Khaberni - When buying a used car that runs on a gasoline or diesel engine, one usually relies on certain factors to assess the condition of the car before purchasing, such as reading the odometer, checking for any oil leaks, reviewing the condition of the timing belt, and engine noises can indicate the car's condition. However, with electric models, there are no rattling valves or worn clutches, and the battery is the most critical point of inspection.
But the problem is that one cannot determine the safety of the battery in a used electric car merely by looking at it or listening to it, and this is where the importance of what is known as the battery's State of Health (SoH) check comes in, which is the main measure for assessing the condition of the most expensive component in the car.
The electric car expert at the ADAC German automobile club, Matthias Vogt, said: "The abbreviation SoH refers to the battery's state, and is usually explained in percentage terms."
He added: "The battery's State of Health (SoH) describes the current battery capacity percentage compared to its original capacity. When the value is 100%, it means that the battery can store the same amount of energy it stored on the first day of its operation. If this value decreases, it means a reduction in the distance that can be covered with a battery charge."
There are two main measures that play a crucial role in determining the battery's condition, namely: battery capacity, which is the stored energy, and the internal resistance of the battery, which indicates how much energy loss occurs inside the battery.
However, there are no standard criteria or specific measurement procedures to determine the battery's state of health (SoH), and therefore it is not possible to compare the battery state value with the WLTP driving range.
Vogt explained: "Each car manufacturing company defines this value differently in its warranty terms, complicating things for the end customer."
There are currently main methods for determining the battery's state; in the energy analysis, the amount of energy that can be extracted is measured, and in this case, the battery is fully charged, then the car is driven until the battery is nearly empty, after which the company calculates the SoH value through algorithms.
Another method involves measuring the internal resistance of the battery, which requires a short acceleration. If the resistance is high, it indicates a greater voltage drop and heat generation, which leads to a decrease in the usable capacity of the battery.
In addition, some car manufacturing companies provide the possibility of directly extrapolating the battery's state through the Battery Management System (BMS), and the German expert Vogt believes this method is less reliable; because the battery state value is estimated through the battery management system.
The German expert continued: "In all measurement methods, companies reach a data set from car models, so that the measured values can be compared with the values of new cars."
One can conduct battery state tests at many car repair workshops, testing and inspection bodies, and automobile clubs, and the cost varies depending on the type of test chosen, whether it's a quick test or a premium version. Quick tests are usually carried out while the car is stationary, while the more comprehensive battery state tests take a day or several days and the car is running.
The testing authority Dekra focuses in its testing primarily on measuring the battery's internal resistance.
Michel Tziatzios from the German testing authority said: "This testing method is done by loading the battery rapidly; data is collected by accelerating the car for approximately 100 meters." In addition, the German testing authority is developing a second method through which the car battery is briefly charged. He confirmed that combining the two methods would cover most needs: "After that, the recorded measurement data for each car model or battery type is compared with the parameters stored in cloud computing services, and algorithms finally calculate the battery's State of Health (SoH) as a percentage."
The Austrian company Aviloo, which specializes in diagnosing battery faults, relies on energy analysis in testing battery condition. Patrick Schabus from Aviloo explained: "This test requires additional measurement of internal resistance, and several factors, like cold and heat and driving style, greatly influence the result." He added: "We compensate for these impacts through internal resistance, and energy analysis allows for greater accuracy regarding the current driving range."
Rapid and frequent charging typically causes battery aging, in addition to intense acceleration, especially when the battery is not at operating temperature. The expert Schabus emphasized that battery condition testing reveals early indicators of the battery's remaining condition, which helps avoid higher repair costs.
A high battery state value indicates that it is in good condition, which significantly affects the driving range, a critical factor in the value of the electric car, hence the importance of these tests increases in the used car market.
Vogt stressed that "battery condition testing is extremely useful, especially for older cars, which have been in production for 7 or 8 years, as the battery warranty provided by many car companies ends during this period." This test is useful for those who want to buy used electric cars to determine whether the battery is faulty or damaged, and also for sellers to get a better price when selling their electric cars.
Tziatzios the expert from the Dekra testing authority noted that a good battery state value is between 80 and 100%, but even if the battery reaches 75%, there is no need to worry, as even though the driving range will not be the same as the base value, it is still effective for city traffic.
Testing the battery state is also useful if one decides to drive their electric car for a long period. Schabus explained: "It's better to perform battery condition testing, which analyzes the cell level if the driving range suddenly decreases quickly; as it can reveal a fault in the battery. Even if there is only one weak cell in the battery, it will affect the entire system." Depending on the type of fault, it may not be necessary to replace the entire battery if the problem can be solved through battery balancing.
