Battery Test for EVs: Procedure, State-of-Health, and Value Determination

The State-of-Health, or SoH, is the decisive metric for the health status of a battery. It describes the remaining capacity relative to the new condition. While a combustion engine is assessed by mileage and maintenance history, in an electric vehicle the battery is the value-determining element. A battery test that merely reads out the fault memory falls short. Significant losses in value can already be present before the system issues an error message.

A precise SoH value makes it possible to estimate the remaining lifespan and actual range of the vehicle. For private sellers, a certified battery test is a strong selling point that justifies the asking price. Buyers, on the other hand, use the appraisal as protection against hidden defects. Since the battery can account for up to 50 percent of the vehicle's value, a deviation in SoH of just a few percentage points leads to significant differences in market value. DIAVAG relies on the Premium Battery Test, which is included as standard in every EV appraisal for auf Anfrage. This test provides an objective data basis that documents actual performance independently of manufacturer specifications.

DIAVAG's Premium Battery Test is based on an in-depth analysis of the battery cells. A key parameter is cell balance. This checks whether the individual cells within the battery pack are charged and discharged evenly. Voltage differences between cells can indicate incipient defects or uneven aging. A conventional OBD2 scan often only shows the value reported by the battery management system (BMS), which can be smoothed by software algorithms.

In addition to cell voltage, the appraiser measures the battery's internal resistance. Rising internal resistance is a clear sign of chemical aging processes and leads to greater heat generation during charging and discharging. This not only reduces efficiency but can also limit fast-charging capability. Measuring the actual capacity in kilowatt-hours (kWh) compared to the factory gross and net capacity rounds out the picture. By using calibrated hardware and standardized test cycles, DIAVAG ensures that results are reproducible and precise. This is especially important for preparing BVSK-compliant appraisals that hold up in legal disputes or insurance claims.

The decision for a battery test often depends on availability and the depth of the inspection. Classic inspection organizations such as TÜV or DEKRA do offer vehicle inspections, but often lack the specialized hardware for an in-depth Premium Battery Test as a standard service across all asset classes. In addition, stationary inspection sites require transporting the vehicle, which costs time and logistical effort.

DIAVAG differentiates itself through independence. Since the company does not buy or repair vehicles, there is no vested interest in artificially devaluing or inflating the asset's value. The appraiser comes to the location of the object, whether that's an underground garage in Hamburg or a depot in Munich. This is a decisive advantage especially for vehicles that are not roadworthy or for stationary home storage systems.

Not only in the mobility sector, but also in real estate, battery diagnostics is playing a growing role. Photovoltaic systems with integrated home storage are standard in modern buildings. When selling a house or in an inheritance case, the question arises as to the value of these systems. A home storage system undergoes aging processes similar to those of a vehicle battery. Cycle stability and remaining storage capacity determine the residual value of the entire energy system.

DIAVAG offers the same high standard for home storage systems as for electric vehicles. The appraiser checks the storage system's communication, the condition of the cells, and the efficiency of the charging electronics on site. This is particularly relevant for warranty claims against the manufacturer. If actual capacity declines significantly faster than contractually guaranteed, the DIAVAG appraisal serves as objective evidence. Here too, the flat rate of auf Anfrage applies, providing planning certainty for property owners and notaries. For complex legal questions in the course of a transaction, however, a specialized lawyer should always be consulted in order to incorporate the appraisal optimally into the contract structure.

An appraisal is only as valuable as its acceptance by third parties. DIAVAG ensures that all appraisers are qualified according to the guidelines of the BVSK (Federal Association of Independent Automotive Appraisers). This guarantees a high level of professional expertise and a methodically sound approach. In addition, DIAVAG acts as an inspection body under ISO/IEC 17020 Type A, representing the highest level of independence.

These standards are essential when the appraisal is to be used for insurers, banks, or courts. Whether for determining the equalization of accrued gains in a divorce, in an inheritance case, or after accident damage to establish the replacement value - a standardized PDF appraisal from DIAVAG provides the necessary legal certainty. Documentation is tamper-proof, optionally supported by a notarial hash on the Polygon blockchain. This ensures that the data cannot be altered afterward. For commercial users such as lawyers or notaries, DIAVAG thus offers a reliable service that meets the requirements of the JVEG (Judicial Remuneration and Compensation Act) in the context of court-admissible appraisals.

Regulatory requirements for batteries are continuously increasing. Starting in February 2027, the EU Battery Passport will become mandatory for all new batteries in electric vehicles and industrial batteries with a capacity over 2 kWh. This digital passport is intended to contain information about the origin of materials, the carbon footprint, and above all the condition and history of the battery. DIAVAG is already prepared for these requirements today and integrates relevant data points into the inspection workflow.

The goal of the EU regulation is to promote the circular economy and strengthen the secondary market for batteries (second life). A battery test is thus becoming a necessary part of lifecycle management rather than an optional service. Through early standardization of testing processes, DIAVAG ensures that the appraisals it produces remain compatible with European requirements in the future as well. This offers investment security in particular for fleet operators and leasing companies, since they can document the condition of their assets seamlessly over the entire term.

Efficiency is a core promise of DIAVAG. The process begins with an online appointment booking, with appointments typically available within 24 hours. The appraiser arrives at the location of the asset at the agreed time. The actual on-site inspection takes less than 15 minutes, since the workflow is optimized through specialized software and preconfigured hardware cases. First, the vehicle or storage system is identified in accordance with the German Road Traffic Licensing Regulations (StVZO and FZV).

The hardware is then connected. While the OBD2 scanner reads out system data, the appraiser conducts a visual inspection and a paint thickness measurement to rule out accident damage. Photo documentation follows a fixed scheme to capture all relevant areas completely. The collected data is transmitted to the cloud in real time, where it is reviewed and finally signed off by a senior inspector. The customer receives the finished PDF appraisal by email the same day. This fast turnaround is a critical success factor especially in commercial settings, such as trade-ins by dealers.

A precise battery test requires more than just a smartphone app. DIAVAG equips its appraisers with a professional hardware case, which is also sold to independent partners for auf Anfrage. At its core is the diagnostic interface, which enables deep communication with the control units of a wide range of manufacturers. This is crucial, since the protocols of Tesla, VW, or Hyundai vary considerably.

In addition, the set includes a digital multimeter for electrical measurements, a paint thickness gauge to check body integrity, and a tread depth gauge for tires. The combination of these tools allows for a holistic assessment of the asset. For the battery test, a special software environment is also integrated that translates raw data into understandable metrics such as SoH. Calibration of the devices ensures that measurement values meet the high requirements of ISO certification. This distinguishes the professional appraiser from hobbyist solutions, which often provide inaccurate or unreliable values.

In the appraisal industry, unclear cost structures and high travel fees are often an obstacle. DIAVAG breaks with this practice through a clear flat-rate model. A standard value appraisal for cars, boats, or cargo bikes costs auf Anfrage. For assets that require complex battery diagnostics, such as EVs or home storage systems, the premium price is auf Anfrage. This price includes all costs, including travel within the regions of Hamburg, Berlin, and Munich.

This transparency is particularly important for private customers who don't want any nasty billing surprises. But the model also offers advantages for professional players. Lawyers can quote costs to their clients immediately, and insurers benefit from a simple calculation basis. There are no hidden fees for preparing the PDF report or archiving the data. Payment is handled easily via common online payment methods, making the entire process from booking to receiving the appraisal seamless.