WM Motor EX5 Battery Capacity Degradation Only 2.85% After 200,000 Kilometers

Corporate News | 2020-06-16

Tuesday 16 June, 2020 - SHANGHAI. Many of the concerns surrounding the range, reliability, safety and convenience of electric vehicles (EV’s) can only be addressed through the rigorous testing and provision of good data to support or negate prevailing conceptions. Many electric vehicle makers globally have taken the initiative to increase public understanding of the technology by sharing non-sensitive data from their cars already on the road. Being the highly connected products that they are, EV’s can provide ample data to help us understand their operating performance and thus accelerate quality improvements.

The +200,000km EX5 at a WM Motor service centre

To help alleviate concerns surrounding one important consideration among car buyers, the degradation of EV batteries over time, WM Motor has long promoted the benefits of high-quality thermal management and battery management systems (BMS) in EV’s to maintain the long-term stability of a battery’s capacity. Data from one of WM Motor’s EX5 models purchased in January 2019 has provided an insight into the car’s long-term battery degradation rate. The driver of this EX5 undertakes lengthy commutes between Wenzhou, Ningbo and Hangzhou, among other cities, and has averaged approximately 500km daily and accumulated over 200,000km of driving since purchasing the vehicle last year. Having been brought in for a regular check-up this week, the battery was found to have degraded by only 2.85% from its original capacity.

Internal components of the +200,000km battery pack

There are multiple of factors that influence battery degradation. One such factor is the method used to charge the battery, with the general rule being that the faster a battery is charged on average, the faster that battery will degrade over its lifetime. This EX5’s capacity retention rate of 2.85% after 200,000kms would be extremely high compared to the industry standard even if the vehicle was most often charged at a slow, alternative current (AC) home charger. However, due to the vehicle owner’s long-distance travel requirements, the vehicle was charged using public fast direct current (DC) chargers approximately 90% of the time, which makes a 2.85% degradation rate even more noteworthy. At the time of testing, the vehicle had been put on charge over 1500 times.

 During servicing, WM Motor conducts a total of 48 inspection processes for the battery pack alone to determine optimal functioning in areas including electrical performance, thermal management, internal and external systems and mechanical connections. Testing also includes an EOL (End-of-Life) prognosis, where current and predicted battery degradation levels are determined.

The battery undergoing EOL offline testing

EOL prognosis involves close to 100 battery performance tests and technical examinations of elements including static cell voltage, cell pressure and temperature differences, insulation, high voltage and DC internal resistance (DCIR).

One of the key components contributing to maintaining battery longevity in WM Motor’s vehicles is the battery management system, the “brains” of the battery. WM Motor’s BMS is a proprietary system made of complex components that work to regulate the temperature and functioning of the cells and modules. The BMS maintains optimal conditions for the battery cells inside the pack by adjusting certain parameters according to data collected from internal sensors.

 In addition, through the internal design and development of the battery pack casing and modules, WM Motor has achieved mechanical systems protection and thermal management capabilities exceeding the industry standard. The battery pack casing is made of DP780 high-strength steel. Rogers BISCO silicone sealant is used to achieve IP68 water and dust resistance.

WM Motor’s Smart Manufacturing Facility in Wenzhou, Zhejiang Province

Voltage difference is another important consideration in ensuring battery longevity, as increased voltage difference between cells can affect the stability of the battery pack's high-power discharge during rapid acceleration, which in turn can harm internal components over time. Therefore, maintaining consistent voltage levels between all cells in a pack is particularly important. Notably, the average voltage difference of the battery in the car tested at 200,000 kilometers is almost unchanged from its state at the time of shipment, further demonstrating the ability of WM Motor’s proprietary BMS to regulate cell performance.