The short answer
At many public chargers, the amount of energy delivered determines a large part of your bill. It is measured in kilowatt-hours and combined with the applicable tariff.
German measurement and calibration law is intended to ensure that:
- a suitable and legally compliant meter is used;
- the measured values are accurate and traceable;
- measurement data cannot be changed unnoticed on its way to the invoice;
- you can verify the readings used for billing.
The German expression eichrechtskonformes Laden therefore describes a form of consumer protection. It does not determine whether a tariff is cheap. It protects the measurement and its traceability.
Coming soon: ChargEV FleX will add its own independent signature and energy verification before automatic billing, complementing the checks already performed by its roaming partners.
Why does EV charging need a special measurement chain?
At a fuel pump, the delivered amount is visible while you are standing beside it. During public EV charging, the measurement and invoice are often separated by both time and distance.
Several systems can sit between them:
- the meter in the charge point;
- the CPO backend;
- a roaming platform;
- the Mobility Service Provider or EMP;
- the final invoice.
The measurement must remain traceable across this chain.
Germany’s Measurement and Calibration Act requires invoices based on measured values to be reasonably easy to verify and requires suitable verification aids where necessary.
What does the meter record?
The electricity meter measures energy during the charging session. Depending on the technical solution, the recorded data can include:
- meter reading at the start;
- meter reading at the end;
- energy delivered;
- start and end time;
- charge-point or meter identifier;
- unique session identifier.
Meters used for commercial billing must meet the applicable legal requirements. These cover measurement accuracy, long-term stability, and protection against unnoticed changes.
What is a signed meter reading?
Many compliant charging systems protect their measurement data with a digital signature.
In simplified terms:
- The charging system creates a record containing meter and session data.
- A protected signing unit signs the record with a private key.
- The corresponding public key can later verify the signature.
- If the signed content is changed, signature verification fails.
OCMF is a common format for such records. Other approved systems can use different formats or verification methods.
A valid signature alone does not prove that every physical measurement is accurate. That also depends on a compliant meter, correct operation, and a trustworthy public key. The signature primarily proves that the signed record has not changed since it was created.
What is a CDR?
CDR stands for Charge Detail Record. It describes a completed charging session and is used for billing and invoicing.
A CDR can contain:
| Component | Example |
|---|---|
| Session identifier | DEMO-CDR-0042 |
| Charge point | EVSE ID and location |
| Period | Start and end time |
| Energy | 18.624 kWh |
| Tariff components | Energy, time, session fee |
| Costs | Calculated amounts by component |
| Signed readings | OCMF or another supported format |
The CDR is normally transferred from the CPO to the EMP through direct or roaming connections.
What will ChargEV FleX verify additionally?
Roaming partners already check charging records and signed proof while transferring them. ChargEV FleX preserves the signed meter data together with the CDR.
The planned ChargEV FleX verification will add its own independent control to this chain. When signed measurement data is available, ChargEV FleX will check questions such as:
- Is the cryptographic signature valid?
- Does the public key belong to the expected charge point or meter?
- Are the start, end, and energy readings internally consistent?
- Does the signed energy match the energy reported in the CDR?
- Can the CDR be linked unambiguously to the session that was started?
After the feature is introduced, automatic billing will be allowed only when the relevant checks pass.
Making verification visible throughout the app
The verification should not end as an invisible backend process. ChargEV FleX intends to carry charging-session traceability through the complete app experience.
After the feature is introduced, customers should be able to see in a clear form:
- whether signed meter data is available for the session;
- whether signature verification passed;
- which energy value appears in the signed record;
- whether it matches the CDR;
- why a session was allowed for billing or held back;
- how to obtain the signed proof for independent verification.
Our aim is to close the gap between technical compliance and understandable customer information. A customer should not need to dispute an invoice or understand specialist transparency software merely to know whether the readings were checked.
This is a deliberate niche for ChargEV FleX: not only enabling charging and payment, but making the bill understandable both before and after the charging session.
What happens when values do not match?
If the signature is invalid or the signed energy does not match the CDR, ChargEV FleX will reject the CDR for automatic billing.
This is designed to prevent an incorrect invoice before it is created. The session is not billed using the unverified value and must be investigated.
For example:
| Value | Energy |
|---|---|
| Signed meter reading | 18.624 kWh |
| Energy stated in the CDR | 21.400 kWh |
| Planned decision | No automatic billing |
The planned energy verification and tariff verification are separate. A correct energy measurement does not prove that the right price was applied. The tariff shown before charging must still be calculated correctly against the verified energy and any other permitted components.
Does a CDR without a signature automatically indicate a problem?
No.
Not every legally approved charging system supplies its evidence in the same way. Some use remotely signed readings, while others rely on a local display or a different method defined by the measuring system’s approval documents.
The absence of an OCPI signed_data field alone does not prove that a charger or invoice is unlawful. The requirements applying to the specific charging system and its approved method are what matter.
Can customers verify the readings independently?
Yes, when the charging session is based on digitally signed readings and the necessary proof data is supplied.
The S.A.F.E. transparency software can verify signed readings. You need:
- the signed measurement record;
- the charge point’s public key;
- the corresponding invoice or charging receipt.
The software shows whether the signature is valid and which readings are contained in the signed record. You can then compare them with the invoice.
The public key should come from a trusted source. Depending on the charging system, it can be found on the meter, through the CPO or EMP, or in data published by the Bundesnetzagentur.
What does German calibration law protect?
| It protects | It does not automatically regulate |
|---|---|
| Accuracy and traceability of measurements | The tariff amount |
| Integrity of transferred meter data | Whether a tariff is inexpensive |
| Verifiability of measurement-based invoices | Charger availability |
| Protection against unnoticed data manipulation | Charging-app quality |
| Use of suitable measuring equipment | Roaming charges and subscriptions |
The European AFIR regulation additionally governs price information before charging. Read our guide to AFIR, EV charging payments, roaming, and prices.
Why is an additional ChargEV check useful?
Checks by several participants create a safety net rather than unnecessary duplication.
- The charge point protects the original readings.
- Roaming partners check data format and plausibility.
- ChargEV FleX will additionally check the signature, key, and match with the CDR itself.
- The customer can later verify the signed proof independently.
Each stage can detect different errors. The planned ChargEV FleX verification will also mean that invoice creation does not depend solely on the result produced by an upstream system.
Frequently asked questions
Is every public charger in Germany compliant?
Charging systems whose measurements are used for billing must meet the applicable legal requirements. Whether a specific charger is operated correctly cannot be determined only from its appearance or an app entry.
Is OCMF legally required?
No. OCMF is a common signed-meter-data format, but it is not the only possible technical solution.
Does a valid signature guarantee a correct invoice?
It does not guarantee the complete invoice amount. It protects the signed measurement data against unnoticed changes. The tariff, taxes, and other components must still be calculated correctly.
What will happen when ChargEV FleX detects a mismatch?
After the feature is introduced, the CDR will not be billed automatically. The reason must be investigated before an invoice can be created from the conflicting values.
Must I verify every invoice myself?
No. Independent verification is an additional right and provides traceability. Roaming partners already check the data today; the additional independent ChargEV FleX verification is coming soon.
In short
German calibration-law-compliant charging ensures that the energy used for your invoice is measured correctly and remains traceable through the billing chain.
Digital signatures make later changes detectable. ChargEV FleX will soon also check those signatures, the trusted meter key, and the match between signed energy and the CDR itself. A mismatching CDR will then not be billed automatically.
This does not automatically make charging cheaper. The additional check is intended to prevent a recognisably incorrect meter value from reaching your invoice unchecked.