Battery Diagnostics for EVs: SoH Measurement and Valuation

The high-voltage battery represents the largest cost factor in an electric vehicle, often accounting for 30 to 50 percent of the total value. Unlike a combustion engine, whose condition can partly be inferred from smoothness of operation or emissions values, the chemical condition of a battery remains invisible to the naked eye. This is where professional battery diagnostics come in. Without valid evidence of the State of Health (SoH), sellers risk significant price reductions, as buyers must assume the worst-case condition.

A certified appraisal creates transparency and trust here. DIAVAG uses a standardized workflow for this assessment that goes beyond a simple fault-memory query. Physical parameters are analyzed that indicate how much of the original capacity is actually still available. This is particularly essential for lease returns or the sale of fleet vehicles, in order to precisely determine residual values and avoid financial losses. The expert's mobile deployment also saves time and logistics costs, as the vehicle does not need to be taken to a specialized workshop.

The Premium Battery Test used by DIAVAG is an in-depth diagnostic procedure specifically developed for the requirements of modern lithium-ion batteries. At the core of the examination is the State of Health (SoH), which describes the remaining total capacity relative to the original condition. An SoH of 90 percent, for example, means the battery can still store nine-tenths of its original energy. But SoH alone is only part of the picture.

The expert also analyzes cell balance. If the voltages of individual cell blocks deviate too much from each other, this indicates uneven aging or an impending defect. The internal resistance of the cells is also assessed, as this significantly affects charging and discharging performance. High internal resistance leads to greater heat generation and reduces the efficiency of the drivetrain. Through the use of calibrated hardware, consisting of OBD2 scanners and digital multimeters, this data is collected in real time and compared against manufacturer-specific target values. The result is an objective snapshot that goes far beyond the often optimistic displays on the onboard computer.

A key advantage of the DIAVAG model is mobility. While classic testing organizations such as TÜV or DEKRA usually require a visit to a stationary inspection facility, the DIAVAG expert comes directly to the asset's location. This can be a private garage, a car dealership yard, or a logistics center. In the regions of Hamburg, Berlin, and Munich, appointments are scheduled within 24 hours, which represents a decisive market advantage, especially for time-critical transactions.

On site, the expert needs less than 15 minutes for the complete inspection. This highly efficient process is made possible by a standardized hardware case containing all the necessary measuring devices. In addition to battery diagnostics, the appointment also includes a paint coating-thickness measurement for accident detection as well as comprehensive photo documentation. Since DIAVAG does not sell repairs or insurance, the assessment remains absolutely neutral. This independence is certified according to ISO/IEC 17020 Type A, representing the highest level of impartiality in the inspection industry. The finished PDF appraisal is delivered the same day and is signed by a senior inspector.

In legal disputes, such as inheritances, divorces, or after an insurance claim, the quality of the appraisal is decisive for its usability. DIAVAG experts work according to the strict guidelines of the BVSK (German Federal Association of Independent and Freelance Vehicle Experts). This guarantees a professionally sound level that can also hold up in court. The reference to the JVEG (Judicial Remuneration and Compensation Act) often serves as a guiding framework for compensation in a court context.

Certification as an inspection body according to ISO/IEC 17020 Type A underscores that DIAVAG has no economic interest whatsoever in the disposal of the vehicle. Unlike purchase portals, which often use appraisals to drive down the price, DIAVAG delivers an objective market value. For complex legal questions, customers should always consult a lawyer or notary to optimally integrate the appraisal results into the legal process. Optionally, DIAVAG offers a notarial hash on the Polygon blockchain to provide tamper-proof evidence of the immutability of the documentation at the time of inspection.

Transparency at DIAVAG begins even before the assignment is placed. The company deliberately avoids complicated hourly billing or hidden travel fees within the regions. For the valuation of electric cars and home storage systems, the premium fixed price of auf Anfrage applies. This price already includes the Premium Battery Test. For standard assets such as passenger cars with combustion engines, boats, or cargo bikes, the fixed price is auf Anfrage.

This price stability allows both private customers and commercial actors to calculate the costs of the valuation precisely. For large customers such as car dealerships or fleet operators who need more than 50 appraisals per month, DIAVAG offers individual terms. Here, integration into existing dealer management systems (DMS) via API is often the focus, in order to automate the inventory-valuation process. The investment in a professional appraisal usually pays for itself already in the first sales conversation, as the objective data situation massively strengthens the seller's negotiating position.

Legal requirements for the transparency of battery data will increase massively in the coming years. From February 2027, the EU Battery Passport will become mandatory for all new batteries in electric vehicles and stationary storage systems. This digital passport is intended to contain information about the origin of raw materials, the carbon footprint, and, of course, the current condition of the battery. DIAVAG is already prepared for these requirements today and delivers data structures compatible with upcoming EU standards.

This regulatory development underscores the importance of regular battery diagnostics. Precise condition data is essential not only for resale but also for recycling and second-life use of batteries. A battery that is no longer powerful enough for use in a vehicle can often still serve as a stationary home storage system for years. DIAVAG's appraisals provide the necessary data basis to make informed decisions about such further usage cycles. In doing so, the company contributes to sustainability and resource efficiency in electromobility.

An often underestimated field of application for battery diagnostics is stationary home storage systems for photovoltaic installations. In real estate transactions, the question of what value the installed technology still holds frequently arises. A PV storage system from manufacturers such as BYD, Sonnen, or Tesla is subject to chemical wear just like a vehicle battery. DIAVAG covers this asset class in the premium segment for auf Anfrage.

The expert checks the capacity and communication of the storage system on site. This is particularly relevant in warranty disputes with installers or manufacturers. If the promised cycle life is not achieved, the BVSK-compliant appraisal serves as objective evidence of the actual condition. Even in the case of an inheritance or divorce, where real estate values must be divided, DIAVAG provides the necessary clarity about the current value of the technical systems. Since many classic appraisers can only evaluate buildings but not complex battery storage systems, DIAVAG closes an important market gap here.

The vehicle valuation market is diverse, but the differences in the depth of battery diagnostics are significant. While large organizations often focus on the main inspection (HU), DIAVAG has specialized in detailed value determination. The following table illustrates the differentiating features:

The combination of mobility and technical depth in the battery check in particular makes DIAVAG the preferred choice for discerning private customers and professional dealers.

For commercial actors, DIAVAG offers far more than just individual appraisals. Car dealerships looking to professionalize their purchasing process for electric vehicles benefit from seamless integration of appraisal data into their existing systems. From a volume of 50 appraisals per month, DIAVAG provides a DMS API. This makes it possible to transfer inspection reports directly into inventory management and publish them on online platforms.

Fleet operators use the mobile appraisals to continuously monitor the condition of their vehicles and determine the optimal time for decommissioning. Since the expert comes to the vehicle, downtime is minimized. In addition, DIAVAG offers self-employed experts a hardware-software package for auf Anfrage. This allows partners to use the proven DIAVAG system to create standardized appraisals of the highest quality in their regions. This ensures nationwide uniform quality, which is of essential importance for cross-regional fleet customers.