Battery storage commissioning: what happens and what to ask for

Commissioning is where a well-run project shows itself. A system that is commissioned properly arrives with certificates, completed network-operator forms, recorded settings and people on site who know how to run it. One that is rushed can sit unused, or run with protection settings nobody has checked. This page sets out what commissioning involves for a battery on a business site, what the network operator expects at each size, and the documents to insist on before you sign off the job.

The three parts of commissioning

1. The electrical installation. The installation is inspected and tested to BS 7671, which since Amendment 4:2026 includes a chapter for stationary battery installations (Chapter 57). A new installation is certified with an Electrical Installation Certificate and its schedules of inspections and test results; the IET publishes model forms for BS 7671:2018+A4:2026.
2. The grid connection. Anything that can export to the distribution network is tested to the network operator's requirements under Engineering Recommendation G99: protection settings, export or import limits, and the behaviour the connection agreement relies on. What is tested, and who sees it, depends on the size of the system (below).
3. The battery system itself. The battery management system, power conversion, energy management controls, cooling, and the fire detection or suppression systems are started up and proved against the design. The IET Code of Practice for Electrical Energy Storage Systems covers commissioning alongside design and installation, and the manufacturer will usually set its own start-up procedure as a condition of the warranty.

What the network operator expects, by size

G99 groups generation, including batteries that can export, into four types by registered capacity. The commissioning route follows the type. The figures below come from the Energy Networks Association's Distributed Generation Connection Guide (March 2025).

Types A to C assume a connection below 110 kV. Most behind-the-meter business batteries are Type A or Type B.

Type A: below 1 MW

For most smaller business batteries, commissioning is completed by the installer and reported to the network operator. According to the ENA guide, the tests and checks are those described in section 15 of EREC G99, with the results recorded on Form A.2-4 and in the Installation Document (Annex A.3 of G99), which has one part for the site and one for each power generating module. The Installation Document must reach the network operator within 28 days of the date of commissioning, counting the commissioning day itself, or can be handed over on the day if the operator witnesses the tests. The connection offer itself may say whether the operator will want to witness commissioning, so read it before you book the date.

Types B to D: 1 MW and above

Larger systems are commissioned in stages, with the network operator involved throughout. The ENA guide says the owner must give the operator detailed information about the test scope at least 28 days before the proposed commissioning date, so it can decide whether to witness and inspect. The connection then moves through three notifications: an Energisation Operational Notification before the plant is first connected; an Interim Operational Notification, obtained by submitting a draft Power Generating Module Document, which can limit the maximum output allowed; and a Final Operational Notification once compliance has been demonstrated. Plan the programme around those steps rather than around the delivery date of the battery.

A typical commissioning sequence

The exact order belongs to the installer's method statement, but a commercial battery is usually commissioned in this order:

1. Pre-commissioning checks before anything is energised: terminations, cable routes, earthing, labelling, and the physical installation of the battery and its enclosure against the design.
2. Inspection and testing to BS 7671, recorded on the schedules that support the Electrical Installation Certificate.
3. Safety systems first: fire detection, any suppression, ventilation or cooling, and emergency stops, proved before the battery is put to work.
4. Battery and power conversion start-up, usually to the manufacturer's procedure: battery management system communications, cell monitoring, and charge and discharge at increasing power.
5. Protection and G99 tests: the interface protection, any export or import limitation (G100) and the functions the connection agreement relies on, with the network operator present if it has chosen to witness.
6. Controls and metering: the energy management system's strategy, such as peak shaving or solar self-consumption, proved against live site data, with metering checked so savings can be measured.
7. Handover: documents, training and the start of the maintenance regime.

The handover pack to insist on

Nothing should be signed off until these are in your hands. Ask for the list in the contract, not at the end:

• the Electrical Installation Certificate with its schedules of inspections and test results;
• the completed G99 forms and Installation Document, or the operational notifications for a larger system;
• the protection and control settings, as commissioned;
• as-built drawings and single-line diagram;
• operating and maintenance manuals, including the manufacturer's maintenance intervals;
• warranty registration in your company's name, and any conditions it sets on maintenance;
• commissioning records for the fire detection and any suppression system;
• an outline emergency response plan for the site, and evidence the insurer has seen the final design;
• training for the people who will operate the system, and a named contact for faults.

For a small system installed under MCS, the installer also works to MCS's battery installation standard (MIS 3012), which covers installations up to 50 kW. Most commercial systems are larger than that.

Who is responsible

The installer normally performs the tests, but the obligations do not all sit with the installer. Under G99 the commissioning tests are the owner's obligation, and as a business carrying out a construction project you also have client duties under CDM 2015. Write into the contract who carries out and signs each test, who submits each G99 form, and who attends if the network operator witnesses. The installer checklist includes the questions to ask before you appoint anyone.

Related guides

• How commissioning fits into a containerised BESS installation and an indoor cabinet installation.
• The battery storage fire safety regulations that the design, and therefore the commissioning tests, follow.
• Whether you need planning permission for battery storage before any of this starts.
• What commissioning adds to the cost of a commercial battery installation, and how long the whole programme takes.