Two meter readings prove every charging session.

Kilowatt and kilowatt hour are easily mixed up. Kilowatt is the speed at which charging happens. Kilowatt hour is the amount that adds up along the way. An example: a wallbox charges for four hours at 11 kW and delivers 44 kWh. At 42 cents per kilowatt hour that session costs 18.48 euros. Billing always follows the amount.

A meter reading behaves like the odometer in a car. It counts upwards and is never reset over the life of the station. The energy charged is the difference between two readings. A meter at 128,400 kWh when charging starts and 128,437 kWh when it ends means 37 kWh went through. Two numbers are enough to document a session.

Those numbers come out of the charging station. Every station holds a meter that measures what passes through the cable. It belongs to the charge point and counts only what that point delivers. The station reports its reading at the start, several times during the session and at the end. The backend takes those readings and works out the difference.

The readings in between earn their keep too. They show progress while the car is still charging. A vehicle plugged in at 22:14 appears on the list of running sessions with the first report. If the link drops mid-session, the last reported reading is the figure you can rely on.

How precisely a meter measures is down to the charging station. For billing charging energy to third parties, German law sets its own requirements for the measuring equipment inside the unit. Those requirements rest on the hardware and its approval. Software reads the values the device supplies.

Every figure on your statement traces back to two meter readings. When a tenant or a driver asks, the start, the end and the difference are all there. The basis for your billing comes from the device that did the charging.