The standards behind EV charging rarely make headlines, but they decide whether a vehicle, charger and backend can work together without a one-off integration. On 13 July 2026, ISO published Amendment 1 to ISO 15118-20:2022, extending the second-generation vehicle-to-grid communication standard in three important areas:
- an AC Distributed Energy Resource (DER) service for bidirectional AC charging;
- a communication service for the Megawatt Charging System (MCS); and
- a stronger security model for communication between the vehicle and charger.
For charge point operators, this is less about an overnight feature launch and more about removing ambiguity from future infrastructure decisions. The messages needed for AC vehicle-to-grid services now have an international standards home, MCS gains another part of its interoperability stack, and certificate handling becomes a two-sided operational concern.
Here is what changed, what it does not change, and what operators should do next.
First, what does ISO 15118-20 cover?
ISO 15118 describes the high-level conversation between an electric vehicle and the charging equipment. It sits on the cable side of the charger, while OCPP connects the charger to its management platform.
The 2022 edition of Part 20 introduced the second generation of that vehicle-to-charger communication. It supports capabilities such as Plug & Charge, smart energy management and bidirectional power transfer. Amendment 1 does not replace the 2022 standard. It adds and revises requirements within it.
That distinction matters in procurement. A charger advertised as “ISO 15118 ready” may support Part 2, selected Part 20 services, or only the hardware needed for a later software upgrade. Operators need the precise supported edition, services and security profile rather than a single compatibility tick.
1. AC DER gives bidirectional AC a common language
In conventional AC charging, the charger supplies AC power and the vehicle's onboard charger converts it for the battery. Bidirectional AC reverses that conversion when needed, allowing the vehicle to export energy through the same connection.
The new AC DER service standardises the application-layer messages needed to coordinate that exchange. It gives the vehicle and charging equipment a shared way to communicate operating limits, power targets, status and grid-support behaviour.
That can support several related use cases:
- Vehicle-to-grid (V2G): exporting energy to the wider electricity system or responding to a flexibility signal.
- Vehicle-to-home (V2H): using a vehicle battery to support a home or reduce grid demand.
- Vehicle-to-building (V2B): coordinating vehicles with the energy needs of a workplace, depot or other site.
The important step is interoperability. Proprietary AC bidirectional systems can already move energy, but scaling them across vehicle and charger brands requires both sides to interpret the same instructions in the same way. Amendment 1 provides that common messaging layer.
It does not, by itself, make every AC charger bidirectional. The vehicle still needs a bidirectional onboard charger; the charge point and electrical installation must support reverse power flow; and local connection rules, metering, protection, energy contracts and market participation all still apply. The standard tells compatible equipment how to communicate—it does not remove the electrical or commercial work around it.
2. MCS gains its vehicle-to-charger communication service
Megawatt charging is intended for heavy-duty vehicles whose batteries and duty cycles make passenger-car charging speeds impractical. At that power level, interoperability covers much more than the shape of a connector. The system must coordinate power delivery, thermal limits, connection state and safe session control.
Amendment 1 brings the MCS service into ISO 15118-20, linking the high-level vehicle-to-charger conversation with other parts of the emerging MCS stack. These include IEC TS 63379:2026, published on 28 January 2026, which specifies the vehicle connector, inlet and cable assembly for megawatt DC charging at up to 1,500 V DC and 3,000 A.
For fleet and charging operators, this closes an important communication gap. It gives vehicle and charging equipment manufacturers a common protocol target alongside the physical interface and power-delivery requirements.
It is still one layer of the system, not a declaration that every MCS product is mutually interoperable. Operators planning heavy-duty sites should continue to ask for tested combinations of vehicle, charger, cable cooling, firmware and backend—not just compliance with an individual document.
3. Security becomes more explicitly mutual
Bidirectional charging raises the stakes of the vehicle-to-charger connection. The session is no longer only requesting energy; it may authorise power export, communicate grid-related instructions and rely on certificates that connect vehicles, operators and mobility providers.
The amendment strengthens the TLS and certificate model so that the vehicle and charging equipment can each provide a certificate chain the other side can validate. In plain English, trust is no longer framed mainly around the vehicle checking the charger: the charger also needs a reliable way to establish which vehicle it is communicating with.
It also refines certificate-chain selection, certificate-status checking and cryptographic requirements. That is good security design, but it adds operational dependencies:
- trust anchors must be installed and updated correctly;
- certificate expiry and revocation need monitoring;
- vehicle, charger and backend clocks must be reliable;
- failed authentication needs a diagnosable reason and a safe fallback; and
- support teams need to distinguish a certificate problem from a charger or payment fault.
The result is not simply “more certificates”. It is a stronger identity boundary around a connection that can make consequential energy decisions.
How this relates to the EU's 2027 requirement
The timing matters for operators working in the European Union. The amended Alternative Fuels Infrastructure Regulation (AFIR) technical requirements state that public and private AC and DC charging points installed or renovated from 1 January 2027 must comply, for interoperability purposes, with EN ISO 15118-20:2022. For private infrastructure, the text specifically associates the requirement with Mode 3 and Mode 4 charging. The consolidated regulation is available on EUR-Lex.
Amendment 1 gives manufacturers a clearer technical direction before that date, especially for AC bidirectional and heavy-duty charging. However, operators should not treat publication of the amendment as automatic proof of AFIR compliance. The regulation names the European adoption of the 2022 edition, while certification, European adoption of the amendment and the mandatory or optional status of individual services remain questions for suppliers and conformity specialists.
AFIR does not apply directly in Great Britain. UK operators buying hardware for European deployments—or choosing from a hardware market shaped by EU requirements—will still feel its influence.
What recent testing proves—and what it does not
A 2025 research project at the Technical University of Denmark and ElaadNL provides useful evidence that ISO 15118-20 bidirectional communication can work across real equipment. The team reported 11 kW vehicle-to-grid discharge using a Kia EV9 prototype and also tested commercial vehicles and emulators.
There are two important qualifications.
First, the successful EV9 session used the DC bidirectional power transfer service over CCS2, not the new AC DER service. It demonstrates that the broader ISO 15118-20 negotiation and power-reversal model is technically workable, but it is not a field trial of Amendment 1's AC service.
Second, the successful vehicle used prototype software. A production EV9 in the same campaign did not advertise ISO 15118-20 support, while a production Kia EV3 advertised the relevant service but ended the session during negotiation. The researchers also identified certificate management as a remaining deployment barrier.
That is encouraging evidence, not a reason to skip interoperability testing. The protocol and power electronics are progressing; production software, PKI and multi-vendor consistency remain the route from a successful lab session to a dependable service.
What operators should do now
The amendment is a planning signal. It should change the questions asked during procurement and platform design before it changes day-to-day network operations.
- Request service-level compatibility. Ask suppliers which ISO 15118 edition, amendment and services are implemented. “ISO 15118 capable” is not specific enough.
- Check the entire hardware path. For AC bidirectional charging, confirm the vehicle, onboard charger, charge point, metering, protection and site connection can all support reverse power flow.
- Get a firmware roadmap in writing. Hardware described as upgradeable should have a named software release, supported security profile and conformance-testing plan.
- Treat PKI as an operational system. Define ownership for trust stores, renewal, revocation, monitoring and incident diagnosis across charger and backend teams.
- Test real combinations. Validate the actual vehicle models, firmware versions and chargers you intend to operate, including failed handshakes and fallback behaviour.
- Keep the backend ready for richer energy control. Smart charging rules, reliable telemetry and explicit site constraints are prerequisites for useful V2G services, regardless of which power-transfer architecture is used.
- Separate standards readiness from market readiness. Grid connection approval, tariffs, flexibility contracts, battery policy and driver consent need their own workstreams.
The practical takeaway
Amendment 1 moves three important areas from partial or proprietary implementation towards a common international framework. AC bidirectional charging now has a defined application-layer service. MCS has a clearer communication path alongside its high-power hardware specifications. Vehicle-to-charger trust is becoming more robust and more operationally demanding.
The standards layer is settling, but “standardised” is not the same as “widely deployed”. Operators who use this moment to demand precise compatibility claims, build certificate operations and test complete vehicle-to-backend journeys will be better placed to adopt bidirectional AC and megawatt charging without rebuilding their platform later.
Planning for bidirectional charging or a mixed protocol fleet? Explore AmpNexus Smart Charging and OCPP connectivity, or talk to our team about the operational layer behind the hardware.