AUTOMOTIVE E-SSENTIALS

Batteries in electric cars: There is still no standard for “Battery SoH”

Pascal Mast, Director New Technologies and Sustainable Services at TÜV SÜD, on various methods for assessing battery performance in electric cars.

There are various methods to determine the SoH. Are all methods equally valid?

P. Mast: In fact, many different methods are now available on the market to determine a SoH value. However, these are not equivalent and sometimes rely on different parameters and references. Moreover, as there is still no standardized definition for determining the “Battery SoH”, the various methods cannot simply be compared without restriction. Incidentally, the same also applies to the manufacturer’s data read from the vehicles.

A possible SoH value can, for example, be the ratio of the amount of energy currently available in the battery to the amount of energy initially available when the battery is new. Here too, however, there are different approaches to calculate some of the parameters. Accordingly, there are (as of today) no methods or results that are equivalent by definition and standardization.

So, everyone has a different understanding of the SOH?

P. Mast: The term SoH can be interpreted in various ways. The SoH is a ratio between the current condition and the new condition – usually a percentage value is given. However, the comparison can refer to different physical parameters. For example, the condition can refer to the amount of energy or the resistance of a battery. The most common reference is to the amount of energy that is currently still available in the battery. As things stand today, however, the references and boundary conditions are not fixed by definition and can therefore differ for different methods.

Are rapid tests reliable?

P. Mast: Rapid tests, which only read out individual numerical values from the vehicle control units, indicate the current values from the vehicle’s battery management systems and are therefore a snapshot. This is based on the values specified by the manufacturer. If it is a neutral and vehicle-independent SoH determination, the battery must be stressed or loaded.

Does the SoH allow conclusions to be drawn about safety?

P. Mast: From TÜV SÜD’s point of view, the SoH value should be part of a more complex safety assessment. We refer to this safety assessment as a battery “State of Safety” (SoS) check. However, it is not possible to draw any useful conclusions about battery safety by looking at the SoH value alone.

When will such a measurement standard for SoH be available?

P. Mast: It is also one of our tasks to develop and establish appropriate standards with the industry, technology providers, standardizers, and regulators. The topic of “battery condition” is also becoming increasingly present in the negotiations on the new Euro 7 emissions standard, and a uniform standard must therefore be developed. In the Euro 7 standard, which has not yet been adopted, the battery status is referred to as SoCE (State of Certified Energy) and SoCR (State of Certified Range). The data is classified according to data already recorded for batteries of the same type and compared with the original capacity of the vehicle model.

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