Tesla Battery Health Test: Procedure, Principles, and Real-World Results

Many users have already conducted the Tesla battery test themselves, but some still do not fully understand the procedure. This post aims to explain the testing process and underlying principles in detail. At the end, we’ll also compare the results with the degradation analysis provided by Dr.EV.

Tesla provides a built-in feature that allows users to measure battery State of Health (SOH). While manufacturers typically hesitate to disclose this type of internal data, Tesla supports it as part of its philosophy of transparency around battery quality.

The SOH measurement method used by Tesla is not based on estimation but on direct physical calculation of actual battery degradation. This is currently the only method available to users that calculates SOH rather than predicting it. The accuracy of this result depends solely on the precision of the voltage and current sensors, with minimal involvement of modeling errors or external disturbances, making the outcome highly reliable.

Before starting the test, all of the following conditions must be met:

• The vehicle must be in Park (P)

• The battery level must be below 20%

• The vehicle must be connected to the internet

• There should be no scheduled software updates

• No battery or thermal warnings must be active

• The vehicle must be connected to an AC charger

• The AC charger must supply at least 5 kW of power

• The charger must be able to stably deliver the required power upon the vehicle’s request

If any of these conditions are not met, the test may fail. Therefore, it is strongly recommended to verify your charger’s specifications in advance or use a home-installed AC charger rated at 5 kW or higher.

Once the battery health test begins, the status can be monitored through the Tesla app.

At the same time, Dr.EV may show that the battery level drops to 0%.

Even if 0% is shown in Dr.EV, there is still a remaining capacity of approximately 2.4 kWh, so there is no need for concern.

After the test is completed, the SOH of the vehicle battery was measured at 83%. This means the current usable capacity of the battery is 83% of the original design capacity.

The principle behind this test is to measure the voltage at two points during a full discharge and recharge cycle, along with the accumulated charge passed between them. These two points must be selected under stable conditions without external load, and preferably when the battery voltage is close to its Open Circuit Voltage (OCV).

OCV refers to the battery voltage measured when no current is flowing. Since it excludes the influence of internal resistance, it has a well-defined relationship with SOC (State of Charge). By comparing the voltages of the two points against the OCV curve, the change in SOC can be estimated.

In parallel, the amount of charge passed during this interval can be determined by integrating the current. Comparing the change in SOC with the measured charge allows us to infer the total battery capacity.

The inferred capacity can then be compared with the rated capacity to calculate SOH. For example, if the inferred capacity is 10% lower than the original, the SOH would be 90%.

When comparing with Dr.EV, we observed that the SOH values were similar.

However, Dr.EV’s alternative (positive algorithm) method tends to report a slightly higher SOH.

In the alternative method, when the maximum capacity is applied, the results are similar to those from Tesla.

While manufacturers manage the initial capacity according to specifications, it is often difficult to know the exact initial capacity of the actual battery pack installed in the vehicle. To address this uncertainty, Dr.EV manages two reference initial capacities to reflect possible margins of error.

Unfortunately, Tesla's built-in test does not explicitly reveal the degraded capacity value, making it difficult to verify how the initial capacity and degradation adjustment are internally handled. This lack of visibility remains one of the limitations of the official test.