A charging session is a single continuous charging event between one electric vehicle and one charge point connector, from authorization and energy start to the final stop and closing record. In charging infrastructure, the session is the basic unit for metering, billing, roaming settlement, load management and network statistics.
Each session produces a structured record: who charged, where, when, how much energy and at what price. That record travels from the charger to the charge point operator (CPO), often onward to the driver’s e-mobility service provider (eMSP), and finally becomes an invoice line or a payment receipt.
Lifecycle of a charging session
A charging session moves through a defined sequence of states, which are tracked by the charger and reported to the operator’s backend, typically using the Open Charge Point Protocol (OCPP). Understanding the stages helps when diagnosing why a session did not start or why billing looks wrong.
- Identification and authorization: the driver presents an RFID card, uses an app, pays by card terminal or the car identifies itself through Plug & Charge under ISO 15118.
- Connection and handshake: the vehicle and the EVSE agree on limits; for DC charging they exchange voltage, current and battery data.
- Energy transfer: the charger delivers power while meter values are reported at regular intervals.
- Stop: the vehicle reaches its target, the driver ends the session or a fault interrupts it.
- Closing and record: the final meter reading, timestamps and stop reason form the charge detail record (CDR).
The session is not always identical to the time the car is plugged in. A vehicle can remain connected after charging finishes, and many operators distinguish charging time from connection time, because idle occupation blocks the charger for other drivers.
Data recorded for each session
The value of a charging session for operators lies in its data record. A complete record lets the operator bill accurately, settle with roaming partners, prove regulatory compliance and analyze utilization.
| Data field | Example content | Main use |
|---|---|---|
| Session identifier | Unique ID per session | Matching across systems |
| Start and stop timestamps | Date and time, with time zone | Duration and time-based fees |
| Metered energy | Kilowatt-hours delivered | Energy-based pricing |
| Authorization token | RFID ID, contract ID or payment reference | Assigning cost to a customer |
| Location and connector | Station ID, EVSE ID, connector type | Roaming and statistics |
| Tariff and total cost | Applied price elements and sum | Invoicing and receipts |
| Stop reason | Vehicle full, user stop, fault | Diagnostics and uptime analysis |
In many jurisdictions, metered energy must come from a legally calibrated meter, and in Germany and some other countries the record must be cryptographically signed so that drivers can verify the billed energy independently. In roaming, the CDR is exchanged between CPO and eMSP, for example through OCPI.
Types of charging sessions
Sessions differ considerably depending on where and how the vehicle charges. Power level, duration and authorization method together shape the session’s character and its economics.
| Session type | Typical power and duration | Typical authorization |
|---|---|---|
| Home AC charging | 3.7 to 11 kW, several hours | Often none or app-based |
| Workplace or destination AC | 11 to 22 kW, 2 to 8 hours | RFID card or app |
| Public DC fast charging | 50 to 350 kW, 15 to 45 minutes | App, RFID, card terminal or Plug & Charge |
| Ad hoc charging | Any power level | Direct card or QR payment without contract |
| Fleet depot charging | AC or DC, scheduled overnight | Vehicle or fleet ID |
Ad hoc charging has become more important as regulations such as the EU’s AFIR require public chargers above a certain power to accept payment cards without a prior contract. The session then closes with a direct payment rather than a roaming settlement.
Pricing and session management
The session is the unit to which a tariff is applied. Operators can combine several price elements, and the session record must contain enough detail to calculate each one correctly.
- Energy price per kilowatt-hour, the most transparent element.
- Session or start fee, a fixed amount per session.
- Time-based fee, sometimes applied only above a power threshold or during peak hours.
- Idle or blocking fee, charged per minute after the vehicle stops charging but stays connected.
Operators also manage sessions in real time. With smart charging and dynamic load management, the backend can change the power limit of an active session to respect a site’s grid connection, share capacity between several cars or follow electricity prices. A single session at a charging hub may therefore see its power rise and fall several times.
Failed sessions and common problems
From the driver’s perspective, a session either works or fails, but the causes are spread across the vehicle, the charger, the backend and the payment chain. Failed session starts are a key indicator of real-world reliability, sometimes more revealing than charger uptime alone.
| Symptom | Likely cause | Typical fix |
|---|---|---|
| Authorization rejected | Token not synchronized with roaming partner | Retry with app or different method |
| Charging stops after a few seconds | Handshake or communication error | Reconnect cable, restart session |
| Power far below expectation | Cold battery, shared power or high charge level | Precondition battery, choose free charger |
| Session will not end | Backend lost connection to charger | Stop in vehicle or call operator support |
| Incorrect bill | Missing meter values or tariff mismatch | Request the signed session record |
A common misconception is that a session’s average power reflects the charger’s capability. In DC fast charging, the vehicle’s charging curve and battery temperature usually limit power long before the charger does, especially above about 80 percent state of charge.
Stripped to the essentials
A charging session is one visit to a charger, from the moment you start charging until you stop. It is a little like a single fuel stop at a gas station, but with a detailed digital receipt.
During the session, the charger measures how much energy goes into the car, how long it takes and who is paying. At the end, that information becomes the bill. If you use a charging card from one company at a charger owned by another, the session record is what lets the two companies settle the cost between themselves.
Where it is applied
A driver on a long trip stops at a highway charging hub with eight 300 kW chargers. They plug in, and the car authorizes itself automatically through Plug & Charge. The session starts at 12 percent battery and ends 24 minutes later at 80 percent, with 52 kWh recorded by the charger’s calibrated meter.
Because the driver’s contract is with a different provider than the hub operator, the operator sends a charge detail record to that provider through a roaming platform. The provider applies its own tariff and adds the session to the monthly invoice. Meanwhile, the hub operator uses the session’s stop reason and timestamps to track reliability and plan whether additional chargers are needed at peak hours.