What Is ISO 15118-20? A Complete Guide

If you work in EV charging, you have seen the number on datasheets, tenders and conference slides: ISO 15118-20.

It is usually mentioned in one of three ways — as a compliance requirement, as a feature claim, or as a reason to replace hardware. Rarely is it explained as what it actually is: a communication standard that defines how vehicles and chargers negotiate everything about a charging session, from identity to power direction.

This guide covers what ISO 15118-20 is, how it relates to the rest of the ISO 15118 framework, what it adds over the previous generation, and what it changes for anyone designing, buying or operating charging equipment.

Where ISO 15118-20 sits in the framework

ISO 15118 is officially titled "Road vehicles — Vehicle-to-grid communication interface." It is not one document but a series of parts, each covering a layer of the vehicle-charger communication stack:

Two points worth internalising:

First, ISO 15118-20 is the application layer, not the cable technology. The signals still travel over the charging cable as PLC, defined by the -3 part. What -20 redefines is the conversation itself: the messages, the security model and the services.

Second, ISO 15118-20 does not delete ISO 15118-2. Both generations exist. Devices implement one or the other — and the market is moving toward the second generation, driven by regulation, bidirectional charging and the maturing Plug & Charge ecosystem.

What ISO 15118-20 adds over ISO 15118-2

The second generation is not a patch. It is a redesign of the application layer with the same goal — standardised, secure vehicle-charger communication — and a much larger scope.

Three of these deserve a closer look, because they are what buyers actually ask about.

1. Bidirectional power transfer (BPT)

This is the headline feature. ISO 15118-2 assumed energy flows one way: from the grid to the vehicle. ISO 15118-20 defines the messages for the vehicle to discharge — into a home (V2H), a building (V2B) or the grid (V2G).

That changes what a "charger" is. With BPT support, the charging session includes negotiating discharge power, schedules and grid interaction. For manufacturers, the consequence is structural: a communication module that only implements ISO 15118-2 cannot be upgraded to bidirectional by firmware, because the procedures do not exist in that generation. This is the single most common specification mistake in V2G projects.

2. A modernised security model

ISO 15118-20 moves to TLS 1.3 and extends certificate management. Plug & Charge depends on a working certificate chain — contract certificates, OEM provisioning, a PKI that can issue, renew and revoke. The second generation carries these flows inside the standard more completely, which matters for anyone planning a PnC rollout at fleet or public scale.

3. Finer charge control

The redesigned charge loop gives both sides finer control over power during a session, supporting dynamic schedules and grid-responsive behaviour — the foundation for smart charging and coordinated charging at site level.

The three functions in practice

In datasheets, ISO 15118-20 capability usually appears as three named functions. They answer different questions:

• EIM (External Identification Means) — "Who is charging?" is answered by something outside the session: an RFID card, an app, a backend token. EIM is the fastest to deploy and still the workhorse for public charging.

• PnC (Plug & Charge) — "Who is charging?" is answered by the certificate itself. The driver plugs in; authentication, billing and contract handling happen automatically over the secure channel. No card, no app.

• BPT (V2X) — "Which direction does the power flow?" can be answered with both. V2H backup power, V2G grid services and building-level energy management all run on this.

A charger can implement any combination. Many real deployments start with EIM, add PnC as the PKI ecosystem matures, and treat BPT as the roadmap item that decides which hardware generation to buy.

How a session works, briefly

The sequence below is common to both generations — the details differ, the shape does not:

1. SLAC — the vehicle and charger discover each other electrically on the same cable.

2. SDP — the vehicle finds the charger's communication endpoint.

3. Session setup — the two ends agree on protocol version and supported services.

4. Authentication — EIM or PnC, over an encrypted channel.

5. Charge parameter discovery — capabilities, limits, schedules.

6. Charge loop — power flows, with ongoing adjustment and monitoring.

7. Session stop — clean closure, metering and billing data handed to the operator side.

Note what is not in this sequence: pricing policy, roaming, site-level load balancing, firmware updates. Those belong to the charger-to-cloud link — handled by OCPP, a different protocol on a different link. Confusing the two is the most frequent buyer question in this space.

Who needs ISO 15118-20, and when

Charger manufacturers — if your roadmap includes Plug & Charge, bidirectional charging, or sales into markets with ISO 15118-20 compliance timelines, the second generation is the design target. Retrofit paths exist for AC platforms (see our retrofit guide), but they depend on the communication module, not on firmware wishes.

Fleet and site operators — you do not implement the standard; you specify it. The practical question for a supplier is not "ISO 15118?" but "which generation, and which functions — EIM, PnC, BPT?" A charger specified for ISO 15118-2 today cannot become V2G-capable by update later.

Energy and VPP providers — the aggregated-fleet business model depends on BPT-capable communication end to end. ISO 15118-20 is the layer that makes vehicle participation negotiable and authenticated.

Regulatory direction reinforces this: EU market requirements for public charging infrastructure increasingly reference the second generation, with implementation timelines that make hardware decisions urgent — the logic behind our AFIR compliance checklist.

How to get ready without rebuilding your platform

For a manufacturer with a working AC main controller, the fastest route to ISO 15118-20 is not a new controller. It is an embedded SECC module that carries the second-generation protocol stack and the PLC communication, while the existing controller keeps doing what it does: power switching, metering, protection.

That is the design role of the AUPINS AP-SE-B core board: an SECC PLC communication module for IEC/SAE AC charging equipment, supporting ISO 15118-2 EIM/PnC and ISO 15118-20 EIM/PnC/BPT (V2X) across CCS1, CCS2 and NACS charging interfaces.

• 50mm × 10mm × 30mm footprint, mounted via a 2.0mm-pitch 18-pin single-row header

• Two UART interfaces plus one USB port for configuration, upgrade and diagnostics

• Optional PWM generation, CP detection, PD/PP detection and E-state control

• -40°C to +85°C operating range; 5V (±0.2V) supply, >600mA

• OTA firmware upgrade with log storage and retrieval

The separation matters as much as the capability: the vehicle link and the cloud link stay on different components, which keeps certification scope, firmware ownership and fault isolation clean.

FAQ

When was ISO 15118-20 published?

The second edition of the framework — including Part 20 — was published in 2022, defining the second-generation network and application layer.

Is ISO 15118-20 only for DC fast charging?

No. It applies to AC and DC conductive charging, and its framework is designed with wireless power transfer in scope. For AC charging specifically, it is the generation that brings Plug & Charge and bidirectional capability to wallboxes.

Do I need ISO 15118-20 if I only want Plug & Charge?

Plug & Charge exists in both generations. But if your roadmap includes V2G or V2H, or your target markets reference the second generation for compliance, ISO 15118-20 is the safer specification.

Can an ISO 15118-2 charger be upgraded to ISO 15118-20?

Only if its communication hardware implements the second-generation procedures. A module limited to ISO 15118-2 cannot gain bidirectional power transfer through a firmware update.

Does ISO 15118-20 replace OCPP?

No. ISO 15118-20 is the vehicle-to-charger link; OCPP is the charger-to-cloud link. A commercial charger needs both.

What is the difference between EIM, PnC and BPT?

EIM authenticates by external means (card, app), PnC authenticates by certificate within the session, and BPT enables bidirectional power flow. They are separate functions; a charger may implement any combination.

Conclusion

ISO 15118-20 is the point where EV charging stops being a one-way electrical transaction and becomes a negotiated, authenticated, potentially bidirectional service. For manufacturers, it sets the hardware generation. For operators, it sets what to demand from suppliers. For both, the practical question is no longer whether the second generation matters — it is which functions you need, and whether the hardware you choose today can carry them.

CTA：Evaluating ISO 15118-20 for your AC charger platform? Request the AP-SE-B specification, pin definitions and an evaluation sample from AUPINS.