Method and system for rapidly measuring and calculating self-discharge characteristic of battery

Abstract

The invention discloses a method and system for rapidly measuring and calculating the self-discharge characteristic of a battery, and the method comprises the steps: setting preset measurement and calculation time T, and determining the electric quantity Q which needs to be charged by a to-be-measured battery; determining timing starting time and initial open-circuit voltage of the to-be-tested battery, and then charging the to-be-tested battery with the electric quantity Q and standing the to-be-tested battery; when the timing time reaches a set value, re-measuring the open-circuit voltage of the battery to be measured; if the open-circuit voltage at the moment is smaller than the initial open-circuit voltage, the to-be-detected battery is judged to be abnormal; otherwise, performing voltage curve fitting on the subsequent standing process, judging whether the time for returning the open-circuit voltage to the initial open-circuit voltage is within the measurement time T or not based on a fitting curve, if so, continuing to naturally stand until the open-circuit voltage returns to the initial open-circuit voltage, and calculating the self-discharge current of the battery; and if not, accelerating battery discharge until the initial open-circuit voltage is returned, and calculating the self-discharge current of the battery. The method can greatly shorten the test time and improve the test efficiency.

Description

Technical Field

[0001] This invention relates to the field of battery testing technology, and in particular to a method and system for rapidly calculating the self-discharge characteristics of a battery. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Self-discharge refers to the phenomenon where a battery naturally loses electrical charge due to internal chemical reactions when it is not connected to a load or in use. In practical applications and battery manufacturing processes, testing the battery's self-discharge rate is crucial, as it not only affects end-use performance but also reflects the level of manufacturing quality.

[0004] Self-discharge rate measures a battery's ability to retain charge during storage or idle conditions, and is a key indicator for determining whether it is suitable for high-stability scenarios such as backup power, energy storage systems, or long-term storage.

[0005] For battery manufacturers, measuring self-discharge rate not only helps screen cells with potential internal short circuits, material defects, or aging tendencies, improving product reliability and safety, but also provides important basis for optimizing material systems and processes, thereby improving product consistency, meeting the performance needs of different customers, and enhancing market competitiveness.

[0006] In existing technologies, the self-discharge rate is generally measured using the static method, a basic but time-consuming assessment technique. The core process involves fully charging the battery to its rated capacity, then placing it in a strictly controlled temperature and humidity environment (e.g., 25℃±1℃, humidity below 60%), periodically measuring the battery's open-circuit voltage (OCV) or remaining capacity decay. Since self-discharge is essentially a slow chemical side reaction within the battery, the static method requires observation periods of several weeks or even months to accumulate significant quantifiable data. This is especially true for types with low self-discharge rates, such as lithium-ion batteries, where even longer static times are often needed to eliminate measurement errors. While this method is simple and low-cost, its efficiency is a significant bottleneck, severely restricting R&D and quality control efficiency and making it difficult to meet the demands of high-turnover scenarios.

[0007] Existing technologies also disclose methods that calculate the self-discharge rate of a single cell by measuring the voltage drop and interval time of the cell or module when it comes off the production line and before it is reassembled, based on the cell's OCV-SOC characteristic data. Compared to calculating the self-discharge rate by measuring capacity loss after a period of rest, this method has advantages such as saving testing equipment resources and storage space. However, this method only discharges at a fixed rate and cannot adapt to the characteristic requirements of different battery types. Summary of the Invention

[0008] To address the aforementioned issues, this invention proposes a method and system for rapidly calculating battery self-discharge characteristics. By charging the battery with a certain amount of power, the self-discharge rate is calculated based on the terminal voltage data during the subsequent self-discharge process. Simultaneously, it enables accurate and rapid screening of batteries with abnormal self-discharge.

[0009] In some implementations, the following technical solutions are adopted: A method for rapid calculation of battery self-discharge characteristics includes: Set a predetermined measurement time T, and determine the amount of charge Q required for the battery under test; Determine the start time and the initial open-circuit voltage of the battery under test, then charge the battery under test with the specified amount Q and let it stand. When the timing reaches the set value, the open-circuit voltage of the battery under test is measured again. If the open-circuit voltage at this time is less than the initial open-circuit voltage, the battery under test is determined to be abnormal. Otherwise, the voltage curve is fitted to the subsequent resting process. Based on the fitted curve, it is determined whether the time taken for the open-circuit voltage to return to the initial open-circuit voltage is within the calculated time T. If it is, the battery continues to rest naturally until it returns to the initial open-circuit voltage, and the battery self-discharge current is calculated. If it is not, the battery discharge is accelerated until it returns to the initial open-circuit voltage, and the battery self-discharge current is calculated.

[0010] As a further step, the required charge Q for the battery under test is determined, specifically as follows: The required charge Q for the battery under test is calculated based on the product of the predetermined measurement time T and the maximum self-discharge current of the battery under test.

[0011] As a further option, the predetermined calculation time T is set according to the battery type and must be greater than the time required for the battery to completely eliminate the polarization effect, with T being no less than 2 hours.

[0012] As a further step, voltage curve fitting is performed on the subsequent settling process, specifically as follows: Voltage curves were fitted to the subsequent settling process using the least squares method to obtain multiple voltage data points during the settling phase. Based on voltage data Perform fitting; where, For the i-th time, This represents the battery voltage at the i-th time point; Determine that each data point The least squares coefficients that minimize the sum of squared distances to their corresponding fitted values.

[0013] As a further solution, if the time taken for the open-circuit voltage to return to the initial open-circuit voltage is within the measurement time T based on the fitted curve, then the battery self-discharge current is calculated as follows: the battery self-discharge current is obtained by the ratio of the amount of charge Q required to be added to the battery under test to the time taken for the battery voltage to return to the initial open-circuit voltage under natural rest.

[0014] As a further solution, if the time taken for the open-circuit voltage to return to the initial open-circuit voltage, based on the fitted curve, is not within the calculated time T, the battery discharge can be accelerated. The specific method is as follows: Connect the battery under test in parallel with an external resistor of a set resistance value; The maximum resistance value of the external resistor is determined based on the ratio of the initial open-circuit voltage of the battery under test to the battery's maximum self-discharge current.

[0015] As a further option, if the time taken for the open-circuit voltage to return to the initial open-circuit voltage, based on the fitted curve, is not within the measurement time T, then the battery self-discharge current calculation method is as follows: The external circuit charge loss is determined by integrating the ratio of the measured voltage to the external resistance during the battery's accelerated discharge process; the self-discharge charge loss is determined based on the required charge Q of the battery under test and the external circuit charge loss; and the battery self-discharge current is determined based on the ratio of the self-discharge charge loss to the time it takes for the battery voltage to return to the initial open-circuit voltage under accelerated discharge.

[0016] As a further embodiment, the battery self-discharge current is specifically: ; in, This is the battery's self-discharge current. This is the measured voltage during the battery's accelerated discharge process. For external resistors, To start the timing, This is the time when the timer reaches the set value. To accelerate the time it takes for the battery voltage to return to its initial open-circuit voltage during battery discharge.

[0017] As a further solution, when the timing reaches the set value, the open-circuit voltage of the battery under test is remeasured. The set value is the time within the range of [T / 3, 2T / 3], where T is the predetermined measurement time.

[0018] In other embodiments, the following technical solutions are adopted: A rapid battery self-discharge characteristic measurement system includes: The charge level determination module is configured to determine the charge level Q required for the battery under test. The charging module is configured to determine the start time and the initial open-circuit voltage of the battery under test, and then charge the battery under test with the amount of power Q and let it stand. The test module is configured to remeasure the open-circuit voltage of the battery under test when the timing reaches a set value. If the open-circuit voltage is less than the initial open-circuit voltage, the battery under test is determined to be abnormal. Otherwise, the voltage curve is fitted during the subsequent resting process. Based on the fitted curve, it is determined whether the time taken for the open-circuit voltage to return to the initial open-circuit voltage is within the calculated time T. If it is, the battery continues to rest naturally until it returns to the initial open-circuit voltage, and the battery self-discharge current is calculated. If it is not, the battery discharge is accelerated until it returns to the initial open-circuit voltage, and the battery self-discharge current is calculated.

[0019] Compared with the prior art, the beneficial effects of the present invention are: (1) In the test process, the method of the present invention determines whether the calculation time is within the preset calculation time by fitting the subsequent voltage curve midway. If it is within the preset calculation time, the static test is carried out normally. If not, the battery discharge is accelerated by connecting an external resistor, thereby ensuring that the battery self-discharge characteristics can be calculated within the preset calculation time. The preset calculation time is usually around 10 hours, which can greatly shorten the test time and improve the test efficiency compared with the several weeks or months of the prior art.

[0020] (2) After a period of normal testing, the present invention can determine whether the battery is abnormal based on the relationship between the battery open circuit voltage and the initial open circuit voltage, thereby enabling the rapid screening of batteries with abnormal self-discharge.

[0021] (3) The method of the present invention only requires the use of a battery testing and data acquisition device to collect battery voltage data to complete the experiment. The device is easy to operate and greatly improves the experimental efficiency. At the same time, the data accuracy is improved through the subsequent data noise reduction process.

[0022] Other features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a rapid calculation method for battery self-discharge characteristics in an embodiment of the present invention; Figure 2 This is a schematic diagram of abnormal self-discharge battery voltage changes in an embodiment of the present invention; Figure 3 This is a schematic diagram of the subsequent fitting voltage change of a normal self-discharge battery in an embodiment of the present invention; Figure 4 This is a schematic diagram of the battery connected in parallel with an external resistor in an embodiment of the present invention; Figure 5 This is a schematic diagram of voltage changes during the self-discharge process accelerated by the parallel external resistor in an embodiment of the present invention; Figure 6 This is a voltage variation diagram of battery cell 1 in an embodiment of the present invention; Figure 7 This is a voltage variation diagram of battery cell 2 in an embodiment of the present invention. Detailed Implementation

[0024] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0026] Example 1 In one or more embodiments, a method for rapidly calculating the self-discharge characteristics of a battery is disclosed, combined with... Figure 1 Specifically, it includes the following process: S101: Determine the amount of charge Q required for the battery under test.

[0027] Specifically, the amount of charge Q required for the battery under test is based on a predetermined measurement time T and the battery's maximum self-discharge current I. lim The product is determined, that is: .

[0028] The calculation time T is the time required to complete the self-discharge current calculation.

[0029] To ensure measurement accuracy, the measurement time T needs to be set according to the battery type and must be greater than the time required for the battery to completely eliminate polarization (eliminating voltage loss caused by charge transport, ion diffusion and other factors during charging and discharging). Therefore, T is usually no less than 2 hours and can generally be selected at around 10 hours.

[0030] The ultimate self-discharge current of the battery under test The specific standard is determined based on national standards or the differentiated standards of battery manufacturers; for example, according to the general specifications for lithium-ion batteries, the monthly self-discharge rate of a high-quality lithium-ion battery should be ≤3% (corresponding to the limiting current I). lim≤12mA). If this threshold is exceeded, the battery is considered to have defects such as micro-short circuit or electrolyte decomposition. Different battery manufacturers have different self-discharge standards, with energy storage batteries (long cycle life batteries) having stricter requirements than power batteries; I is determined. lim It is necessary to make differentiated adjustments based on the battery models of different battery manufacturers.

[0031] The calculated charge Q is much smaller than the charge required to fully charge the battery, so the charging time and the time required for the battery to be discharged are both relatively short.

[0032] S102: Determine the start time and the initial open-circuit voltage of the battery under test, then charge the battery under test with charge Q and let it stand.

[0033] In this embodiment, the time t1 at the start of the experiment is recorded, and the initial open-circuit voltage of the battery is OCV1. A constant current pulse charge Q is injected into the battery, followed by a resting period. Since the pulse charge Q is very small, the charging time is much shorter than T. During the resting period, the time t and the corresponding open-circuit voltage at each time point are recorded in real time.

[0034] S103: When the timing reaches the set value, remeasure the open-circuit voltage of the battery under test; if the open-circuit voltage at this time is less than the initial open-circuit voltage, the battery under test is determined to be abnormal; otherwise, perform voltage curve fitting on the subsequent resting process, and determine whether the time taken for the open-circuit voltage to return to the initial open-circuit voltage is within the calculated time T based on the fitted curve. If it is, continue to rest naturally until it returns to the initial open-circuit voltage, and calculate the battery self-discharge current; if it is not, accelerate the battery discharge until it returns to the initial open-circuit voltage, and calculate the battery self-discharge current.

[0035] In this embodiment, the set value can be selected between [T / 3, T2 / 3], for example, T / 2 is selected in this embodiment.

[0036] When t=T / 2, measure the open-circuit voltage of the battery at this time as OCV2, and record the time as t2. Compare the relationship between OCV2 and OCV1 to confirm the subsequent operation.

[0037] (1) If OCV2 < OCV1, such as Figure 2 As shown, this indicates that the battery has completely discharged the charged capacity Q at time T / 2. Therefore, the self-discharge rate is too high and the self-discharge current exceeds the limit value, indicating that the battery is abnormal. This completes the screening of abnormal self-discharge batteries.

[0038] (2) If OCV2 > OCV1, the self-discharge rate meets the requirements, the battery is normal, and the subsequent process can continue.

[0039] The voltage curve is fitted to the subsequent settling process using the least squares method. The least squares method finds the best function match for the data by minimizing the sum of squares of the errors, so that the sum of squares of the errors between the obtained unknown data and the actual data is minimized.

[0040] Assume the voltage data of a single cell during the resting phase is as follows: ; in, This represents the i-th time. This represents the voltage value of a single battery cell at time i.

[0041] Use it as the input for least squares, so that all data points and The sum of squares of the distances D is minimized, i.e., let: ; here, The voltage fitting value at time i is... c k These are coefficients to be determined.

[0042] After determining the coefficients, plot the fitted voltage curve until OCV=OCV1 at a certain moment, and observe whether the time t used meets the specified time, i.e., whether it satisfies the following: .

[0043] The fitting diagram is shown below. Figure 3 As shown: (1) If the specified time is met, let it stand naturally until the battery voltage recovers to OCV1, i.e., OCV3=OCV1. Record the time at this time as t3 to complete the experiment.

[0044] Battery voltage data is extracted and denoised using a Savitzky-Golay (SG) filter. This filter removes noise while ensuring that the shape and width of the signal remain unchanged, making the acquired data closer to the actual operating state of the battery.

[0045] The SG filtering smoothing formula is:

[0046] in, The smoothing coefficient is obtained by fitting a polynomial using the least squares method.

[0047] After data filtering, the battery self-discharge current is calculated as follows: .

[0048] (2) If the specified time is not met, then as follows Figure 4As shown, the battery is connected in parallel with an external resistor of a specific resistance value r to accelerate the self-discharge process. A schematic diagram of the voltage change during the self-discharge process after connecting the external resistor in parallel is shown below. Figure 5 As shown.

[0049] Firstly, based on the battery's self-discharge current limit. Determine the maximum resistance value of the resistor connected in parallel. , This allows for the subsequent connection of an external resistor r, which is smaller than the maximum resistance value, in parallel with it, i.e., r < 0. This mitigates the drawback of the external resistor suppressing battery discharge when the external resistor value is too large, due to the large voltage difference between the battery under test and the external resistor. For example... When the resistance is 10Ω, r can be 3Ω or 5Ω, etc.

[0050] It should also be noted that, according to the fitted voltage curve, the greater the deviation of the required time from the calculated time T, or the greater the deviation of the open-circuit voltage at the calculated time T from the initial open-circuit voltage, the larger the external resistance should be.

[0051] The battery was then left to stand naturally until the battery voltage returned to OCV1, completing the experiment. Data was extracted and noise reduction was performed using an SG filter. The external circuit charge loss Q... r for: ; In the formula, u represents the real-time voltage measured within t2~t3.

[0052] Then the self-discharge charge loss Q lib for: ; The self-discharge current is calculated as follows: ; It should be noted that the self-discharge current is a direct reflection of the self-discharge rate, and the self-discharge current focuses more on the immediate current loss of the battery.

[0053] Table 1 lists the main testing instruments used in this experiment and their uses. The selection of each instrument aims to ensure the comprehensiveness and accuracy of the experiment, so as to conduct in-depth analysis of the battery's charge-discharge characteristics, state monitoring, and self-discharge.

[0054] Experimental verification This experiment will use these devices to test, evaluate and calculate the battery self-discharge related performance, as shown in Table 1.

[0055] Table 1. Detection instruments used in the experiment

[0056] By consulting the battery's user manual, this battery I lim The calculation formula is: ; The self-discharge test duration T is taken as 10 hours, and the charging capacity Q is calculated as follows: ; The experiment used two individual battery cells, cell 1 and cell 2. The above operations were performed on each cell, and the voltage changes were as follows: Figure 6 and Figure 7 As shown.

[0057] Depend on Figure 6 It can be seen that OCV2 < OCV1, indicating that cell 1 has completely discharged the charged capacity Q at T / 2, the self-discharge rate is too high and the self-discharge current exceeds the limit value, the battery is abnormal, therefore cell 1 is an abnormal battery.

[0058] Depend on Figure 7 It can be seen that OCV2>OCV1. Fitting the subsequent process, it is found that when the battery open-circuit voltage recovers to OCV1, the time taken is much longer than T. Therefore, a parallel resistor needs to be connected to the battery to speed up the calculation process.

[0059] ; It can be seen that the resistance should be less than 296Ω. If the resistance is too large, the effect of accelerating self-discharge will not be obvious, and the measurement cannot be completed within the specified time. If the resistance is too small, it will be greatly affected by battery polarization, reducing the accuracy of the measurement.

[0060] Therefore, after comprehensive comparison, a 20Ω resistor is selected. When t=17761s, OCV3 = OCV1. Therefore, the self-discharge current of the battery can be calculated as follows: .

[0061] In summary, the method of this embodiment can determine whether the battery is abnormal after a period of normal testing based on the relationship between the battery open-circuit voltage and the initial open-circuit voltage, thereby enabling the rapid screening of batteries with abnormal self-discharge.

[0062] In this embodiment, the method determines whether the calculation time is within the preset calculation time by fitting the subsequent voltage curve midway through the test. If it is within the preset calculation time, the static test is carried out normally. If not, the battery discharge is accelerated by connecting an external resistor, thereby ensuring that the battery self-discharge characteristics can be calculated within the preset calculation time. Compared with the previous technology of several weeks or months, this method can greatly shorten the test time and improve the test efficiency.

[0063] Example 2 In one or more embodiments, a rapid battery self-discharge characteristic measurement system is disclosed, comprising: The charge level determination module is configured to determine the charge level Q required for the battery under test. The charging module is configured to determine the start time and the initial open-circuit voltage of the battery under test, and then charge the battery under test with the amount of power Q and let it stand. The test module is configured to remeasure the open-circuit voltage of the battery under test when the timing reaches a set value. If the open-circuit voltage is less than the initial open-circuit voltage, the battery under test is determined to be abnormal. Otherwise, the voltage curve is fitted during the subsequent resting process. Based on the fitted curve, it is determined whether the time taken for the open-circuit voltage to return to the initial open-circuit voltage is within the calculated time T. If it is, the battery continues to rest naturally until it returns to the initial open-circuit voltage, and the battery self-discharge current is calculated. If it is not, the battery discharge is accelerated until it returns to the initial open-circuit voltage, and the battery self-discharge current is calculated.

[0064] It should be noted that the specific implementation methods of the above modules are the same as those in Embodiment 1, and will not be described in detail here.

[0065] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for rapidly calculating the self-discharge characteristics of a battery, characterized in that, include: Set a predetermined measurement time T, and determine the amount of charge Q required for the battery under test; Determine the start time and the initial open-circuit voltage of the battery under test, then charge the battery under test with the specified amount Q and let it stand. When the timing reaches the set value, the open-circuit voltage of the battery under test is measured again. If the open-circuit voltage at this time is less than the initial open-circuit voltage, the battery under test is determined to be abnormal. Otherwise, the voltage curve is fitted to the subsequent resting process. Based on the fitted curve, it is determined whether the time taken for the open-circuit voltage to return to the initial open-circuit voltage is within the calculated time T. If it is, the battery continues to rest naturally until it returns to the initial open-circuit voltage, and the battery self-discharge current is calculated. If it is not, the battery discharge is accelerated until it returns to the initial open-circuit voltage, and the battery self-discharge current is calculated.

2. The method for rapid calculation of battery self-discharge characteristics as described in claim 1, characterized in that, The required charge Q for the battery under test is determined as follows: The required charge Q for the battery under test is calculated based on the product of the predetermined measurement time T and the maximum self-discharge current of the battery under test.

3. The method for rapid calculation of battery self-discharge characteristics as described in claim 2, characterized in that, The predetermined calculation time T is set according to the battery type and must be greater than the time required for the battery to completely eliminate polarization effect; T is not less than 2 hours.

4. The method for rapid calculation of battery self-discharge characteristics as described in claim 1, characterized in that, The voltage curve was fitted during the subsequent settling process, specifically as follows: Voltage curves were fitted to the subsequent settling process using the least squares method to obtain multiple voltage data points during the settling phase. Based on voltage data Perform fitting; where, For the i-th time, This represents the battery voltage at the i-th time point; Determine that each data point The least squares coefficients that minimize the sum of squared distances to their corresponding fitted values.

5. The method for rapid calculation of battery self-discharge characteristics as described in claim 1, characterized in that, If the time taken for the open-circuit voltage to return to the initial open-circuit voltage is within the measurement time T based on the fitted curve, then the battery self-discharge current is calculated as follows: the battery self-discharge current is obtained by the ratio of the amount of charge Q required for the battery under test to the time taken for the battery voltage to return to the initial open-circuit voltage under natural rest.

6. The method for rapid calculation of battery self-discharge characteristics as described in claim 1, characterized in that, If the time taken for the open-circuit voltage to return to the initial open-circuit voltage, based on the fitted curve, is not within the calculated time T, the battery discharge can be accelerated. The specific method is as follows: Connect the battery under test in parallel with an external resistor of a set resistance value; The maximum resistance value of the external resistor is determined based on the ratio of the initial open-circuit voltage of the battery under test to the battery's maximum self-discharge current.

7. The method for rapid calculation of battery self-discharge characteristics as described in claim 1, characterized in that, If the time taken for the open-circuit voltage to return to the initial open-circuit voltage, based on the fitted curve, is not within the calculated time T, then the battery self-discharge current is calculated as follows: The external circuit charge loss is determined by integrating the ratio of the measured voltage to the external resistance during the battery's accelerated discharge process; the self-discharge charge loss is determined based on the required charge Q of the battery under test and the external circuit charge loss; and the battery self-discharge current is determined based on the ratio of the self-discharge charge loss to the time it takes for the battery voltage to return to the initial open-circuit voltage under accelerated discharge.

8. The method for rapid calculation of battery self-discharge characteristics as described in claim 7, characterized in that, The battery self-discharge current is specifically: ； in, This is the battery's self-discharge current. This is the measured voltage during the battery's accelerated discharge process. For external resistors, To start the timing, This is the time when the timer reaches the set value. To accelerate the time it takes for the battery voltage to return to its initial open-circuit voltage during battery discharge.

9. A method for rapid calculation of battery self-discharge characteristics as described in claim 1 or 8, characterized in that, When the timing reaches the set value, the open-circuit voltage of the battery under test is measured again. The set value is the time within the range of [T / 3, 2T / 3], where T is the predetermined measurement time.

10. A system for rapidly calculating the self-discharge characteristics of a battery, characterized in that, include: The charge capacity determination module is configured to: set a predetermined measurement time T, and determine the charge capacity Q required for the battery under test; The charging module is configured to: determine the start time and the initial open-circuit voltage of the battery under test, then charge the battery under test with the amount of power Q and let it stand still; The test module is configured to: when the timing reaches a set value, remeasure the open-circuit voltage of the battery under test; if the open-circuit voltage at this time is less than the initial open-circuit voltage, the battery under test is determined to be abnormal; otherwise, voltage curve fitting is performed on the subsequent resting process, and based on the fitted curve, it is determined whether the time taken for the open-circuit voltage to return to the initial open-circuit voltage is within the calculated time T. If it is, the battery continues to rest naturally until it returns to the initial open-circuit voltage, and the battery self-discharge current is calculated; if it is not, the battery discharge is accelerated until it returns to the initial open-circuit voltage, and the battery self-discharge current is calculated.

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