EV charging protocols and services: communication, access and billing

A charging card can work on one network and be rejected on another, even when the plugs are identical. Charging protocols carry the messages that control power and check access; charging services connect those messages to your account and bill.

Who communicates with whom?

The equipment that supplies electricity to the car is called electric vehicle supply equipment, or EVSE. Its communication with the vehicle establishes how charging can proceed. Separate communication links connect the station to the companies providing the service.

The company operating the charge points is the charge point operator (CPO). The company providing your charging account or card is an e-mobility service provider (eMSP). One company can do both jobs. When you use one provider's account at another operator's station, roaming connects the two services. EVRoaming Foundation — Open Charge Point Interface

Three protocol names appear frequently, each at a different connection:

• ISO 15118 covers digital communication between the vehicle and the charging equipment.
• Open Charge Point Protocol (OCPP) connects the station to its management system, allowing it to report sessions and receive commands.
• Open Charge Point Interface (OCPI) lets operators and service providers exchange information for roaming, either directly or through a hub. ISO 15118-1:2019 — General information and use-case definition Open Charge Alliance — Open Charge Point Protocol EVRoaming Foundation — Open Charge Point Interface

For the route electricity takes through the charging equipment and car, start with EV charging: how the system works. Plug shapes and regional interfaces belong in EV charging connectors and inlets.

How the car and charger agree to charge

Conventional AC charging can use a simple electrical signal on the control-pilot connection to advertise the available current. The car's onboard charger draws within that limit. This lets a wallbox control charging without an ISO 15118 digital session. Argonne National Laboratory — PEV charging response characterization for grid integration (October 2025)

CCS DC charging adds a digital exchange: the car and charger communicate their limits and coordinate the requested voltage and current. CCS implementations can use DIN SPEC 70121 or ISO 15118; a successful CCS session does not by itself establish Plug & Charge support. CharIN — Combined Charging System design guide V7 (2019)

During CCS session setup, the car and charger select a protocol and version they both support. ISO 15118-2 and ISO 15118-20 define different generations of the application protocol; Part 20 includes messages and sequences for bidirectional power transfer. Using that function requires both sides to implement it, along with suitable power hardware. The equipment and installation requirements are covered in Bidirectional EV charging: powering appliances, homes and the grid. CharIN — Combined Charging System design guide V7 (2019) ISO 15118-2:2014 — Network and application protocol requirements ISO 15118-20:2022 — Second-generation network and application requirements

In a simplified CCS DC example, the connected car and charger establish communication, obtain authorisation and exchange charging parameters. They then complete the required safety checks, including an insulation check. During precharge, the charger adjusts its output voltage close to the battery voltage before charging current ramps up. Once charging begins, the car continues requesting current within the available limits. At the end, the systems reduce current and shut down the connection in a controlled sequence. CharIN — Combined Charging System design guide V7 (2019)

The driver's actions can occur in a different order depending on the payment method. Fastned, for example, instructs app users to select the connector before plugging in, and charge-card users to tap their card first. Follow the station or app instructions rather than assuming that plugging in must always be the first step. Fastned — Charging, payment and charge-card billing

Access, price and the final bill

When you tap a charging card, the station reads its identifier and checks, locally or through its management system, whether it may start a session. This permission is authorisation. A card recognised by its provider can still be refused at a station outside that provider's roaming coverage. Open Charge Alliance — OCPP 2.0.1 certification profiles EVRoaming Foundation — Open Charge Point Interface

Authentication establishes trust in an identity or credential, for example through the certificate checks used by Plug & Charge. It is distinct from permission to use a particular station. Payment and settlement handle the financial side: collecting the customer's charge and settling the amounts owed between the companies involved. CharIN — Plug & Charge EVRoaming Foundation — Open Charge Point Interface

Roaming also separates the company supplying the electricity from the company billing you. Fastned states that a customer's charge-card provider may charge a different price from the one Fastned charges that provider, and that the provider sends the bill. The applicable price follows the service you choose to start the session. Fastned — Charging, payment and charge-card billing

With bank-card payment, an amount shown as pending can be a temporary hold rather than the final cost. Fastned reserves funds before charging, then charges the amount due and releases the remainder. The bank controls how quickly the released amount becomes available again. Fastned — Charging, payment and charge-card billing

Behind a roaming session, OCPI can convey the credential for authorisation and return session information and a charge detail record. That record gives the service provider data needed for billing; exchanging it is separate from moving money through a bank or payment processor. EVRoaming Foundation — Open Charge Point Interface

Plug & Charge and Autocharge

With ISO 15118 Plug & Charge, the vehicle presents a digital contract certificate through the charging connection. Trusted certificate authorities issue and sign the certificates used to check the contract credential. These authorities and their supporting systems form a public-key infrastructure (PKI). Once the supported service is set up, the driver can plug in without presenting a separate card or opening an app for each session. CharIN — Plug & Charge

Fastned's Autocharge uses the charging controller's network address, called a MAC address, to identify the vehicle during CCS communication. Fastned links that identifier to the customer's account and payment method. This method does not require the vehicle to present a contract certificate, and it can coexist with Plug & Charge. Fastned — How Autocharge works

Activation requires a compatible vehicle, a Fastned account and a valid payment method. Fastned offers its Autocharge service at its own locations, and its compatibility list can differ from Plug & Charge support. Fastned also asks owners to deactivate Autocharge when transferring the car, so later sessions are not charged to the former owner's account. Fastned — Autocharge compatibility and activation Fastned — How Autocharge works

What OCPP support tells you

OCPP lets the operator's management system receive station status and transaction information, check authorisation and send charging limits. For example, when you start a session through a roaming provider's app, the request can travel through OCPI to the operator's management system. That system can then send a remote-start command to the station over OCPP. EVRoaming Foundation — Open Charge Point Interface Open Charge Alliance — OCPP 2.0.1 certification profiles The scheduling and capacity-control applications are explained in Smart EV charging: schedules, solar power and shared capacity. Open Charge Alliance — Open Charge Point Protocol

If you are choosing a networked wallbox or operating a charging site, check that the station and management service support a common OCPP version. OCPP 1.6 and OCPP 2.0.1 are not compatible protocols. OCPP 2.0.1 adds functions including ISO 15118 support, while OCPP 2.1 extends this to ISO 15118-20 and bidirectional charging. Those are capabilities of the protocol; the installed products must implement the functions being used. Open Charge Alliance — Open Charge Point Protocol

Certification has a scope too. In the OCPP 2.0.1 certification programme, the Core profile is mandatory, while profiles such as Smart Charging and ISO 15118 Support are optional. Check the product's certificate for the relevant profile. A station's OCPP certification alone does not establish that its vehicle connection, contract certificates and account services are ready for Plug & Charge. Open Charge Alliance — OCPP 2.0.1 certification profiles

What happens when a connection fails?

Losing the station's connection to its management system need not interrupt a car already charging. OCPP supports continuing an ongoing transaction and storing messages to send when the connection returns. Starting a new session is a separate question: the station may need an online authorisation it can no longer obtain. Open Charge Alliance — Improving uptime monitoring with OCPP (August 2024)

A card recently accepted at that station may still work if the station has stored its approval in an authorisation cache. An operator can also load a local authorisation list containing accepted cards. Offline acceptance must be supported and enabled, and the relevant card information must still be valid. Open Charge Alliance — Improving uptime monitoring with OCPP (August 2024)

A failed start alone does not identify the broken connection. Possible causes include a vehicle–charger communication fault, a rejected credential or an unavailable management service. A failed link to a roaming partner can also prevent a valid card from being accepted. The station's message, together with the operator's records when you report the fault, helps distinguish these cases. CharIN — Combined Charging System design guide V7 (2019) Open Charge Alliance — Improving uptime monitoring with OCPP (August 2024)

Before relying on a charging service, check the intended station in your provider's app or map and confirm that any automatic-start feature is activated for your car. Keep an accepted alternative payment method available. For physical connection checks, trying another dispenser and planning a backup stop, continue with DC fast charging: station power and planning charging stops.