Battery storage commissioning is the structured handover step that proves a home or commercial battery is safe, compliant and working as designed before the installer signs it off, and in 2026 it is no longer an optional extra. MCS recorded around 36,000 certified battery installations in the first half of 2026 alone, and 92% of them went onto homes that already had solar, so a clean commissioning routine is now part of everyday installer practice (MCS, 2026).
Home battery certifications had already jumped 130% year on year across the first half of 2025, so the volume of jobs needing a clean sign-off keeps climbing (UKEM, 2026). Get it right and the client gets a documented, insurable system and you get a defensible record if anything is ever questioned. Get it wrong and you risk a failed inspection, a rejected warranty claim, or a grid connection the network operator never actually approved. This guide walks through the standards, the Distribution Network Operator steps, the tests, a working checklist and the handover pack every UK battery job needs.
Key Takeaways
- MIS 3012 sets the bar: MCS battery installs up to 50kW follow MIS 3012:2025, which demands a documented commissioning procedure and a full handover pack (Energy Stack, 2026).
- Sort the DNO first: a battery inverter over 16A per phase (3.68kW single-phase) needs G99 written acceptance before you commission, not after (Surge, 2026).
- Test every operating mode: BS 7671 protection checks must pass in normal and island modes, with all inverter protection settings recorded.
- PAS 63100 shapes siting: batteries should not sit in lofts or voids, and the standards precedence runs BS 7671, then MIS 3012, then the IET code.
- The paperwork is the deliverable: the handover pack, not just a working battery, is what protects the client and your certification.
What does battery storage commissioning involve?
Commissioning is the process of energising the battery in a controlled sequence, running the required electrical and functional tests, recording the results, and handing the client a complete document pack. It confirms the system matches its design, that protection works in every operating state, and that the grid connection is authorised. It is the line between an installed battery energy storage system (BESS) and a signed-off one.
In practice it blends three things: the electrical verification demanded by BS 7671, the product commissioning routine from the battery and inverter manufacturer, and the scheme paperwork required by MCS. Skipping any one of them leaves a gap that surfaces later, usually during a warranty claim or an audit, when the missing evidence is hardest to recreate.
Which standards govern battery commissioning in 2026?
Four documents set the rules. MIS 3012:2025, effective 1 January 2025, is the MCS installation standard for behind-the-meter systems up to 50kW and covers Electrical Energy Storage System classes 1 to 4 (Energy Stack, 2026). It sits on top of BS 7671, the wiring regulations, with PAS 63100 and the IET code filling in battery-specific safety.
The battery standards at a glance
- MIS 3012:2025: MCS installation and commissioning standard, mandatory for certified battery jobs up to 50kW, sets the handover document list (MCS, 2021).
- BS 7671:2018 + A2:2022, Section 712: the wiring regulations, including battery and solar provisions such as DC-rated protection and lockable isolation (Surge, 2026).
- PAS 63100:2024: fire-safety guidance for batteries in dwellings, used to justify siting decisions (SES, 2024).
- IET Code of Practice for Electrical Energy Storage Systems: the detailed design and install reference the system must meet.
When two documents disagree, follow the order of precedence: the latest BS 7671 first, then the applicable MIS 3012 requirement, then the IET code (Energy Stack, 2026). Record which BS 7671 edition you worked to, because the 2026 transition means both can appear on live jobs for a while.
Do you need G98 or G99 approval before commissioning?
Yes, and the threshold decides your timeline. A battery inverter at or below 16A per phase, roughly 3.68kW single-phase or 11.04kW three-phase, falls under G98: notify the DNO at least 28 days before commissioning and submit the post-commissioning notice within 28 days of energisation (Surge, 2026). Anything above that is G99.
Under G99 you must wait for written acceptance before you energise, and the network operator has up to 45 working days to respond. For a retrofit, add the existing solar inverter's AC output to the battery inverter's: a 3.6kW array plus a 5kW battery inverter totals 8.6kW and tips the whole addition into G99. Plan the application weeks ahead so the connection is approved before your commissioning date, not chasing it afterwards.
Our guides on the G98 notification process, the G99 DNO approval route and the G99 interface relay cover each path in detail.
What electrical tests must you complete at commissioning?
You run the standard BS 7671 verification sequence, then prove it holds in every mode the system can enter. Protection against electric shock, overcurrent and overload must be verified in each intended operating state, including island mode where a backup function is fitted (Energy Stack, 2026). A battery that passes on grid but not in backup is not commissioned.
The DC side needs attention a solar-only install does not. Section 712 of BS 7671 expects DC-rated overcurrent protection, lockable DC isolation and correctly sized DC cabling, with the battery itself listed in the MCS product directory and meeting BS EN IEC 62619 for cell safety (Surge, 2026). Record continuity, insulation resistance, polarity and earth-fault loop values as you go, not from memory afterwards.
How do you commission the battery management system and protection settings?
Set and record the inverter's protection relay values first: under and over voltage, under and over frequency, and rate of change of frequency, matched to the settings declared in your G98 or G99 submission (Surge, 2026). A mismatch between what you submitted and what the inverter actually runs is one of the most common reasons a connection is later queried.
Then verify the battery management system does its job: check it reports state of charge accurately, that cell-level protection trips as specified, and that alarms are wired through to the monitoring platform rather than sitting silent on the unit. Confirm charge and discharge limits, any export limitation, and that the system returns cleanly to normal operation after a simulated fault. A BMS that cannot raise an alarm the client or installer will see is a liability, not a safety feature.
A battery storage commissioning checklist for UK installs
A repeatable battery commissioning checklist keeps jobs consistent and gives you the evidence trail an audit needs. Work through it in order on every install and tick each item against a recorded value, not a glance.
- Pre-energisation: confirm DNO approval is in hand (G98 notified or G99 accepted), isolation points are labelled, and siting meets PAS 63100.
- Visual inspection: check DC and AC terminations, torque settings, cable support, signage and lockable isolators.
- BS 7671 tests: continuity, insulation resistance, polarity, earth-fault loop impedance and RCD operation, recorded on the certificate.
- Protection settings: set and log under/over voltage, under/over frequency and RoCoF to match the DNO submission.
- Functional tests: charge, discharge, export limitation, and island/backup changeover where fitted.
- BMS and monitoring: confirm state-of-charge reporting, alarm routing and remote visibility.
- Handover: compile the document pack, demonstrate shutdown and isolation to the client, and register the MCS certificate.
What handover documents must you give the client?
The handover pack is the real deliverable, and MCS expects a specific set. Energy Stack lists it as the MCS certificate, the BS 7671 electrical certificate and schedules, the G98 acknowledgement or G99/G100 approval records, a system schematic for every operating mode, the commissioning results including backup changeover, product declarations with serial numbers and warranties, fire, shutdown and isolation information, and operating and maintenance instructions (Energy Stack, 2026).
The MCS certificate on its own does not replace these technical records. Give the client a single, labelled pack and keep a copy on file. When a warranty claim or an insurance query lands two years later, the complete commissioning record is what settles it quickly, and its absence is what turns a simple question into a dispute.
Common commissioning mistakes and how to avoid them
The fault we see most often in the field is protection settings left on factory defaults that do not match the DNO submission, which only surfaces when the network operator asks for evidence. Set them deliberately and photograph the screen. The second is a backup function that was never tested in island mode, so the client discovers during the first power cut that the changeover does not work.
A third recurring issue is siting that ignores PAS 63100, with a battery tucked into a loft or an unventilated void because it was the easy run. That decision is hard to defend after a fire-risk assessment and sometimes impossible to insure. Slow down on the parts that are invisible once the cover goes on, because those are the ones nobody can check later.
Turning commissioning into a repeatable process
Battery commissioning rewards consistency. The installers who never scramble for a certificate are the ones who treat the checklist, the tests and the handover pack as one fixed routine rather than a last-hour task. Pair that with proper solar battery sizing at design stage and a clear retrofit storage method, and the commissioning step becomes a formality rather than a firefight.
Keeping the design, the DNO paperwork and the commissioning records in one place helps, and installer platforms such as Reonic are built to hold that trail per job so nothing is recreated from memory at handover. Whatever tool you use, the principle is the same: record as you commission, hand over a complete pack, and the system is genuinely signed off.
Frequently asked questions
Is battery storage commissioning a legal requirement in the UK?
Commissioning itself is how you demonstrate compliance with BS 7671 and, for MCS jobs, MIS 3012. While no single law names the word, the electrical verification, the DNO connection approval and the MCS handover are each required, so in practice a battery cannot be lawfully and compliantly signed off without them (Energy Stack, 2026).
Can I commission a battery before the DNO responds?
Under G98 you can commission after notifying, provided you then submit the post-commissioning notice within 28 days. Under G99 you must wait for written acceptance first, and the DNO has up to 45 working days to reply (Surge, 2026). Energising a G99 system early risks an unapproved and non-compliant connection.
What tests are specific to battery commissioning?
Beyond the usual BS 7671 checks, you must prove protection works in island or backup mode, set and record the inverter protection relay values, and verify the battery management system reports state of charge and routes alarms to monitoring. DC-side protection, lockable isolation and cable sizing under Section 712 also need recorded results.
Where can a home battery be installed under PAS 63100?
PAS 63100:2024 advises against lofts, roof spaces and voids because of fire risk and poor emergency access, though installs can proceed there with suitable safety measures. It also expects adequate ventilation, fire detection that alerts occupants, and a structural check for the battery's weight (SES, 2024).
Does a retrofit battery need a new MCS certificate?
Yes. Adding a battery to an existing solar system needs a revised or supplementary MCS certificate covering both technologies, and the Smart Export Guarantee supplier should be notified. The battery product must appear in the MCS product directory, and the combined inverter capacity decides whether G98 or G99 applies (Surge, 2026).
