Battery Health in EVs: SoH Measurement and Value Determination

The battery health, technically referred to as the State of Health (SoH), is the central metric for the performance of an electrochemical energy storage device. It is expressed as a percentage and relates the currently usable capacity to the nominal capacity when new. An SoH of 90 percent therefore means that the battery has lost ten percent of its original storage capacity through calendar and cyclic aging.

This value is decisive for preserving the value of an electric vehicle, since the battery is the most expensive individual component of the vehicle. While mechanical parts can often be repaired inexpensively, a significant loss of battery capacity usually leads to a massive loss of value for the entire asset. Appraisers distinguish here between chemical aging, which results from the passage of time and ambient temperatures, and usage-related aging caused by charging cycles and high discharge currents.

A DIAVAG appraisal goes beyond the mere display of the onboard computer. Since vehicle manufacturers often use buffer ranges (gross vs. net capacity), the internal display can obscure the actual state of wear. An independent measurement using calibrated hardware is therefore essential to create a reliable data basis for price negotiations or insurance claims.

Unlike simple diagnostic devices that merely read out the fault memory, DIAVAG uses the Premium Battery Test as the standard for all electric vehicles and home storage systems. This process includes a detailed analysis of cell balance. It checks whether the individual cell modules within the battery pack are charged and discharged evenly. Significant voltage differences between cells indicate incipient defects or uneven aging, which can disproportionately reduce overall range.

Another part of the examination is measuring the internal resistance. Rising internal resistance leads to greater heat generation during charging and driving, which reduces efficiency and accelerates aging. The appraiser also documents the charging curve and compares it with the reference values for the respective vehicle type. This data is collected on site using a mobile hardware case specifically assembled for the requirements of high-voltage diagnostics.

The result of this technical inspection is a BVSK-compliant appraisal. It contains not only the SoH value but also a professional interpretation of the measurement data by a senior inspector. This standardized workflow ensures that the appraisal meets the highest quality standards and serves as an objective basis for transactions. The flat rate for this premium appraisal is auf Anfrages, which represents a necessary safeguard given the investment sums involved in EVs.

The independence of the appraiser is an essential criterion for the legal usability of an appraisal. DIAVAG acts as a neutral party and is not involved in the sale of vehicles, repair services, or insurance brokerage. This strict separation distinguishes the service from platforms that use appraisals merely as a tool to drive down purchase prices. A DIAVAG appraisal serves to protect both parties to the contract.

Compared to classic inspection organizations such as TÜV, DEKRA, or GTÜ, DIAVAG offers specialized depth in battery diagnostics. While conventional roadworthiness tests primarily check traffic safety, the Premium Battery Test focuses on the energetic substance of the vehicle. DIAVAG also covers seven different asset classes, including boats and home storage systems, for which classic inspection bodies often do not offer standardized procedures.

Another differentiator is mobility. The appraiser comes directly to the location of the asset, whether that's the private seller's garage, a dealer's lot, or a harbor for a boat. This saves the customer time-consuming trips to an inspection site. Certification according to ISO/IEC 17020 Type A underscores the highest level of independence as an inspection body, which is particularly important in legal disputes or inheritance conflicts.

In legal contexts, a precise value appraisal is often unavoidable. In cases of inheritance or divorce, the real market value of assets must be determined to enable fair settlements. Since battery health can affect the value of an EV by several thousand euros, a simple estimate based on list price is not sufficient. A BVSK-compliant appraisal from DIAVAG provides the necessary evidentiary strength here.

In the case of an insurance claim as well, for example after an accident or a surge-related fault in a home storage system, detailed condition documentation is required. Insurers often demand proof of the condition prior to the loss event, or confirmation that the high-voltage battery was not damaged by the impact. The use of paint thickness gauges for accident detection combined with battery diagnostics provides a complete picture of the vehicle's condition here.

Should legal questions arise regarding the use of the appraisal or liability, a lawyer or notary should always be consulted. DIAVAG provides the technical factual basis, which is documented in a tamper-proof manner through the signature of a senior inspector and, optionally, a notarial hash on the Polygon blockchain. This technological safeguard ensures that the data cannot be altered unnoticed after creation, which strengthens the document's integrity in court.

Regulatory requirements for battery data transparency are continuously increasing. Starting in February 2027, the EU Battery Passport will become mandatory for all new batteries in electric vehicles and industrial storage systems. This digital passport is intended to contain information about the origin of the raw materials, the carbon footprint, and above all the current condition and expected lifespan. DIAVAG is already prepared for these requirements today and integrates relevant data points into the appraisal structure.

The goal of the EU regulation is to promote the circular economy and strengthen the secondary market for batteries. A transparently documented SoH value makes it easier to decide whether a battery is suitable for a second-life scenario, for example as a stationary power storage unit, or must be sent for recycling. For EV owners, this means that continuous documentation of battery health will become standard practice in the future.

By using standardized workflows and calibrated hardware, DIAVAG ensures that the collected data is compatible with the future requirements of the EU Battery Passport. This secures the long-term relevance of the appraisals and helps fleet operators manage their holdings efficiently and calculate residual values precisely. Data is stored in compliance with GDPR on servers within the European Union.

A growing market for battery diagnostics is the area of PV home storage systems. When selling a property with an existing photovoltaic system, the question of the residual value of the storage system often arises. Since these systems are often operated for ten years or longer, visual condition is of little use in assessing actual remaining capacity. A premium appraisal for auf Anfrages provides clarity here for buyers and sellers.

The diagnosis includes checking the communication interfaces, evaluating the charging cycles, and measuring cell voltages. Home storage systems often develop cell balance problems when the system has not been fully charged for an extended period, or when the battery management system (BMS) software is malfunctioning. The DIAVAG appraiser identifies these weak points on site.

For real estate agents and notaries, this appraisal provides a legally sound basis for structuring purchase contracts. It prevents later warranty claims, since the condition of the storage system at the time of handover is precisely documented. Here too, the independence of the appraiser is key, as there are no sales interests in new devices. The inspection is carried out across manufacturers, for systems from providers such as BYD, Sonnen, Tesla, or LG.

Efficiency is a core promise of the DIAVAG service. An on-site appointment typically takes less than 15 minutes. During this time, the appraiser carries out a standardized workflow that begins with connecting the OBD2 scanner. In parallel, visual documentation is carried out using a specialized app that guides the appraiser through all relevant inspection points. This ensures that no detail is overlooked, from tire tread depth to paint thickness.

The hardware used is housed in a rugged case designed for use under difficult conditions, such as in harbors or on construction sites. In addition to the diagnostic interface, a digital multimeter and a precision paint thickness gauge are part of the standard equipment. These tools are calibrated and regularly maintained to guarantee measurement accuracy. For independent appraisers, DIAVAG offers this hardware case including the software license for auf Anfrages.

Once the on-site data collection is complete, the information is transmitted encrypted to headquarters. There, final review and approval by a senior inspector takes place. The customer receives the finished PDF appraisal by email the same day. This fast process is particularly advantageous for commercial customers such as car dealers or fleet managers, who depend on short standstill times and quick decisions.

DIAVAG offers scalable solutions for professional market participants. Starting at a volume of 50 appraisals per month, individual terms are agreed. A key advantage for dealers is the connection to existing Dealer Management Systems (DMS) via an API interface. This enables seamless integration of appraisal data into the purchasing process and inventory management.

Fleet operators use regular condition assessments to monitor the residual value risk of their electric vehicles. Since the SoH value depends significantly on charging strategy, the appraisals allow conclusions to be drawn about usage patterns. This is particularly relevant for lease returns, in order to objectively justify diminished value and avoid disputes with lessees.

Standardization of appraisals across all locations ensures that a fleet in Hamburg is assessed according to the same criteria as one in Munich or Berlin. This comparability is essential for asset management at large companies. The mobile service also eliminates logistics costs for transporting vehicles to central inspection sites, which significantly reduces the total cost per assessment.

The importance of battery health will continue to grow with the ongoing electrification of mobility and energy supply. A transparent, independent appraisal is no longer a luxury today but an economic necessity. With the flat-rate model of auf Anfrages for standard assets and auf Anfrages for premium assets including battery diagnostics, DIAVAG creates a clear cost structure with no hidden fees.

The combination of mobile availability, technical depth through the Premium Battery Test, and legal protection through BVSK standards sets a new benchmark in the appraisal industry. Whether for private individuals buying a car, for lawyers handling estate matters, or for dealers in their daily business: the objective assessment of battery health creates trust and security in a technologically complex market.

With the planned nationwide rollout in 2026, this service will become available beyond the current regions of Hamburg, Berlin, and Munich. Preparation for the EU Battery Passport also shows that DIAVAG not only serves current needs but actively shapes future regulatory developments. Anyone investing in an EV or a home storage system today should not leave battery health to chance.