Battery pack strength testing methods, systems and electronic equipment

Abstract

This application discloses a method, system, and electronic device for testing the strength of a battery pack. The method includes: dividing the structure of the battery pack into static modules and dynamic modules; obtaining assembly parameters between the static and dynamic modules; inputting the assembly parameters into a pre-built computational model to obtain the strength of the battery pack; and judging the quality of the battery pack based on the strength. The method of this application divides the structure of the battery pack into regions to obtain different modules, and inputs the assembly parameters between the modules into a computational model to obtain the characteristics of the battery pack. It features fast calculation speed and high efficiency.

Description

Technical Field

[0001] The embodiments of this application relate to the field of battery pack testing technology, and in particular to a battery pack strength testing method, system and electronic device. Background Technology

[0002] With the development of the electric vehicle industry, the use of battery packs is increasing. Because electric vehicles encounter various complex operating conditions during operation, the battery packs are subjected to pressure or stress in various directions due to these different conditions. To enhance the battery pack's ability to cope with various operating conditions, it is necessary to test its relevant characteristics to determine whether it meets factory requirements. However, current testing methods and fixtures for battery pack characteristics vary widely in structure, and some fixture designs are unreasonable and lack vibration frequency analysis. Furthermore, existing methods for calculating battery pack characteristics are time-consuming and inefficient. Summary of the Invention

[0003] The embodiments of this application provide a battery pack strength detection method, system, and electronic device to solve the technical problems of long time consumption and low efficiency in the traditional battery pack strength calculation method in the prior art.

[0004] To address the aforementioned technical problems, embodiments of this application disclose the following technical solutions:

[0005] Firstly, a method for detecting the strength of a battery pack is provided, the method comprising:

[0006] The battery pack structure is divided into static modules and dynamic modules;

[0007] Obtain the assembly parameters between the static module and the dynamic module;

[0008] The assembly parameters are input into a pre-built computational model to obtain the strength of the battery pack;

[0009] The quality of the battery pack is determined based on the strength.

[0010] In conjunction with the first aspect, the assembly parameters include the degrees of freedom within the static module, its internal stiffness, the external load, and the stiffness at the connection between the static module and the dynamic module.

[0011] In conjunction with the first aspect, the method for constructing the computational model includes:

[0012] The computational model is constructed based on the statics and dynamics equations;

[0013] A threshold is set for the judgment of the computational model;

[0014] The static equations include:

[0015] (1)

[0016] The kinetic equations include:

[0017] (2)

[0018] Where, M This represents the quality matrix of the static module, in units of t. C This represents the damping matrix, in mm / s / N. K This represents the stiffness matrix of the static module, in N / mm. This represents the acceleration vector, in mm / s². 2 , Represents the velocity vector, in mm / s. U This represents the displacement vector, in mm.

[0019] In conjunction with the first aspect, the method for constructing the computational model based on the static equations and the dynamic equations includes:

[0020] The vibration frequency expression and the stress expression are obtained by constructing the static equation and the dynamic equation;

[0021] The computational model is obtained by combining the vibration frequency expression and the stress expression.

[0022] In conjunction with the first aspect, the expression for the vibration frequency includes:

[0023] ; (3)

[0024] in, f i Indicates the vibration frequency, measured in Hz. i Represents the circumferential angular frequency, measured in Rad / s. i The order is a positive integer.

[0025] In conjunction with the first aspect, the stress expression includes:

[0026] (4)

[0027] Where, This represents the stress at the Gaussian integration point, in MPa. This represents the elastic coefficient matrix, in MPa, which is the usual elastic modulus. This represents the strain at the Gaussian integration point.

[0028] In conjunction with the first aspect, the method for dividing the battery pack structure into blocks to obtain static and dynamic modules includes:

[0029] The battery pack is divided into multiple substructures according to its component structure;

[0030] The substructures are combined according to the assembly process to obtain a static module;

[0031] The remaining substructures are combined to form a dynamic module.

[0032] In conjunction with the first aspect, the method for determining the quality of the battery pack based on the strength includes:

[0033] The obtained intensity is compared with a threshold;

[0034] If the strength is greater than or equal to the threshold, the battery pack is of excellent quality, i.e., it meets the requirements;

[0035] If the intensity is less than the threshold, the battery pack quality is poor, i.e., it does not meet the requirements.

[0036] Secondly, a battery pack strength testing system is provided, the system comprising:

[0037] A partitioning module is used to partition the structure of the battery pack to obtain static modules and dynamic modules;

[0038] A data acquisition module is used to acquire assembly parameters between the static module and the dynamic module;

[0039] A data processing module is used to input the assembly parameters into a pre-built computational model to obtain the strength of the battery pack;

[0040] A judgment module is used to judge the quality of the battery pack based on the intensity.

[0041] Thirdly, an electronic device is provided, including a memory and a processor; the memory is used to store a computer program; the processor is used to implement, when executing the computer program, the battery pack strength detection method as described in any one of the first aspects, or to implement the battery pack strength detection method as described in any one of the first aspects using a battery pack strength detection system as described in the second aspect.

[0042] One of the above technical solutions has the following advantages or beneficial effects:

[0043] Compared with existing technologies, this application provides a battery pack strength testing method. The method includes: dividing the battery pack structure into static modules and dynamic modules; obtaining assembly parameters between the static and dynamic modules; inputting the assembly parameters into a pre-built computational model to obtain the battery pack strength; and judging the quality of the battery pack based on the strength. This method divides the battery pack structure into regions to obtain different modules, and inputs the assembly parameters between the modules into a computational model to obtain the battery pack characteristics. It features fast calculation speed and high efficiency. Attached Figure Description

[0044] The technical solution and other beneficial effects of this application will become apparent from the following detailed description of specific embodiments in conjunction with the accompanying drawings.

[0045] Figure 1 A flowchart illustrating the method of an embodiment of this application;

[0046] Figure 2 This is a schematic diagram of the battery pack structure provided in an embodiment of this application;

[0047] Figure 3 This is a schematic diagram of the modal structure provided in the embodiments of this application;

[0048] Figure 4 This is a schematic diagram of the tray structure provided in an embodiment of this application;

[0049] Figure 5 A block diagram of the system provided in the embodiments of this application.

[0050] The attached figures are labeled as follows:

[0051] 1-Bottom guard plate; 2-Lifting lug; 3-Water cooling plate; 4-Tray. Detailed Implementation

[0052] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0053] The applicant notes that current vibration analysis methods for battery packs are based on traditional calculation methods. However, these traditional methods have many limitations, especially in cross-platform design and development or the verification of multiple solutions. Calculating modal and vibration performance using these methods often requires significant time and effort, thus hindering rapid product iteration. Therefore, this application proposes a battery pack strength testing method that significantly reduces the calculation time for battery pack strength, thereby providing more valuable time for product optimization and iteration. The specific implementation is as follows:

[0054] like Figure 1 As shown in the figure, this application provides a battery pack strength testing method, the method including:

[0055] S1: Divide the battery pack structure into static modules and dynamic modules.

[0056] In this embodiment, the battery pack is first divided into multiple substructures according to component structure; the substructures are then combined according to assembly process to obtain static modules; the remaining substructures are then combined to form dynamic modules. It is conceivable that a battery pack assembly simulation analysis model is established based on the battery pack's overall assembly form, including, for example... Figure 2As shown, the structure includes a tray 4, a water-cooling plate 3, lifting lugs 2, modules, and a bottom protective plate 1. This simulation analysis model is integrated into a computer system. It constructs the aforementioned components related to the battery pack and adds corresponding parameters such as component material, component hardness, component size, and component quantity. After constructing the relevant model, simulation analysis of the battery pack is performed. Computer software analysis facilitates data reading and calculation; however, in some other embodiments, a real-world battery pack can be used as the data acquisition object.

[0057] In this embodiment, after all components of the battery pack assembly are established, each component can be labeled, and corresponding static and dynamic modules can be established according to the analysis strategy. Generally, when studying the impact of a component on the overall battery pack, that component is treated as a static module, while the individual components that need to be isolated are treated as dynamic modules. Therefore, when studying the impact of tray 4 on the overall battery pack, tray 4 is treated as a dynamic module, while other components such as water-cooled plate 3, hanging lug 2, module, and bottom protective plate 1 are treated as a whole to form a static module. It can be understood that by analyzing the static modules and the interaction between static and dynamic modules, the relationship between dynamic and static modules can be intuitively obtained, and data connections between dynamic and static modules can be established. This facilitates the establishment of the digital structure of the battery pack and makes it easier to study the iteration and replacement of the internal structure of the battery pack.

[0058] S2: Obtain the assembly parameters between the static module and the dynamic module.

[0059] In this embodiment, the assembly parameters include the degrees of freedom, internal stiffness, external load, and stiffness at the connection between the static and dynamic modules. After determining the static and dynamic modules, the material type of each component on the static module needs to be obtained, such as metal, plastic, or other materials. The specific material can be determined according to the actual situation. Next, the connection relationship between the components needs to be obtained, such as threaded connection, snap-fit ​​connection, or other connection methods. Then, the properties of each component and the interaction forces between the components under interaction need to be obtained, such as the mass of each component, internal and external stiffness, damping at the connection, force at the connection, and load on each surface. After measuring the relevant values ​​of multiple points of each component, a matrix is ​​formed. After obtaining the above data, the static module is encapsulated, and the encapsulated static module is characterized using the above data. After encapsulation, the connection points between the static and dynamic modules are established using ASET or ASET1.

[0060] In this embodiment, when acquiring data from static or dynamic modules, relevant keyword cards can be created. These keyword cards provide a clear visual representation of the relevant parameter values ​​for each component. Calculation methods such as CBN or GUYAN are typically used, with a frequency range set, such as 0-400Hz. Boundary conditions can also be created on the static module to represent constraints at the connection points between the static and dynamic modules. These conditions are typically created using keywords such as ASET or ASET1.

[0061] S3: Input the assembly parameters into the pre-built computational model to obtain the strength of the battery pack;

[0062] First, a computational model is constructed based on the statics and dynamics equations;

[0063] First, the static equations are constructed based on the static expression, which is:

[0064] (5)

[0065] Where, K Represents the stiffness matrix of a static module, in N / mm. U This represents the displacement vector, in mm. f This indicates the external load, measured in N (N).

[0066] Combining static expressions, the static equations for the static module superelement are constructed as follows:

[0067] (1);

[0068] in, K oo This represents the internal stiffness matrix of the static module, in N / mm. K aa This represents the stiffness matrix at the connection between the static module and the dynamic module, in N / mm. K oa This represents the stiffness matrix at the coupling point between the internal and external parts of the static module, in N / mm. P This represents the load vector at the internal components and connections of the static module, in units of N. u o The displacement of the static module represents its internal degrees of freedom, in mm. u a surface The displacement of the connection point is shown in mm.

[0069] The system dynamic equations without considering external forces include:

[0070] (2)

[0071] Where, M This represents the quality matrix of the static module, in units of t. C This represents the damping matrix, in mm / s / N. K This represents the static module stiffness matrix, in N / mm. This represents the acceleration vector, in mm / s². 2 , Represents the velocity vector, in mm / s. U This represents the displacement vector, in mm.

[0072] The vibration frequency expression and the stress expression are obtained by constructing the static equation and the dynamic equation;

[0073] If we assume that its displacement has the following motion pattern... u = u o sin( ω If the damping of the static module is not considered, the stiffness matrix and mass matrix of the static module can be obtained by solving the dynamic equations.

[0074] By solving (2), its force equation can be obtained as follows:

[0075] (6)

[0076] Where, This represents the mass matrix of the nodes within the static module, in units of t. This represents the stiffness matrix of the nodes inside the static module, in N / mm. K aa Here is the stiffness matrix at the connection point of the static module, in N / mm. K oa The stiffness matrix at the coupling point between the interior and interface of the static module is expressed in N / mm. This represents the mass matrix of the nodes at the static module interface, in units of t; u o The displacement of the static module represents its internal degrees of freedom, in mm. u a surface The displacement of the connection point is shown in mm.

[0077] By solving equation (6), we can obtain:

[0078] (7);

[0079] in, K Represented as the overall stiffness matrix of the static module, in N / mm.M The mass matrix of the static module, in units of t. The natural frequency of the static module, in Rad / s. U This is the displacement vector, in mm.

[0080] The methods for expanding equation (1) and then reducing its terms to obtain the reduced expression include:

[0081] ; (8)

[0082] ; (9)

[0083] Phase shifting of formulas (8) and (9) yields:

[0084] ; (10)

[0085] (11)

[0086] After reducing the stiffness matrix, we get:

[0087] ;(12)

[0088] The load matrix is ​​reduced to the following:

[0089] ; (13)

[0090] The mass matrix is ​​reduced to the following:

[0091] ;(14)

[0092] Integrating formulas (12), (13), and (14) yields the reduced expression:

[0093] ; (15)

[0094] The first parameter expression is obtained based on the reduced term expression and the force equation;

[0095] Phase shifting of the reduced expression yields the eigenvalues:

[0096] (16)

[0097] According to the force equation, we can obtain:

[0098] (17)

[0099] And further, we obtained:

[0100] (18)

[0101] Therefore, the expression for vibration frequency can include:

[0102] ; (3)

[0103] in, f i Indicates the vibration frequency, measured in Hz. i Represents the circumferential angular frequency, measured in Rad / s. i The order is a positive integer.

[0104] Introducing boundary conditions and combining them with equation (5), the displacement is solved:

[0105] (19)

[0106] Where, Let B represent the strain at the Gaussian integration point, and let B be the geometric matrix, determined according to the type of component material. The strain at the Gaussian integration point can be calculated according to equation (19). Then, based on Hooke's Law, the stress is derived, and the stress expression includes:

[0107] (4)

[0108] Where, This represents the stress at the Gaussian integration point, in MPa. This represents the elastic coefficient matrix, in MPa, which is the usual elastic modulus. This represents the strain at the Gaussian integration point. Through analysis and solving for the parameters, a certain mode of the static module can be obtained, such as... Figure 3 As shown.

[0109] In this embodiment, after calculating the parameters of the static module, the static module and the dynamic module are connected to perform static performance calculations for the entire battery pack. The key connection method includes: First, the load-bearing capacity of the dynamic module is calculated and its association settings are configured. In the software described above, the result files are interconnected using keywords to achieve the connection between the static and dynamic modules. The result file includes module-cool-dhb.h3d, and keywords include ASSIGN, H3DDMIG, module, module-cool-dhb.h3d, etc. Generally, keywords such as calculation output, calculation conditions, and calculation boundaries are required. Second, the load-bearing capacity of the dynamic module is calculated, generally including displacement, stress, and strain energy. Then, the working condition reference settings of the dynamic module are calculated, mainly used to calculate the modulus displacement, stress, and strain energy of the entire battery pack, as well as boundary conditions and working conditions. This generally includes the reference boundary condition keywords SPC, static FORCE, and LOAD. Subsequently, the boundary settings of the dynamic module are calculated, generally including the constraint boundaries of the bolt mounting points for the entire battery pack and the load application positions. Finally, the reference settings of the dynamic module are calculated, such as the discrete model of the dynamic module.

[0110] In this embodiment, after calculating the parameters of the dynamic and static modules, the compression resistance of the battery pack is calculated. This includes: obtaining keyword settings for the battery pack compression resistance solution, which generally includes referencing the calculation results of the static module and keywords such as SPC, Load, and various stresses used to calculate the compression resistance. Subsequently, the battery pack compression resistance working condition references are calculated, generally including keyword references such as the entire battery pack constraint boundaries and compression loads. Then, the battery pack compression resistance dynamic module references are calculated.

[0111] S4: Judge the quality of the battery pack based on its strength.

[0112] The obtained strength is compared with a threshold. If the strength is greater than or equal to the threshold, the battery pack quality is considered excellent, meeting the requirements; if the strength is less than the threshold, the battery pack quality is considered poor, failing to meet the requirements. It is understandable that, considering the nonlinear constitutive relationship of the material, under external load, the material gradually enters the plastic stage after the elastic stage, at which point plastic stress and plastic strain are obtained. Finally, the obtained stress or strain results of the battery pack structure are comprehensively evaluated against the threshold. If the requirements are not met, further optimization and improvement are carried out.

[0113] like Figure 4As shown in Table 1, taking tray 4 in the battery pack as an example, the load-bearing characteristics of tray 4 are calculated using this method and compared with the traditional method. The maximum deformation or displacement of tray 4 calculated by the traditional method is 0.3833 mm, while the maximum deformation or displacement calculated by this method is 0.3725 mm. The difference between the two is 2.82%, and the error is less than 5%, which meets the requirements. At the same time, for a battery pack with 6,517,257 cells, the traditional method takes 5 hours, 15 minutes and 31 seconds, while the method of this application only takes 4 minutes and 21 seconds, which is significantly effective.

[0114] Table 1 Comparison of Load-Bearing Analysis Results

[0115]

[0116] Similarly, the compression resistance characteristics of the entire battery pack assembly were calculated based on the created static module. The results were compared with those of traditional methods, as shown in Table 2. The maximum displacement in the X direction calculated using the traditional method was 2.457 mm, while the method of this application calculated 2.434 mm, a difference of 0.936%, with an error of less than 5%. The maximum displacement in the Y direction calculated using the traditional method was 172.102 mm, while the method of this application calculated 170.336 mm, a difference of 1.026%, with an error of less than 5%, both meeting the requirements. The X and Y directions are perpendicular to each other. Furthermore, the calculation time using the traditional method was 9 hours, 32 minutes, and 23 seconds, while the method of this application took only 4 minutes and 33 seconds, demonstrating a significant improvement. Therefore, the method of this application not only has high calculation efficiency and speed but also high accuracy.

[0117] Table 2 Comparison of Compression Resistance Analysis Results

[0118]

[0119] This application also provides a battery pack strength testing system. The system uses any of the above-described battery pack strength testing methods to test the strength of the battery pack. The system includes a division module, a data acquisition module, a data processing module, and a judgment module. The division module is used to divide the structure of the battery pack into static modules and dynamic modules; the data acquisition module is used to acquire the assembly parameters between the static modules and the dynamic modules; the data processing module is used to input the assembly parameters into a pre-built calculation model to obtain the strength of the battery pack; and the judgment module is used to judge the quality of the battery pack based on the strength.

[0120] This application also provides an electronic device, including a memory and a processor; the memory is used to store a computer program; the processor is used to implement the battery pack strength detection method of any one of the first aspects when executing the computer program, or to implement the battery pack strength detection method of any one of the above aspects using the battery pack strength detection system described above.

[0121] In summary, the method provided in this application is logically simple, highly efficient, accurate, and reliable. It has high practical and promotional value in the field of automotive battery pack static analysis technology. The method provided in this application is highly versatile and accurate, providing technical support and reference for modal and vibration performance analysis of similar products. It can significantly shorten the iterative calculation and verification cycle for battery pack performance optimization, enabling the calculation of multiple optimization schemes within a short product development cycle. This method and approach provide ideas and references for the verification and design of similar battery pack structures.

[0122] The above provides a detailed description of a battery pack strength detection method, system, and electronic device provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for testing the strength of a battery pack, characterized in that, The method comprises: The battery pack structure is divided into static modules and dynamic modules; Obtain the assembly parameters between the static module and the dynamic module; The assembly parameters are input into a pre-built computational model to obtain the strength of the battery pack; The quality of the battery pack is determined based on the strength. The method for constructing the aforementioned computational model includes: The computational model is constructed based on the statics and dynamics equations, and the method includes: The vibration frequency expression and the stress expression are obtained by constructing the static equation and the dynamic equation; The computational model is obtained by combining the vibration frequency expression and the stress expression. A threshold is set for the judgment of the computational model; The static equations include: （1） Where, K oo This represents the internal stiffness matrix of the static module, in N / mm. K aa This represents the stiffness matrix at the connection between the static module and the dynamic module, in N / mm. K oa This represents the stiffness matrix at the coupling point between the internal and external parts of the static module, in N / mm. K oa T yes K oa The transpose matrix, in N / mm. u o The displacement of the static module represents its internal degrees of freedom, in mm. u a This indicates the displacement of the connection points, in mm. P This represents the load vector at the internal and connection points of the static module, in units of N; The kinetic equations include: （2） Where, M This represents the quality matrix of the static module, in units of t. C K represents the damping matrix, in mm / s / N, and K represents the static module stiffness matrix, in N / mm. This represents the acceleration vector, in mm / s². 2 , Represents the velocity vector, in mm / s. U This represents the displacement vector, in mm.

2. The battery pack strength testing method as described in claim 1, characterized in that, The assembly parameters include the degrees of freedom, internal stiffness, external load, and stiffness at the connection between the static module and the dynamic module.

3. The battery pack strength testing method as described in claim 1, characterized in that, The expression for the vibration frequency includes: ； （3） in, f i Indicates the vibration frequency, measured in Hz. i Represents the circumferential angular frequency, measured in Rad / s. i The order is a positive integer.

4. The battery pack strength testing method as described in claim 1, characterized in that, The stress expression includes: （4） Where, This represents the stress at the Gaussian integration point, in MPa. This represents the elastic coefficient matrix, in MPa, which is the usual elastic modulus. This represents the strain at the Gaussian integration point.

5. The battery pack strength testing method as described in claim 1, characterized in that, The method for dividing the battery pack structure into blocks to obtain static and dynamic modules includes: The battery pack is divided into multiple substructures according to its component structure; The substructures are combined according to the assembly process to obtain a static module; The remaining substructures are combined to form a dynamic module.

6. The battery pack strength testing method as described in claim 1, characterized in that, The method for determining the quality of the battery pack based on the strength includes: The obtained intensity is compared with a threshold; If the strength is greater than or equal to the threshold, the battery pack is of excellent quality, i.e., it meets the requirements; If the intensity is less than the threshold, the battery pack quality is poor, i.e., it does not meet the requirements.

7. A battery pack strength testing system, characterized in that, The system includes: A partitioning module is used to partition the structure of the battery pack to obtain static modules and dynamic modules; A data acquisition module is used to acquire assembly parameters between the static module and the dynamic module; A data processing module is used to input the assembly parameters into a pre-built computational model to obtain the strength of the battery pack. The method for constructing the computational model includes: The computational model is constructed based on the statics and dynamics equations, and the method includes: The vibration frequency expression and the stress expression are obtained by constructing the static equation and the dynamic equation; The computational model is obtained by combining the vibration frequency expression and the stress expression. A threshold is set for the judgment of the computational model; The static equations include: （1） Where, K oo This represents the internal stiffness matrix of the static module, in N / mm. K aa This represents the stiffness matrix at the connection between the static module and the dynamic module, in N / mm. K oa This represents the stiffness matrix at the coupling point between the internal and external parts of the static module, in N / mm. K oa T yes K oa The transpose matrix, in N / mm. u o The displacement of the static module represents its internal degrees of freedom, in mm. u a This indicates the displacement of the connection points, in mm. P This represents the load vector at the internal and connection points of the static module, in units of N; The kinetic equations include: （2） Where, M This represents the quality matrix of the static module, in units of t. C K represents the damping matrix, in mm / s / N, and K represents the static module stiffness matrix, in N / mm. This represents the acceleration vector, in mm / s². 2 , Represents the velocity vector, in mm / s. U This represents the displacement vector, in mm. A judgment module is used to judge the quality of the battery pack based on the intensity.

8. An electronic device, characterized in that: It includes a memory and a processor; the memory is used to store a computer program; the processor is used to implement the battery pack strength detection method as described in any one of claims 1 to 6 when the computer program is executed, or to implement the battery pack strength detection method as described in any one of claims 1 to 6 using the battery pack strength detection system as described in claim 7.

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