SoH Test for EVs: Transparency through Mobile Battery Diagnostics

The State-of-Health (SoH) describes the health status of a battery relative to its original, new condition. In an electric vehicle, the battery often represents up to 40 percent of the total value. A conventional appraisal that only records visual defects and tire tread depth therefore falls short. The SoH test is the only method for objectively assessing the chemical wear of lithium-ion cells. Factors such as charging behavior, the number of fast-charging cycles, and thermal stress leave traces in the cell chemistry that are not visible from the outside.

An SoH value of 95 percent signals excellent condition, while a value of 80 percent already indicates advanced degradation. For the replacement value or the sale price, this difference often amounts to several thousand euros. DIAVAG relies on the Premium Battery Test here, which is included as standard in the 299-euro premium appraisal. This test not only delivers a flat percentage figure but analyzes the actual usable energy in kilowatt-hours (kWh). This is particularly important since manufacturers often use buffer ranges in the software that can distort a superficial look at the dashboard.

The independence of the appraiser plays a central role here. DIAVAG does not sell vehicles and does not carry out repairs. This neutrality is certified under ISO/IEC 17020 Type A and ensures that the result of the SoH test holds up in court, before insurers, or in inheritance matters. In complex legal disputes, you should always consult a lawyer or notary to legally secure the usability of the report.

DIAVAG's mobile service is characterized by a highly efficient workflow. The appraiser comes directly to the vehicle's location, whether that is a private garage, a dealer's lot, or a company parking area. A specialized hardware case is used, containing among other things a calibrated OBD2 scanner and a Premium Battery Test device. The test process begins with reading out the battery management system (BMS). Fault memory entries, charging cycles, and temperature history are recorded here.

The next step is measuring the cell voltages. A key metric is cell balance. If the voltages of the individual cell modules deviate too far from one another, this indicates a defect or uneven aging. The DIAVAG process validates this data through a load test or an analysis of the discharge curve. While conventional testing organizations often only read out basic data, the Premium Battery Test digs deeper into the system architecture. The result is a precise, tamper-proof documentation of the State-of-Health parameters.

The entire on-site inspection typically takes less than 15 minutes. Thanks to standardized processes and the use of digital interfaces, the report is finalized by a senior inspector immediately after the inspection. The customer receives the BVSK-compliant PDF document on the very same day. This time advantage is especially relevant for dealers and fleet operators who depend on fast turnaround times. For commercial customers with a volume of 50 or more appraisals per month, DIAVAG also offers an API connection to existing Dealer Management Systems (DMS).

There are clear differences in the quality and depth of battery diagnostics. Many online services offer estimates based purely on algorithms and statistical values. However, these methods do not account for the individual condition of the hardware on site. A vehicle that was charged exclusively via DC fast charging shows a completely different wear profile than a garage-kept car charged slowly via AC. Without a physical inspection, every figure remains mere speculation.

Testing organizations such as TÜV or DEKRA do offer physical inspections, but they focus primarily on the main roadworthiness inspection (HU) and general traffic safety. A detailed Premium Battery Test that covers cell balance and the exact kWh capacity for EVs and home storage systems is often not part of their standard repertoire. DIAVAG closes this gap through specialized hardware and a focus on value determination. In addition to cars, DIAVAG also covers six further asset classes, including boats, construction machinery, and home storage systems, which is essential for interdisciplinary assessments, such as property sales that include a PV system.

A report is only as valuable as its acceptance by third parties. DIAVAG ensures that all appraisers are qualified according to the guidelines of the BVSK (German Federal Association of Independent Freelance Motor Vehicle Appraisers). This guarantees a high professional standard and adherence to ethical guidelines. In addition, DIAVAG operates as an inspection body under ISO/IEC 17020 Type A. This is the highest level of independence, since the company has no vested interest whatsoever in the condition of the vehicle.

These certifications are especially important when the report is used for legal purposes. In cases of inheritance, divorce, or insurance disputes, courts often require reports that are usable under the German Judicial Remuneration and Compensation Act (JVEG). A simple printout from workshop software is usually not sufficient here. The DIAVAG report is signed by a senior inspector and offers additional protection against tampering through optional notarial hashes on the Polygon blockchain.

A further regulatory aspect is the upcoming EU Battery Passport, which becomes mandatory for all new batteries in the EU starting in February 2027. DIAVAG is already prepared for these requirements today and delivers data structures compatible with future legal requirements. This secures the future viability of the valuation and facilitates cross-border trade in used electric vehicles within the European Union. For specific legal questions regarding usability in ongoing proceedings, you should consult your legal counsel.

The need for a precise SoH test arises in a wide variety of situations. The classic case is a private sale. A seller who can present a certificate showing an SoH of 97 percent justifies a higher price and builds trust. Buyers, on the other hand, use the test to protect themselves against hidden defects. Since manufacturer battery warranties are often tied to certain conditions (e.g., 70 percent capacity after 8 years), the test also serves to check warranty claims shortly before the deadline expires.

In the commercial sector, fleet managers benefit from the mobile inspection. When leased vehicles are returned, an independent report prevents disputes over battery-related depreciation. DIAVAG assesses not only cars here, but also specialized assets such as cargo bikes or e-scooters used in urban delivery fleets. The standardized documentation enables an objective comparison across the entire vehicle fleet.

A growing field is the assessment of home storage systems in real estate transactions. When a house with a photovoltaic system and a battery storage unit is sold, the question of the system's residual value arises. The DIAVAG Premium Battery Test for home storage systems provides the necessary clarity for notaries and buyers. Even in insurance claims, such as after a fire or a flood, the precise determination of the replacement value of the battery is crucial for claims settlement. DIAVAG provides the technical foundation on which insurers can base their decisions.

The quality of an SoH test depends significantly on the hardware used. DIAVAG uses a proprietary system optimized for mobile deployment. The hardware case contains calibrated measuring devices that are regularly checked against industrial standards. In addition to the OBD2 interface, the set includes paint thickness gauges for identifying accident damage, as well as tread depth gauges and digital multimeters. This combination enables a holistic condition assessment of the asset in a single appointment.

For independent appraisers, DIAVAG offers this hardware package, including the associated software, at a list price of auf Anfrages. This allows partners to integrate the standardized DIAVAG workflow into their own portfolio and benefit from the central quality assurance provided by the senior inspectors in Hamburg. The software guides the user step by step through the inspection, ensures the completeness of the photo documentation, and thus prevents errors in on-site data collection.

Data is stored in a GDPR-compliant manner on servers within the European Union. The digital capture of all parameters eliminates error-prone manual transcription of measured values. This is a key factor in the speed of the service. While traditional appraisers often need days to prepare a report, DIAVAG largely automates the creation of the BVSK-compliant report without neglecting technical depth. Every report undergoes a final review by an expert before being sent, to ensure the highest precision.

Transparency begins with pricing. DIAVAG dispenses with complex hourly billing or hidden travel fees within the regions of Hamburg, Berlin, and Munich. For private customers, a fixed price of auf Anfrages applies for standard reports (e.g., combustion-engine cars, boats, or cargo bikes). The premium report, which includes the comprehensive Premium Battery Test for EVs and home storage systems, costs auf Anfrages. This fixed price offers planning certainty for all parties involved.

For car dealerships and fleet operators, individual terms are agreed upon starting at a volume of 50 reports per month. Here, process integration takes center stage. Through the API connection, reports can be requested directly from the Dealer Management System. The mobile appraiser arrives on site within 24 hours, which significantly reduces the standing time of used vehicles. Faster valuation means faster marketing and therefore a higher rate of capital turnover.

The investment in a professional SoH test typically pays for itself as early as the first sales conversation. Avoiding price reductions due to uncertainty about battery condition far exceeds the cost of the report. In addition, DIAVAG's independence reduces liability risk for dealers, since they can rely on an external, certified expert assessment. In a market increasingly driven by transparency and data, the standardized valuation report represents a clear competitive advantage.

The market for electric vehicles is developing rapidly, and with it the demands on diagnostics. The EU Battery Regulation introduces stricter rules for the sustainability and traceability of batteries. The SoH test is thus evolving from an optional service into a regulatory necessity. DIAVAG positions itself as a pioneer here, already capturing today the parameters that will be decisive for future recycling and second-life management of batteries.

An important aspect is the assessment of batteries as stationary storage systems after their use in the vehicle. A precise history of cell stress is essential for this. DIAVAG supports this cycle by providing valid data. The EU Machinery Regulation 2023/1230, which becomes relevant for construction and agricultural machinery starting in January 2027, also underscores the importance of technical safety and documentation. DIAVAG already covers these asset classes today and offers specialized reports for excavators, tractors, and other heavy equipment.

In summary, the SoH test forms the foundation for a fair and transparent used market for electric vehicles. By combining mobile availability, technical depth, and legal certainty, DIAVAG offers a solution that meets the requirements of both private customers and professional market participants alike. Expansion of the service beyond the current regions is planned for 2026 to ensure nationwide coverage of the standardized appraisal service.