Battery Certificate for EVs: Transparency through SoH Diagnostics

In an electric vehicle, the traction battery represents the most valuable single component. It often accounts for between 30 and 50 percent of the total vehicle value. While for a combustion engine, mileage and service history serve as the primary indicators of wear, the valuation of an EV is incomplete without a look into the chemical condition of the battery. A battery certificate closes this information gap. It provides information on how much of the original capacity remains and how healthy the individual cells are.

For private sellers, such a certificate is a decisive selling point. It builds trust and justifies the asking price. Buyers, on the other hand, use the document as protection against expensive follow-up damage. Since manufacturer battery warranties are usually tied to specific SoH thresholds (often 70 percent within eight years), the report provides proof of whether a warranty claim exists or is at risk. DIAVAG offers an independent solution for this that is not tied to the interests of a manufacturer or dealer.

A standard OBD readout, as provided by many simple diagnostic devices, is not sufficient for a reliable battery certificate. DIAVAG relies on the Premium Battery Test as a fixed component of the auf Anfrage premium report. This involves reading deeper parameters via the OBD2 interface and specialized hardware. The focus is on the State-of-Health (SoH), which describes the current remaining capacity relative to the original condition. A value of 92 percent, for example, means the battery can still store 92 percent of its original energy.

In addition to pure capacity, the appraiser analyzes cell balance. If the voltages of the individual cells deviate too strongly from one another, this indicates uneven aging or an emerging defect. Internal resistance and the charging curve are also factored into the assessment. This data is compared against manufacturer-specific target values. The result is a detailed finding that goes far beyond the superficial display on the onboard computer. The measurement is carried out under real conditions on site, without the vehicle needing to be moved to a workshop.

A key differentiator of DIAVAG is its mobility. Traditional inspection organizations such as TÜV or DEKRA usually require the vehicle to be brought to an inspection station. This is time-consuming and often complicated for unregistered vehicles or locations such as ports and garages. DIAVAG reverses this process. The appraiser arrives at the vehicle's location within 24 hours, whether in Hamburg, Berlin, or Munich.

This on-site service saves the customer time and logistics costs. The inspection itself takes less than 15 minutes. During this time, the expert not only conducts the battery test but also documents the visual condition, tread depth, and paint layer thickness using calibrated measuring devices. This efficiency is made possible by a standardized workflow that ensures every report meets the same high quality standard. The completed PDF report is delivered digitally on the same day, which is particularly advantageous for fast transactions in the used car trade.

A battery certificate is only as valuable as the independence and qualification of its creator. DIAVAG appraisers work according to the guidelines of the BVSK (Federal Association of Freelance and Independent Automotive Experts). Every report is also reviewed and signed by a senior inspector. This guarantees a level of technical depth that also holds up before insurance companies or in legal disputes.

CITO GmbH, the company behind the DIAVAG brand, operates as an inspection body according to ISO/IEC 17020 Type A. This is the highest level of independence. Unlike portals that buy vehicles or broker insurance, DIAVAG has no interest in a particular valuation outcome. The report reflects the actual market value and technical condition. In complex situations such as inheritances, divorces, or insurance claims, this neutrality is essential. For specific legal questions, however, a lawyer or notary should always be consulted, with the DIAVAG report serving as a well-founded evidentiary basis.

In the appraisal industry, billing by the hour or based on the object's value is common practice. This often leads to unpredictable costs for the end customer. DIAVAG breaks with this practice and offers clear flat rates. A standard value report for cars, boats, or cargo bikes costs auf Anfrage. For EVs and home storage systems, which require the more elaborate Premium Battery Test, the flat rate is auf Anfrage.

These prices include travel within the regions as well as the entire documentation and provision of the digital report. There are no hidden fees for using the diagnostic hardware or archiving the data. This price transparency is particularly important for private customers who need a reliable basis for calculating their vehicle purchase or sale. Dealers and fleet operators purchasing a larger volume of 50 or more reports per month receive individual terms and can integrate the data directly into their Dealer Management Systems (DMS) via an API.

When comparing providers of battery certificates, clear differences emerge in methodology and scope. Many online services offer only an algorithmic estimate based on age and mileage. Such values are imprecise, as they do not account for individual charging behavior (e.g., frequent fast charging). DIAVAG, by contrast, conducts a physical inspection on site.

This comparison illustrates that DIAVAG bridges the gap between a simple online estimate and an expensive, stationary workshop diagnosis. The coverage of seven asset classes, including home storage systems and boats, is a particular hallmark in the German market.

Regulatory requirements for batteries are steadily increasing. From February 2027, the EU Battery Passport will become mandatory for all new batteries in electric vehicles and industrial applications. This digital passport is intended to contain information on the origin of raw materials, the carbon footprint, and also the current state of health. DIAVAG is already prepared for these requirements today and integrates the necessary data points into its reports.

By using standardized interfaces and tamper-proof documentation - optionally even with a notarial hash on the Polygon blockchain - DIAVAG offers a future-proof solution. Customers who have a battery certificate created today benefit from a data structure that is compatible with upcoming EU standards. This not only increases resale value but also ensures a seamless history of the vehicle's most important component. Data storage takes place in compliance with GDPR on servers within the European Union.

The occasions for a battery certificate are varied. In a lease return, the report serves as protection against unjustified claims by the lessor. When the battery's condition is objectively documented, disputes over alleged excessive wear can be avoided. The battery diagnosis is also essential in the event of an accident. Even if no external damage to the housing is visible, internal cell damage may exist that poses a safety risk.

Another growing area is home storage systems for photovoltaic installations. In real estate transactions, the value of the installed technology is often only estimated. A DIAVAG report including the Premium Battery Test provides an exact value for the storage system here, refining the overall value of the property. A independent certificate also helps substantiate one's own claims in warranty disputes with manufacturers. In every case, the mobile inspection offers the fastest way to arrive at a reliable result.

The DIAVAG appraiser carries a special hardware case optimized for mobile inspection. Its core component is the OBD2 scanner, which communicates with proprietary software. This software allows real-time parameters to be read from the battery management system (BMS). In parallel, digital multimeters are used to validate onboard voltage and other electrical parameters. Visual documentation is carried out via an app that guides the appraiser through a fixed photo catalog to rule out manipulation.

In addition to electronics, mechanical integrity is checked. A paint thickness gauge identifies re-painted areas, which could indicate undisclosed accident damage. Tire tread depth is recorded digitally. All this data flows into the central system, where it is finally evaluated by senior inspection. This hybrid approach of on-site hardware and centralized expert review ensures that human error is minimized and the battery certificate meets the highest quality standards. For independent appraisers, DIAVAG offers this hardware case including a software license for auf Anfrage.