The rapid growth of the electric car industry globally, particularly in China, has underscored the critical role of traction batteries as the core component determining vehicle safety, performance, and longevity. In China, the development of the China EV sector relies heavily on robust standards to ensure product quality and foster innovation. The GB/T 31486 standard, specifically addressing the electrical performance requirements and test methods for traction batteries used in electric cars, has been instrumental in shaping the China EV landscape. The recent revision from the 2015 version to GB/T 31486—2024, effective from April 1, 2025, reflects advancements in battery technology and a deeper understanding of real-world operating conditions for electric cars. This analysis delves into the key changes, their implications for the China EV industry, and how they align with international practices, utilizing tables and mathematical formulations to elucidate the revisions.
The evolution of GB/T 31486 is driven by several factors, including the shift towards cell-to-pack (CTP) designs in electric car batteries, which reduces the reliance on modules, and the accumulation of operational data from China EV fleets. These data reveal that typical discharge and charge rates in electric cars are lower than previously assumed, prompting adjustments in test conditions to better simulate actual usage. For instance, analysis of driving cycles from various China EV models shows that 90% of discharge rates fall below 0.3C, and average discharge rates are consistently under 0.3C, leading to revised current rates in tests. This ensures that the standard accurately reflects the performance of electric car batteries under typical China EV operating scenarios, enhancing the relevance of test results for manufacturers and regulators.
One of the most significant changes in GB/T 31486—2024 is the shift in test objects from modules to individual cells. In the 2015 version, tests often involved modules or simulated modules, but with the trend towards CTP configurations in electric car batteries, focusing on cells allows for a more direct assessment of performance and consistency. This aligns with international standards like IEC 62660-1:2018 and eliminates redundancies, as vibration testing is now covered in other standards such as GB 38031—2020. Additionally, the sample size for testing has been increased to 30 cells, up from 10 in the previous version, to strengthen consistency evaluation—a crucial aspect for ensuring reliability in mass-produced electric car batteries for the China EV market. The table below summarizes the comparison of test items between the 2015 and 2024 versions, highlighting additions and deletions relevant to electric car applications.
| Test Item | GB/T 31486—2024 | GB/T 31486—2015 | IEC 62660-1:2018 |
|---|---|---|---|
| Room Temperature Discharge Capacity | ✓ | ✓ | ✓ |
| Room Temperature Discharge Energy | ✓ | ✓ | ✓ |
| Room Temperature Specific Energy | ✓ | ✓ | ✓ |
| Room Temperature Rate Discharge Capacity | ✓ | ✓ | |
| Room Temperature Rate Charge Capacity | ✓ | ✓ | |
| Power | ✓ | ||
| Regenerative Power | ✓ | ||
| Low Temperature Discharge Capacity | ✓ | ✓ | ✓ |
| High Temperature Discharge Capacity | ✓ | ✓ | ✓ |
| Room Temperature Charge Retention and Capacity Recovery | ✓ | ✓ | ✓ |
| Room Temperature Energy Efficiency | ✓ | ✓ | |
| High Temperature Charge Retention and Capacity Recovery | ✓ | ✓ | |
| High Temperature Energy Efficiency | ✓ | ✓ | |
| Storage | ✓ | ✓ | ✓ |
| Vibration Resistance | ✓ |
The revision also introduces updated terminology to better categorize electric car batteries. In GB/T 31486—2024, batteries are classified as high-energy or high-power based on the ratio of maximum allowable output power to discharge energy at 1C rate. For high-energy batteries, used primarily in all-electric cars in the China EV fleet, the discharge current for rating capacity has been changed from 1I1 (1-hour rate) to 1I3 (3-hour rate), reflecting real-world data where most discharges occur at lower rates. This adjustment ensures that tests mimic the actual usage patterns of electric cars, improving the predictive accuracy of battery performance in China EV applications. The capacity of a battery can be expressed mathematically as: $$C = I \times t$$ where \(C\) is the capacity in ampere-hours (Ah), \(I\) is the current in amperes (A), and \(t\) is the time in hours (h). For high-energy batteries in electric cars, this translates to a more realistic assessment under typical driving conditions.
Environmental testing conditions have been refined in GB/T 31486—2024 to enhance precision and alignment with other standards. The room temperature range is now specified as 25°C ± 2°C, compared to ±5°C in the 2015 version, reducing variability in test results—a critical factor for electric car batteries that are sensitive to temperature fluctuations. Relative humidity limits have been adjusted to 10%–90% for better consistency with GB/T 31467—2023. Moreover, the environmental adaptation process has been optimized with a dynamic termination mechanism: batteries must settle until the temperature difference from the target is within 2°C and the rate of change is below 1°C/h for at least 30 minutes, replacing fixed durations. This ensures thermal equilibrium without unnecessary delays, which is vital for efficient testing of electric car batteries in the fast-paced China EV industry. The energy efficiency during charge-discharge cycles, a new addition in the 2024 version, can be calculated using: $$\eta = \frac{E_{\text{discharge}}}{E_{\text{charge}}} \times 100\%$$ where \(\eta\) is the energy efficiency percentage, \(E_{\text{discharge}}\) is the discharge energy, and \(E_{\text{charge}}\) is the charge energy. This metric is crucial for evaluating the overall performance of electric car batteries, as higher efficiency translates to longer range and better energy utilization in China EV models.
Test equipment requirements have been updated to address factors like airflow, which can impact results. In GB/T 31486—2024, test chambers must maintain a wind speed below 1.7 m/s, or use tooling to minimize airflow effects, ensuring that measurements accurately represent battery behavior in electric cars. Data recording intervals have been tightened to every 100 seconds or less for general tests and 100 milliseconds for rate-dependent tests, providing higher resolution for analyzing dynamic performance in China EV applications. The following table compares the technical requirements and test methods between the two versions, emphasizing changes that affect electric car battery evaluations.
| Item | 2015 Version Object | 2015 Version Method | 2015 Version Indicator | 2024 Version Object | 2024 Version Method | 2024 Version Indicator |
|---|---|---|---|---|---|---|
| Room Temperature Discharge Capacity | Cell & Module | 1I1 discharge | ≥ rated capacity, ≤110% | Cell | High-energy: 1I3 discharge; High-power: 1I1 discharge | ≥ rated capacity, ≤110% |
| Room Temperature Rate Discharge Capacity | Module | High-energy: 3I1 discharge; High-power: 8I1 discharge | High-energy: ≥90% initial capacity; High-power: ≥80% initial capacity | Cell | High-energy: 3I3 discharge; High-power: 10I1 discharge | High-energy: ≥95% initial capacity; High-power: ≥80% initial capacity |
| Room Temperature Rate Charge Capacity | Module | 2I1 charge, then discharge | ≥80% initial capacity | Cell | Charge in ≤30 min, then discharge | ≥80% initial capacity |
| Low Temperature Discharge Capacity | Module | -20°C discharge | ≥70% initial capacity | Cell | -20°C discharge | ≥70% initial capacity |
| High Temperature Discharge Capacity | Module | 55°C discharge | ≥90% initial capacity | Cell | 45°C discharge | ≥95% initial capacity |
| Room Temperature Charge Retention | Module | 100% SOC, room temperature, 28 days | Retained capacity ≥85%, recovered ≥90% | Cell | 100% SOC, room temperature, 30 days | Retained capacity ≥90%, recovered ≥95%; range ≤5% |
| High Temperature Charge Retention | Module | 100% SOC, 55°C, 7 days | Retained capacity ≥85%, recovered ≥90% | Cell | 100% SOC, 45°C, 7 days | Retained capacity ≥90%, recovered ≥95%; range ≤5% |
| Storage | Module | 50% SOC, 45°C, 28 days | Recovered capacity ≥90% | Cell | 50% SOC, 45°C, 30 days | Recovered capacity ≥95%; range ≤5% |
| Vibration Resistance | Module | 10-55 Hz, 3 hours | No abnormalities | Deleted | Deleted | Deleted |
Performance indicators have been elevated in GB/T 31486—2024 to push the boundaries of electric car battery technology in the China EV sector. For example, the room temperature rate discharge capacity requirement for high-energy batteries has increased from 90% to 95% of initial capacity, reflecting improvements in cell design and materials. Similarly, high-temperature discharge capacity now demands at least 95% of initial capacity at 45°C, up from 90% at 55°C, aligning with typical thermal management in electric cars where batteries rarely exceed 45°C. Charge retention tests now include energy efficiency and consistency checks, with all samples requiring a range of no more than 5% for retained capacity, recovered capacity, and energy efficiency. This emphasis on consistency is vital for the scalability of China EV production, as it reduces performance variations across vehicles. The power capability of a battery, though not included in GB/T 31486, can be related to internal resistance through: $$P = I^2 R$$ where \(P\) is power in watts (W), \(I\) is current, and \(R\) is internal resistance. Future standards may incorporate such metrics to further enhance electric car battery evaluations.
The removal of vibration testing in GB/T 31486—2024 streamlines the standard by avoiding overlap with GB 38031—2020, which covers safety aspects including vibration. This allows manufacturers to focus on electrical performance without redundant tests, accelerating the development cycle for new electric car batteries in the competitive China EV market. The increased sample size to 30 cells enables a more robust assessment of production consistency, which is crucial for mass adoption of electric cars. By aligning test conditions with real-world data, such as reducing discharge rates for high-energy batteries, the standard ensures that results are predictive of actual performance in China EV applications, helping consumers make informed decisions.
In conclusion, GB/T 31486—2024 represents a significant step forward in standardizing electric car battery performance for the China EV industry. The revisions address technological trends, such as CTP designs, and refine test methods based on operational data, ensuring that batteries meet higher performance and consistency standards. This will drive innovation and quality improvements, supporting the sustainable growth of the China EV market. Looking ahead, future work could focus on developing performance grading standards to differentiate premium electric car batteries, establishing reliable power characteristic test methods, and creating evaluation frameworks for batteries throughout their lifecycle, from fresh cells to those in used or second-life applications. Such advancements will further solidify the role of standards in fostering a robust and competitive electric car ecosystem in China and beyond.