systems.

5. Brief your team. If you work with apprentices, labourers, or subcontractors who work around battery installations, the isolation and labelling requirements need to be communicated clearly.

6. Take Amendment 4 update training. If you hold an 18th Edition qualification, a focused update course covering Chapter 57 and the other Amendment 4 changes is the most efficient way to get up to speed formally. This matters for your competent person scheme membership and your CPD records.

Chapter 57

Chapter 57 is not a bureaucratic formality. It was introduced because battery installations present genuine safety risks — particularly thermal runaway and fire — that previous regulations were not designed to address. The loft installation ban, the ventilation requirements, the isolation procedures, and the alignment with PAS 63100 all exist because real fires in battery installations have highlighted the consequences of getting this wrong.

If you install solar PV with battery storage, standalone BESS, or EV systems with integrated battery functionality, Chapter 57 directly governs your work from October 2026. Getting trained, reading the regulation, and updating your methods now means you will be ahead of the deadline — not scrambling to catch up when it arrives.

Virtual College's 18th Edition Amendment 4 training covers Chapter 57 and all other key changes in a flexible online format. Whether you need a full qualification or a focused update course, you can start today.