METHOD AND DEVICE FOR TESTING THE BATTERY CONDITION OF AT LEAST ONE BATTERY

Description

[0001] The invention relates to a method for testing a battery condition in at least one battery according to claim 1. A second aspect of the invention relates to a device for testing a battery condition in at least one battery according to claim 13.

[0002] Batteries, for example, for motor vehicles, can exhibit so-called battery defects even during production. The goal is therefore to detect these battery defects as early as possible and to sort out defective batteries.

[0003] The most common battery faults can affect the battery’s separator.

[0004] A battery separator is designed to spatially separate the cathode and anode in batteries, or the negative and positive electrodes in accumulators. The separator must act as a barrier that electrically isolates the two electrodes from each other to prevent internal short circuits. At the same time, however, the separator must be permeable to ions so that the electrochemical reactions in the cell can take place. A battery separator must be thin to keep internal resistance as low as possible and achieve a high packing density, thus enabling good performance and high capacities. Separators also serve to absorb the electrolyte and ensure gas exchange in sealed cells.

[0005] A typical battery failure is a damaged separator.

[0006] In the battery defect known as "short separator", there is a shortened separator, so that the geometrically complete contact area between the separator and the plate surface of the electrode is not covered.

[0007] Furthermore, unwanted so-called mass lumps can occur, which accumulate as contamination on the cathode or anode of the battery during production and thus significantly impair the battery's properties.

[0008] There may also be a bent electrode plate, which could lead to a short circuit in the battery.

[0009] Another common battery error is reverse polarity. This occurs when the electrodes were accidentally inserted backwards during battery manufacturing.

[0010] Battery defects can occur not only during battery production, but also during operation or use. Batteries are subject to numerous charging and discharging processes over the course of their service life. Added to this are the stresses caused by temperature fluctuations. These factors contribute to the occurrence of various types of unwanted battery errors or defects.

[0011] DE 10 2015 005 132 A1 discloses a method for testing a motor vehicle battery. In this method, the cell voltage of individual cells of the battery is determined and the determined cell voltage is automatically compared with a test parameter. This allows batteries replaced in vehicle workshops to be assessed for safety before being returned to the customer.

[0012] EP 1 037 063 A1 describes a detection device for fault detection in a battery pack, which device comprises a voltmeter and an ammeter. Fault detection is performed by determining the internal resistance of the battery pack.

[0013] DE 10 2013 013 471 A1 discloses a method for determining the supply line impedance in multi-cell battery packs for line fault detection. This method determines the presence of a line fault when the respective voltage differences at different cells within the battery pack have different signs.

[0014] This internal resistance, or impedance, of a battery is highly frequency-dependent. It decreases with increasing frequency and may contain reactive components. Therefore, it is also referred to as complex impedance and is represented either by magnitude and phase, for example, as a Bode diagram, or by real and imaginary parts, then as a locus curve.

[0015] The most comprehensive insight into battery behavior is provided by spectral impedance measurement, also known as electrical impedance spectrum (EIS). This allows the complex internal resistance to be measured at multiple frequencies, for example, from 0.1 Hz to 1 kHz, which can extend the measurement process to several minutes. The electrochemical behavior can be determined from the frequency response or locus curve. If the locus curve deviates significantly from the typical curve, for example, damage can be inferred.

[0016] For example, DE 10 2004 063 431 A1 also shows that the internal resistance of a battery is determined from a current-time integral of the current curve and from a voltage-time integral of a linearly decreasing voltage response.

[0017] As mentioned, this impedance spectroscopy (EIS) is used in a known manner in electrochemical systems, i.e., batteries, for example, lead-acid batteries, to analyze, characterize, and investigate the electrochemical properties of the system. In this measurement technique, a spectrum of a sinusoidal signal with a frequency range, for example, between µHz and MHz, is applied to the energy storage device, such as the battery, and the frequency response is analyzed.

[0018] Impedance reflects amplitude gain and phase shift. It is measured at various frequencies, ranging from several kilohertz down to the millihertz range, to capture the battery's impedance spectrum. Changes in battery behavior due to temperature, state of charge (SOC), or current load are reflected in correspondingly altered impedance curves.

[0019] EP 1 892 536 A1 also discloses monitoring the state of aging (SoH), state of charge (SoC), and degree of functional performance (SoF), for which impedance spectroscopy is performed. Impedance spectroscopy does not place a load on the battery, so the method is only suitable for determining the operating state, i.e., state of charge and state of aging. Both variables are calculated using the currently available capacity or the maximum capacity that can be drawn at full charge, respectively, at a low load current and at a defined temperature.

[0020] Based on this, DE 10 2016 216 664 A1 proposes a method for determining the functional reliability of a low-voltage battery of an at least partially electrically powered vehicle which is subjected to a test pulse, wherein the functional reliability of the battery is determined from a correlation of the voltage curve at the battery resulting during the test pulse with a predetermined functional requirement, wherein the functional reliability is given if the voltage curve of the battery during the test pulse satisfies several independent test criteria.

[0021] US 2017 / 350946 A1 and EP 2 778 697 A1 relate to a technique for monitoring a state of a storage battery to be effectively applied to a storage battery state monitoring system, as well as to a storage battery state monitoring method and a storage battery state monitoring program in which a state of a storage battery that is constantly connected to an apparatus for use in emergency power supply is monitored.

[0022] EP 1 115 171 A1 relates to a method for assessing the condition of a secondary battery, such as a nickel-hydrogen battery and a lithium secondary battery, in particular, a method for assessing initial activity and deterioration thereof. Furthermore, a method for regenerating a secondary battery, and in particular, a method for regenerating a nickel-hydrogen battery, is described.

[0023] The paper "Analysis of Advanced Lithium-Ion Batteries for Battery Energy Storage Systems" presented at the International Conference in Environment and Electrical Engineering (IEEE) 2018 describes various test methods for battery cells.

[0024] WO 2016 / 198 959 A2 relates to a device for determining the functional state of a battery.

[0025] US 5 193 067 A relates to a battery state detection device for accurately determining a state of charge, namely a capacity of a vehicle battery.

[0026] US 9 157 968 ​​B1 relates to rechargeable batteries and, in particular, to an improved system and method for characterizing the condition of a rechargeable battery.

[0027] CN 107 782 974 A relates to the field of measuring the internal resistance of a battery, in particular to a method and a device for online measuring the internal resistance of a lead-acid battery.

[0028] In the known methods, a single test is therefore first carried out to determine a battery fault in order to clearly identify multiple faults.

[0029] To precisely identify the battery fault(s), conventional methods first perform a single measurement on the battery. The battery is then quarantined for several weeks, for example, in a warehouse. Afterward, the battery is tested again to potentially detect any further faults.

[0030] This is disadvantageous because numerous batteries have to be stored for several weeks, which causes enormous storage costs.

[0031] Even with these known testing methods, it is only possible to detect up to three of the five most common faults. Two of the most common faults can only be detected after the battery has been delivered and after one to two years of operation.

[0032] This fault detection depends on the degree of fault exposure during the specified test time. A common test in battery manufacturing is the high-current test (HRD). However, this test can only identify faults that exhibit immediately different electrical measurements, such as a significantly defective cell or a broken cell bridge.

[0033] However, in order to be able to determine during quality control whether newly manufactured batteries have a defect that leads to a significant loss of voltage or capacity, the batteries must be stored in a "quarantine" so that a test for voltage or capacity loss can be carried out after a few weeks.

[0034] Also, with the known test methods, some of the battery faults may only become apparent after long-term mechanical or thermal stress on the battery or due to aging; for example, a bent plate could only lead to a short circuit after certain vibrations or aging (sulfation).

[0035] Another disadvantage of the known state of the art is that the functional performance of batteries can only be inadequately determined.

[0036] Based on the disadvantages described above, the object of the invention is to provide a method and a device of the type mentioned at the outset which enable a particularly early and accurate detection of a battery fault using simple means.

[0037] This object is achieved by a method for testing a battery condition in at least one battery according to claim 1. This object is also achieved by a device for testing a battery condition in at least one battery according to claim 13. Description of the invention

[0038] The invention relates to a method for testing a battery condition of at least one battery, in particular for determining a battery fault, comprising at least the following steps: Carrying out a first impedance test to determine the internal resistance of the battery, wherein the battery is loaded with an electrical current and a resulting voltage response of the battery is measured, recording and storing the measurement results of this first impedance test, carrying out a high-current load test of the battery with a test pulse or discharge pulse, preferably for a few seconds, carrying out a second impedance test, preferably after a pause of 1 to 10, in particular 2 seconds, recording and storing the measurement results of this second impedance test, evaluating the test by relating the measurement results of the first, the second impedance test and / or the high-current load test to one another, in particular by offsetting them against one another, in such a way that the battery condition can be derived therefrom, in particular whether a faulty battery is present.

[0039] In other words, an impedance test of the battery is performed first. This can take a few seconds. This is followed by a high-current load test, followed by another impedance test as a comparison measurement to the first impedance test.

[0040] The measurement results of the first impedance test are combined with those of the second impedance test, for example, by calculating them. Using this result and the high-current test, the defective batteries can then be filtered out and easily sorted out.

[0041] As mentioned, the internal resistance characterizes the ability of a battery to process a certain amount of energy before the voltage drops below a predefined limit, e.g. the cut-off voltage.

[0042] The total internal resistance of the battery consists of the ohmic resistance and the charge transfer resistance (CT), also called polarization resistance. The ohmic resistance represents the electrode resistance, electrolyte resistance, separator resistance, and contact resistance of each component and can be evaluated using electrochemical impedance analysis, known as ACR, at a single frequency.

[0043] To determine the charge transfer resistance of a battery, the battery can be discharged with two rapid pulses and the voltage drop can be assessed according to the discharged current. This process uses only the battery's direct current and is also known as a DCR test. This allows the total internal resistance of the battery to be obtained and the charge transfer resistance to be determined from it. These two test methods, ACR and DCR, offer the maximum ability to examine battery performance in a very limited test time, which is particularly advantageous on a production line because they do not increase cycle times.

[0044] During the high-current stress test, the battery is discharged with a relatively high current using a test pulse or discharge pulse, and the voltage is monitored during and after the test. This stress on the battery changes the battery's electrochemical properties. This change can be reflected in the ratio of faulty and fault-free batteries using impedance analysis.

[0045] The high-current stress test, also known as high-rate discharge (HRD), involves discharging the battery at high current. For example, the battery can be discharged at more than 10 times the so-called C-rate.

[0046] The C-rate describes the charge or discharge current of a battery, especially a rechargeable battery, relative to its capacity. It can be used, for example, to specify the maximum permissible charge and discharge currents, depending on the nominal capacity. The factor is also used conversely to specify the battery capacity as a function of the discharge current. The C-factor is defined as the quotient of this current and the capacity. For example, with a capacity of 70 Ah, 10 times the discharge current would correspond to a current of 700 A. The battery can be discharged with a constant current, constant voltage, or constant power.

[0047] In the high current load test, the open circuit voltage (OCV) and the load voltage at the end of the discharge pulse (constant current voltage, CCV) can be used to provide information about the battery condition.

[0048] The batteries tested can be, for example, so-called flooded lead-acid batteries or sealed batteries as well as lithium-ion batteries

[0049] According to the invention, the difference between the measurement results of the first and second impedance tests is calculated to determine whether this difference value lies outside a specified interval. Based on the difference values, it is determined whether an unacceptable deterioration of the battery condition is present or imminent. For example, the defective batteries can exhibit a deviation of 10% to 30%, in particular 20%, compared to fault-free batteries.

[0050] According to an advantageous further development of the invention, the high-current load test is performed for a duration of approximately 1 to 10 seconds, in particular for 3 seconds. This period is advantageous for ensuring battery quality and filtering out more defective batteries. A significantly longer test time, as known from the prior art, leads to slower production and a significant energy loss in the manufacturing process.

[0051] In a further advantageous variant of the invention, the measured values ​​of the individual measurements are correlated with one another in a freely configurable manner. By saving the measured values ​​of the individual process steps, they can be compared for different test profiles and used for further evaluations and statistical calculations. Depending on the battery type and capacity, the user can set specific test parameters such as current, voltage, test duration, pause time, and evaluation limit. The current measured values ​​can then be statistically compared with previous measurement data. For this purpose, the mean and standard deviation of the results can be determined and used, for example, to define an evaluation limit.

[0052] In an advantageous embodiment of the invention, several, in particular between three and five, individual test procedures are performed on a battery, and the results of the individual measurements are correlated with one another to then identify a faulty battery. For example, the test procedures of constant current discharge, constant voltage discharge, constant power discharge, DC internal resistance measurement, and AC impedance measurement can be performed consecutively in a test sequence, and the corresponding measurement results can be combined.

[0053] According to a further development of the invention, the first and / or second impedance test of the battery is carried out at a fixed frequency, in particular at a frequency of approximately 1 kHz. This measurement is also called a single-frequency measurement. The selected frequency depends on the battery type and the test time. For example, in lead-acid batteries, the impedance values ​​exhibit a stable real component and a small imaginary component from approximately 100 Hz to approximately 1 kHz. The single-frequency measurement has the advantage over a measurement using a frequency spectrum of shortening the test time while still obtaining a meaningful indication of the battery. The single-frequency method is also known as the ACR test, which represents the ohmic internal resistance of the battery, also called electrolyte resistance. In this case, the method can be carried out in just a few milliseconds.This makes it easy to use in so-called end-of-line test machines in production lines during battery manufacturing.

[0054] In a further development of the invention, the first and / or second impedance test of the battery is performed at multiple frequencies, in particular at approximately 0.5 Hz, 50 Hz, and 500 Hz. This offers the possibility of obtaining the optimal frequency range at which the measurement results are as meaningful as possible.

[0055] A further advantageous embodiment of the invention provides that the first and / or the second impedance test of the battery is carried out at a frequency spectrum, in particular at a frequency spectrum between 0.1 Hz and 1 MHz.

[0056] Fourier series can be used to calculate impedance. This allows the parameters of the battery's equivalent circuit to be identified by using a specific frequency range of the spectrum, for example, 0.1 Hz to 7.5 kHz for lead-acid batteries. For example, a so-called Nyquist diagram can be used to represent the impedance measurements as real and imaginary numbers using a Fourier transform to a complex number. To do this, the battery must be excited with a frequency spectrum of approximately 0.1 Hz to 7.5 kHz and the signal response measured. Using this diagram, the parameters of the equivalent circuit can be determined or read out. This parameterization contributes to a better investigation of the electrochemical properties of the batteries. In this way, faults in the battery can also be reflected through impedance analysis.

[0057] According to a further variant of the invention, the discharge pulse of the high-current stress test is maintained for a pulse duration of 1 to 10 seconds, preferably 2 to 4 seconds, in particular 3 seconds. This increases the production rate and reduces energy loss.

[0058] In the area of ​​lead-acid batteries, the test pulse or discharge pulse of the high-current load test can have a current of approximately 500 to 3000 amperes. The selected current depends on the battery capacity and can be determined depending on the battery manufacturer and the load duration. In principle, the C-rate of the battery applies here; for example, the battery can be loaded to a value between 1 and 20 times the C-rate. As mentioned, the C-rate describes the charging or discharging current of a battery, especially an accumulator, relative to its capacity. It can be used, for example, to specify the maximum permissible charging and discharging currents depending on the nominal capacity. For example, 15 times the C-rate of a 100 AH battery would correspond to a current of 1500 A.

[0059] Advantageously, the current intensity of the test pulse or discharge pulse of the high-current load test can be gradually increased. This allows the optimal load level for the respective battery design to be determined, allowing faults to be identified most effectively. Furthermore, unnecessary load on the battery is avoided.

[0060] It may also be planned to generate so-called discharge curves, i.e., the voltage and current during battery discharge, during the tests to precisely examine the battery's behavior under load. Battery discharge can be measured at constant current, constant voltage, or constant power, and the measurement results can be saved.

[0061] According to an independent aspect of the invention, a device for testing a battery state in at least one battery is provided, designed to carry out the method described above, which device has an impedance measuring device for carrying out at least a first and a second impedance test with determination of the internal resistance of the battery, wherein a high-current device is provided for carrying out a load high-current test of the battery with a test pulse or discharge pulse, and wherein the device has an evaluation unit for evaluating the tests.According to the invention, it is provided that the evaluation unit is designed to record and store the measurement results of the first and the second impedance test, in particular that the measurement results of the first and the second impedance test and / or the load high-current test are related to one another by means of the evaluation unit, in particular are offset against one another, in such a way that the battery condition can be derived therefrom, in particular whether a faulty battery is present.

[0062] Further objects, advantages, features, and possible applications of the present invention will become apparent from the following description of an exemplary embodiment with reference to the drawings. The subject matter of the present invention is defined in the claims.

[0063] Some of them are shown schematically: Figure 1 shows the sequence of a method for determining a battery state, Figure 2 shows a device for determining the battery state, and Figure 3 shows an exemplary diagram with measurement results.

[0064] In the following figures of the drawing, identical or equivalent components are provided with reference numerals based on an embodiment in order to improve readability.

[0065] Batteries 10, for example, for motor vehicles, can exhibit so-called battery defects even during production. The goal is therefore to detect these battery defects as early as possible and to sort out defective batteries 17.

[0066] As already mentioned above, one of the typical battery defects is a damaged separator. A "short separator" battery defect occurs when the separator is shortened, meaning that the geometrically complete contact area between the separator and the electrode plate surface is not covered.

[0067] Furthermore, unwanted so-called mass lumps or accumulations of material can occur, which accumulate as contamination on the cathode or anode of the battery during production and thus significantly impair the properties of the battery.

[0068] There may also be a bent electrode plate, which could lead to a short circuit in the battery.

[0069] Another common battery fault is reverse polarity. This occurs when the electrodes were accidentally inserted backwards during battery 10 manufacturing.

[0070] In order to be able to detect such errors already during the production of the batteries 10, so that defective batteries 17 can be sorted out directly, the invention proposes a method and device 11 for determining the battery condition.

[0071] In Figure 1A flowchart of a method for testing the battery condition of at least one battery 10, in particular for determining a battery fault, is shown, comprising at least the following steps: performing a first impedance test 1 with determination of the internal resistance of the battery 10, wherein the battery 10 is loaded with an electrical current at a specific frequency, and a resulting voltage response of the battery 10 is measured. Such a battery test can take a few seconds.

[0072] The measurement results of this first impedance test 1 are recorded and saved 5. These measured values ​​serve as reference values ​​for a subsequent, further impedance test.

[0073] Subsequently, a high-current load test 3 of the battery 10 is performed using a test pulse or discharge pulse. During the high-current load test 3, the battery 10 is discharged with a relatively high current using a test pulse or discharge pulse, and the voltage is monitored during and after the test. This load on the battery 10 changes its electrochemical properties. This change can be exploited by impedance analysis, as it reflects the ratio of faulty to fault-free batteries 10.

[0074] For example, battery 10 can be discharged at more than 10 times the so-called C-rate, where the C-rate describes the charging or discharging current of a battery, in particular a rechargeable battery, relative to its capacity. For example, with a capacity of 70 Ah, 10 times the discharge current would correspond to a current of 700 A. The battery can be discharged at a constant current, constant voltage, or constant power.

[0075] In the high current load test 3, the rest voltage and the load voltage at the end of the discharge pulse can be used to make a statement about the battery condition.

[0076] The tested batteries 10 can be, for example, so-called flooded lead-acid batteries or sealed batteries as well as lithium-ion batteries

[0077] Following this loading of the battery 10, a second impedance test 2 is carried out and its measurement results are also recorded and saved 6. This second impedance test 2 serves as a comparison measurement to the first impedance test 1.

[0078] The first 1 and / or the second impedance test 2 of the battery 10 can be performed at a fixed frequency, in particular at a frequency of approximately 1 kHz. This measurement is also called a single-frequency measurement. The selected frequency depends on the battery type and the permitted test time. For example, in the case of lead batteries, the impedance values ​​have a stable real component and a small imaginary component from approximately 100 Hz to approximately 1 kHz. However, it is also conceivable for the first 1 and / or the second impedance test 2 of the battery 10 to be performed at multiple frequencies, in particular at approximately 0.5 Hz, 50 Hz, and 500 Hz, or over a frequency spectrum, in particular a frequency spectrum between 0.1 Hz and 1 MHz.

[0079] Essential to the invention is the evaluation 7 of these tests, ie the impedance tests 1, 2 with the high-current load test 3 carried out in between. The measurement results of the first 1 and the second impedance test 2 and / or the high-current load test 3 are related to one another in an evaluation unit 16, in particular offset against one another, in such a way that the battery condition can be derived therefrom, in particular whether a faulty battery 17 is present.

[0080] In this example, the difference 8 between the measurement result of the first 1 and the second impedance test 2 is calculated to determine whether this difference value 8 lies outside a specified interval 9. Based on the difference values ​​8, it is determined whether an unacceptable deterioration of the battery condition is present or imminent. For example, the faulty batteries 10 can exhibit a deviation of 10% to 30%, in particular 20%, compared to fault-free batteries 10.

[0081] The result of such a test is in Figure 3 Here, the number of tested batteries (4) is plotted on the x-axis, meaning that each tested battery (10) is assigned a unique number with a corresponding measurement point. In this case, 26 batteries (10) were tested.

[0082] The y-axis shows the difference 8 between the measured values ​​from the first 1 and the second impedance measurement 2. In the present embodiment, this range is between 0.09 and 0.17.

[0083] Again Figure 3 As can be seen further, a limit 9 of 0.13 was specified for the difference 8 between the impedance measurements 1 and 2. It would also be conceivable to specify a specific interval 9.

[0084] The batteries 10 with the assigned numbers 1 to 21 all have a difference value of 8 that is below the limit of 9. In contrast, the difference values ​​8 for the batteries 10 with the numbers 22 to 26 are significantly above this limit of 9. These batteries 10 are defective batteries 17, i.e., those with a battery fault.

[0085] Figure 2shows a device 11 for testing a battery condition of at least one battery 10, in particular for carrying out the method described above, which device has an impedance measuring device 12 for carrying out at least a first 1 and a second impedance test 2 with determination of the internal resistance of the battery 10.

[0086] Of course, it is also conceivable within the meaning of the invention to carry out more than two impedance tests 1, 2 and several high-current load tests 3 and to combine the individual measurement results accordingly.

[0087] Furthermore, a high-current device 13 is provided for carrying out and measuring a high-current load test 3 of the battery 10 with a test pulse or discharge pulse.

[0088] Reference numeral 15 denotes measuring contacts, in particular four-pole measuring contacts for impedance measurements. Connected to these contacts are current clamps 14, which can be designed, in particular, as current clamps.

[0089] Furthermore, the device 11 has an evaluation unit 16 for evaluating the tests 7. The evaluation unit 16 is designed to record and store the measurement results 5 of the first impedance test 1, the second impedance test 2, and / or the high-current test 3.

[0090] The evaluation unit 16 can be a programmable logic controller (PLC), which is used to control or regulate the device 11 and is programmed digitally. In the simplest case, a PLC has inputs, outputs, an operating system (firmware), and an interface through which the user program can be loaded. The user program determines how the outputs are to be switched depending on the inputs. Furthermore, the evaluation unit 16 in the present embodiment is designed to analyze the measured values ​​of the impedance tests and output the measurement results.

[0091] Within the meaning of the invention, it is also conceivable that several, in particular between 3 and 5 individual test methods are carried out on a battery 10 and the results of the individual measurement results are correlated with one another in order to then identify a faulty battery 17. For example, the test methods of discharging the battery 10 at constant current (constant current discharge), discharging at constant voltage (constant voltage discharge), discharging at constant power (constant power discharge), measuring the DC internal resistance (DC internal resistance) and measuring the AC impedance can be carried out one after the other in a test sequence and the corresponding measurement results can be combined with one another. List of reference symbols

[0092] 1First impedance test 2Second impedance test 3High-current load test 4Number of batteries tested 5Recording and storing the measurement results 6Recording and storing the measurement results 7Evaluation of the tests 8Difference 9Specified interval or limit 10Battery 11Device 12Impedance measuring device 13High-current device 14Current clamps 15Measuring contacts for the impedance measurement 16Evaluation unit 17Defective battery

Claims

1. Method for testing a battery state of at least one battery (10), in particular for the identification of a battery defect, comprising at least the following steps: Execution of a first impedance test (1) for determining the internal resistance of the battery (10), wherein the battery (10) is excited by means of an electric current characteristic at a specific frequency, and a resulting voltage response of the battery (10) is measured; Capture and saving of the measurement results (5) of this first impedance test (1); Execution of a high-rate discharge test (3) of the battery (10) by the application of a test pulse or discharge pulse; Execution of a second impedance test (2); Capture and saving of the measurement results (6) of this second impedance test (2); Test evaluation (7), wherein the measurement results of the first (1) and the second impedance test (2) are considered in relation to one another, such that the battery state can be inferred therefrom; wherein a differential (8) is formed between the measurement result of the first (1) and the second impedance test (2), in order to infer herefrom whether this differential value (8) lies outside a stipulated limit (9) or a stipulated interval (9).

2. Method according to Claim 1, characterized in that the high-rate discharge test (3) is executed for a duration of approximately 1 to 10 seconds, in particular for 3 seconds.

3. Method according to one of the preceding claims, characterized in that measured values from individual measurements, in particular from the first (1) and second impedance test (2) and / or from the high-rate discharge test (3), are considered in relation to one another in a freely configurable manner.

4. Method according to one of the preceding claims, characterized in that multiple, in particular between 3 and 5 individual test procedures are executed on a battery (10), and that the outcomes of individual measurement results are considered in relation to one another, in order to identify a defective battery (10).

5. Method according to Claim 4, characterized in that test procedures executed on the battery (10) are constant current discharge of the battery (10), constant voltage discharge, constant power discharge, DC internal resistance measurement and AC impedance measurement wherein, in particular, a number or all of these test procedures are sequentially executed in a test sequence, and the corresponding measurement results are mutually combined.

6. Method according to one of the preceding claims, characterized in that the first (1) and / or the second impedance test (2) of the battery (10) is / are executed at a fixed frequency, in particular at a frequency of approximately 1 kHz.

7. Method according to one of the preceding claims, characterized in that the first (1) and / or the second impedance test (2) of the battery (10) is / are executed at multiple frequencies, in particular at approximately 0.5 Hz, 50 Hz and 500 Hz.

8. Method according to one of the preceding claims, characterized in that the first (1) and / or second impedance test (2) of the battery (10) is / are executed over a frequency spectrum, in particular over a frequency spectrum between 0.1 Hz and 1 MHz.

9. Method according to one of the preceding claims, characterized in that the test pulse in the high-rate discharge test (3) is sustained for a pulse duration of 1 to 10 seconds, preferably of 2 to 4 seconds, and in particular of 3 seconds.

10. Method according to one of the preceding claims, characterized in that the test pulse in the high-rate discharge test (3) assumes a current strength of approximately 500 to 3000 amperes, or in that the test pulse of the high-rate discharge test (3) assumes a current strength which corresponds to an approximate value of between 1 and 20 times the C-rate of the battery (10).

11. Method according to one of the preceding claims, characterized in that the current strength of the test pulse in the high-rate discharge test (3) is increased in a stepwise manner.

12. Method according to one of the preceding claims, characterized in that discharging of the battery (10) is measured at a constant current, or at a constant voltage, or at a constant power, and the measurement results are saved.

13. Device (11) for testing a battery state of at least one battery (10) which is designed to execute a method according to the preceding claims, and which comprises an impedance measuring device (12) for executing at least one first (1) and one second impedance test (2) for determining the internal resistance of the battery (10), wherein a high-current device (13) for executing a high-rate discharge test (3) of the battery (10) by means of a test pulse or discharge pulse is provided, and wherein the device (11) comprises an evaluation unit (16) for the evaluation (7) of tests, wherein the evaluation unit (16) is designed to capture and save measurement results (5) of the first (1) and second impedance tests (2), wherein, by means of the evaluation unit (16), measurement results of the first (1) and second impedance tests (2) are considered in relation to one another, such that the battery state can be inferred therefrom.