The health status of an electric vehicle’s battery remains the biggest question mark for potential buyers. The SoH (State of Health) was introduced as a metric to provide insight into the current condition of the battery, making it a key indicator. However, SoH cannot be measured directly, it reflects the battery’s condition in relation to its original state.
“SoH is not always SoH,” explained Patrick Schabus, Chief Product Officer, AVILOO. “There are different reference values and calculation methods, which can lead to significantly varying results.”
Different reference values: capacity vs. energy
The capacitive SoH is based on the remaining capacity of the battery in ampere-hours. While it is theoretically independent of temperature and driving behaviour, in practice it is influenced by both. Additionally, internal resistance is not considered, which can lead to an overestimation of the actual range.
“Increased internal resistance reduces range, especially in older vehicles, the capacitive SoH is often too optimistic,” said Schabus.
The energetic SoH, on the other hand, measures the usable energy in kilowatt-hours and is directly linked to range. “If a vehicle has 90% energetic SoH, it means that 90% of its original range is still available,” Schabus continued. However, the calculation is complex, as it depends on temperature and load profile. At AVILOO, it is standardised according to the WLTP cycle at 23 °C.
Calculation methods: pack vs. cell level
The method of calculation affects the reliability of the SoH furthermore. The simplest approach is to calculate it at pack level, but this only provides rough estimates, as it lacks data on individual cells. Much more precise is the cell-level analysis, where the state of charge of each individual cell is recorded, including balancing status. Two methods are used to determine the overall SoH:
Average cell: a widely used but imprecise method, as it does not adequately account for the weakest cells.
Weakest cell: the most accurate method, where the weakest cell determines the overall condition, comparable to the weakest link in a chain.
The AVILOO approach: State of Certified Energy (SoCE)
AVILOO relies on the State of Certified Energy (SoCE), an energetic SoH at cell level based on the internationally recognised GTR22 standard. The usable energy is measured under defined conditions, and the weakest cell is used for calculation.
“Our goal is to precisely represent a vehicle’s actual range in relation to its original state, transparent, traceable, and independent,” said Schabus.
The AVILOO PREMIUM Test is one of the world’s most accurate analysis product for used EV batteries. During a test drive, high-resolution data such as current, cell voltage, and temperature are recorded in real time and processed in the AVILOO Cloud. The analysis is performed at cell level and considers essential parameters such as internal resistance, time constants, and resting voltage curves.
“Our cell models are based on extensive lab measurements of real vehicle modules,” said Schabus. “Only this way can we determine the state of charge of each individual cell with precision – far more accurately than the vehicle’s Battery Management System (BMS).”
The result is a certified battery certificate that transparently and reliably shows the vehicle’s actual remaining range—a decisive advantage for dealers, fleet managers, and buyers.
For situations requiring quick decisions – such as in vehicle trading or service cases – AVILOO provides the FLASH Test. It is based on a machine learning model trained on tens of thousands of PREMIUM tests. Using predictors such as vehicle age, mileage, and charging behaviour, the SoH is reliably determined in just three minutes, without fully discharging the battery.
“The FLASH Test is ideal for fast assessments without compromising accuracy,” said Schabus. “It shows how data-driven innovation creates real value.”
Conclusion
Battery health assessment is complex, and the SoH value alone is often not enough. Buyers and dealers should not blindly trust reported values but rely on certified, independent tests. With its battery certificate, AVILOO offers a reliable solution for greater transparency and security in the used EV market.
