Method and device for determining a charge-state-dependent open-circuit voltage profile of a vehicle battery

Abstract

Method for determining a charge-state-dependent open-circuit voltage profile (3) of a vehicle battery in a vehicle, comprising: - a complete discharge (S1) of the vehicle battery by in-vehicle consumers, - a detection (S2) of a first detected charge-state-dependent voltage curve (1) during the discharge (S1) of the vehicle battery, - a complete charging (S3) of the vehicle battery by a charger, - a recording (S4) of a second recorded charge-state-dependent voltage curve (2) during the charging (S3) of the vehicle battery and - Determining (S5) the charge-state-dependent open-circuit voltage profile (3) by means of a weighted interpolation of the first recorded voltage profile (1) and the second recorded voltage profile (2).

Description

State of the art

[0001] The present invention relates to a method and a device, in particular a battery management system, for determining a charge state-dependent open circuit voltage curve of a vehicle battery in a vehicle.

[0002] Vehicle batteries for automotive applications are subject to aging, which changes the chemical and electrical properties of the vehicle battery. This decreases capacity and energy content, while the internal resistance generally increases.

[0003] In particular, the open-circuit voltage of the vehicle battery is subject to aging and, in some vehicle batteries, changes its state-of-charge-dependent profile. This impacts various algorithms executed by a responsible battery management system, such as the determination of the state of charge and the determination of capacity. Furthermore, the accuracy of the algorithms executed by the responsible battery management system is reduced.

[0004] The open-circuit voltage can be measured using the GITT method (Galvanostatic Intermittent Titration Technique). This involves discharging and charging a battery with a constant current. This measurement is preferably performed at the lowest possible current amplitude. The current amplitude can be selected, for example, according to a C-factor of C20. This means that the current amplitude is selected such that discharging a fully charged battery takes 20 hours. This increases the precision of the measurement with increasing measurement time.

[0005] The document DE 10 2007 031 305 A1 discloses a method for determining the open-circuit voltage of an electrochemical energy storage device, in which the open-circuit voltage is determined by means of an extrapolation method taking into account temperature-, current- and charge-compensated voltage values. Disclosure of the invention

[0006] The method according to the invention for determining a state-of-charge-dependent open-circuit voltage curve of a vehicle battery in a vehicle comprises a complete discharging of the vehicle battery by internal consumers of the vehicle, a recording of a first recorded state-of-charge-dependent voltage curve during the discharging of the vehicle battery, a complete charging of the vehicle battery by a charger, a recording of a second recorded state-of-charge-dependent voltage curve during the charging of the vehicle battery and a determination of the state-of-charge-dependent open-circuit voltage curve by means of a weighted interpolation of the first recorded voltage curve and the second recorded voltage curve.

[0007] The battery management system according to the invention is suitable for determining a state-of-charge-dependent open-circuit voltage curve of a vehicle battery in a vehicle. The battery management system comprises a discharging unit configured to fully discharge a vehicle battery using internal consumers of the vehicle, a charging unit configured to fully charge the vehicle battery using a charger, a detection unit configured to detect a first detected state-of-charge-dependent voltage curve during discharging of the vehicle battery and a second detected state-of-charge-dependent voltage curve during charging of the vehicle battery, and a determination unit configured to determine a state-of-charge-dependent open-circuit voltage curve by means of a weighted interpolation of the first detected voltage curve and the second detected voltage curve.

[0008] The method according to the invention and the battery management system according to the invention are advantageous because no additional hardware other than that otherwise required in user operation, nor any specialized personnel, is required to regularly determine the state-of-charge-dependent open-circuit voltage curve of a vehicle battery. Weighted interpolation achieves a particularly precise determination of the state-of-charge-dependent open-circuit voltage curve, whereby the results of algorithms based on it also lead to improved calculation results. Error influences, such as those caused by unequal charging and discharging currents, can be compensated for.

[0009] The subclaims show preferred developments of the invention.

[0010] Preferably, a first decision parameter is queried in an initial method step, and a decision as to whether the method should be continued is made based on a comparison of the first decision parameter with a given threshold value. The first decision parameter is, in particular, a parameter that describes a vehicle's mileage, a charge throughput of the vehicle battery, and / or an energy throughput of the vehicle battery. In this way, the method is executed when it is likely that a state-of-charge-dependent open-circuit voltage curve determined at an earlier point in time no longer corresponds to the actual state-of-charge-dependent open-circuit voltage curve. Constant, time-consuming measurements are thus avoided.

[0011] Likewise, before the method step of completely discharging the vehicle battery, a connection status query is preferably performed, which describes the availability of a charging voltage for charging the vehicle battery. The method is only continued when a charging voltage is available. This ensures that the method can be carried out completely and that the vehicle battery is only discharged when it can also be recharged. A charging voltage is always available at least when the vehicle is connected to a power supply. Since the vehicle is connected by a user, it is to be expected that the vehicle will not be needed at this time.

[0012] It is advantageous if, prior to the method step of completely discharging the vehicle battery, a query for a second decision parameter is performed. Input of the second decision parameter is preferably enabled by a user, and the method is terminated or continued depending on the second decision parameter. This ensures that a user has the option of aborting the method before discharging the vehicle battery. This prevents the vehicle from being in an inoperative state when the user wishes to use it.

[0013] Furthermore, it is advantageous if, before the method step of completely discharging the vehicle battery, a delay time is requested, wherein input of the delay time is preferably enabled by a user, and wherein, in a step following the delay time query, the method is delayed for the duration of the specified delay time if the delay time is not equal to zero. This allows the discharge of the vehicle battery to be postponed to a later time. Input of this delay time by the user is advantageous because it allows an estimate to be made of when the vehicle is not needed.

[0014] In particular, before the method step of complete discharging, a query about an execution duration is carried out, wherein an input of the execution duration is preferably made possible by a user, and wherein a battery current flowing during discharging of the vehicle battery and / or during charging of the vehicle battery is selected such that the method is completed within the specified execution duration. With a short execution duration, the vehicle is ready for use again sooner. With a long execution duration, more precise values ​​can be determined for the charge state-dependent idle voltage curve. The input of this execution duration by the user is advantageous because it allows an estimate to be made as to when the vehicle will be needed again and thus the input of a corresponding execution duration is possible.

[0015] In a preferred embodiment, prior to the method step of completely discharging the vehicle battery, a pre-charge of the vehicle battery is performed, during which the vehicle battery is fully charged. This ensures that a first recorded state-of-charge-dependent voltage curve can be determined across all charge states. The result of the determination is thus more precise, since no charge states occur for which only a second recorded state-of-charge-dependent voltage curve is recorded.

[0016] In particular, in the preferred embodiment described above, it is advantageous if a third detected state-of-charge-dependent voltage curve of the vehicle battery is detected during precharging. In this case, the state-of-charge-dependent open-circuit voltage curve is determined by means of a weighted interpolation of the first detected state-of-charge-dependent voltage curve, the second detected state-of-charge-dependent voltage curve, and the third detected state-of-charge-dependent voltage curve. The additionally detected third state-of-charge-dependent voltage curve achieves a more precise determination result based on additional measured values. This is particularly the case if only two detected state-of-charge-dependent voltage curves are available for determination in individual areas.In this case, the determination can also be made based on the remaining recorded charge state-dependent voltage curves.

[0017] In all embodiments, it is advantageous to maintain the temperature of the vehicle battery above a temperature threshold during charging and discharging of the vehicle battery, and in particular to maintain the temperature at a constant value above the temperature threshold. This is advantageous because temperature fluctuations can distort the recorded state-of-charge-dependent voltage curves. Advantageously, the temperature is adjusted by thermal management of the vehicle battery.

[0018] Furthermore, it is advantageous in all embodiments if a resulting charge-state-dependent open-circuit voltage curve is calculated by means of a weighted interpolation of the charge-state-dependent open-circuit voltage curve with a charge-state-dependent open-circuit voltage curve determined at an earlier point in time. Such interpolation compensates for any measurement errors and inaccuracies that may occur only during a single determination of a charge-state-dependent open-circuit voltage curve. However, repeatedly occurring characteristics are increasingly incorporated into the determination result. Short description of the drawings

[0019] Embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawing: Fig. 1 a flowchart of the method according to the invention in a first embodiment, Fig. 2 a flowchart of the method according to the invention in a second embodiment, and Fig. 3 a graphical representation of a charge state-dependent open circuit voltage curve, a first detected charge state-dependent voltage curve and a second detected charge state-dependent voltage curve. Embodiments of the invention

[0020] The method according to the invention enables the measurement or determination of a state-of-charge-dependent open-circuit voltage curve 3 of a vehicle battery. Thus, a change in this open-circuit voltage curve over the aging of the vehicle battery can also be detected. The method can be used in particular for determining the state-of-charge-dependent open-circuit voltage curve 3 in plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and electric vehicles (EVs). No hardware other than that already available is required. In particular, no special workshop tester is required. The determination of a state-of-charge-dependent open-circuit voltage curve 3 is essentially carried out according to the GITT method.

[0021] In the method according to the invention, the charge state-dependent idle voltage curve 3 is determined internally in the vehicle, as precisely as possible and only with hardware available in the vehicle.

[0022] The Fig. Figure 1 shows a flowchart of the method according to the invention in a first embodiment. The method can be initiated, for example, by a start signal from an independent vehicle system or by a user request.

[0023] In a first process step S1, the vehicle battery is completely discharged by the vehicle's internal consumers. Internal consumers are those vehicle components that are also available when the vehicle is in use. Examples of such components include a heater (possibly compensated by simultaneous operation of a cooling system), fans, pumps, electric motors, or similar components. Preference should be given to consumers characterized by constant power consumption.

[0024] When completely discharging the vehicle battery by the vehicle's internal consumers in the first process step S1, it is advantageous if the discharge is carried out with as constant a discharge current as possible. An external or internal charger is also considered an internal consumer if it has the ability to feed power back into the power grid.

[0025] During the discharging of the vehicle battery in the first method step S1, a first detected charge-state-dependent voltage curve 1 is recorded in a second method step S2, which is carried out simultaneously. This recording can be carried out, for example, by a time-clocked measurement of voltage values ​​at the terminals of the vehicle battery. Each voltage value recorded is assigned to a charge state of the vehicle battery. The charge state could, for example, be described by the time that elapses between the measurement of a voltage value and a complete discharge of the vehicle battery. Such a first detected charge-state-dependent voltage curve 1 is shown in Fig. 3 shown.

[0026] In a third process step S3, the vehicle battery is fully charged by a charger. This charging is carried out with a charging current that is as constant and low as possible. Charging can be performed via a connected external or internal charger. Charging is also possible via an in-vehicle generator, powered, for example, by an internal combustion engine or another energy source. Charging via a second vehicle battery with an interposed DC / DC converter is also possible.

[0027] The discharge current occurring in the first method step S1 and the charging current occurring in the third method step S3 preferably have the same current amplitude.

[0028] During charging of the vehicle battery in the third method step S3, a second detected charge state-dependent voltage curve 2 is recorded in a fourth method step S4, which is carried out simultaneously. This recording can be carried out, for example, by a time-clocked measurement of voltage values ​​at the terminals of the vehicle battery. Each voltage value recorded is assigned to a charge state of the vehicle battery. The charge state could, for example, be described by the time that elapses between the measurement of a voltage value and a full charge of the vehicle battery. Such a second detected charge state-dependent voltage curve 2 is shown in Fig. 3 shown.

[0029] It is advantageous to perform a rest period with zero current after the end of discharging in the first method step S1 and / or charging in the third method step S3 to increase the precision of the measurements. A rest period of between one and five hours is advantageous, as this allows the vehicle battery to cool down.

[0030] In a fifth method step S5, the state-of-charge-dependent open-circuit voltage curve 3 is determined by means of a weighted interpolation of the first detected voltage curve 1 and the second detected voltage curve 2. For this purpose, an average value is calculated from each voltage value recorded in the second method step S2 and the voltage value recorded for the same state of charge in the fourth method step. This averaging can be weighted if the impedance of the battery differs in the charging and discharging directions. Weighting means that either the voltage values ​​recorded in the second method step S2 or the voltage values ​​recorded in the fourth method step are weighted by a factor during averaging. Likewise, compensation for the state-of-charge dependence of charging and discharging impedance can advantageously be carried out, particularly if this dependence differs in the charging and discharging directions.Furthermore, weighting is advantageous if the same current amplitude cannot be achieved for charging and discharging. In this case, it is particularly advantageous to select a weighting based on the ratio of the current amplitudes of the charging current and the discharging current. If necessary, this weighting can be corrected according to a different impedance in the charging and discharging directions. The charge-state-dependent open-circuit voltage curve 3 results from the calculated mean values. A charge-state-dependent open-circuit voltage curve 3 determined by averaging is shown in . Fig. 3 shown.

[0031] Depending on the state of charge of the vehicle battery at a time when the first method step S1 is carried out and the vehicle battery is thus discharged, a voltage value cannot be recorded for every possible state of charge. Thus, the first recorded state-of-charge-dependent voltage curve 1 does not always cover all possible states of charge of the vehicle battery. It is therefore advantageous to carry out the first and second method steps S1, S2 when the vehicle battery has a high state of charge. In the event that the first recorded state-of-charge-dependent voltage curve 1 does not cover all possible states of charge of the vehicle battery, an estimate or extrapolation of the unavailable voltage values ​​can be made. This reduces the precision of the result of determining the state-of-charge-dependent open-circuit voltage curve 3. However, the time required is shortened.

[0032] In an alternative embodiment of the invention, the vehicle battery is pre-charged before it is fully discharged in the first method step S1. The vehicle battery is first fully charged. This method step is particularly advantageous if the vehicle battery has a low state of charge before the start of the first method step S1. The pre-charge is either always carried out before the first method step S1 of fully discharging the vehicle battery, or is only carried out if the state of charge of the vehicle battery is below a given value. In such an embodiment, a high level of precision is achieved in determining the state of charge-dependent open circuit voltage curve 3, since voltage values ​​of the first detected state of charge-dependent voltage curve 1 are detected for each state of charge of the battery.

[0033] In such an alternative embodiment, it is also advantageous if a third detected state-of-charge-dependent voltage curve is recorded during precharging of the vehicle battery. Thus, additional measured voltage values ​​are available for an even more precise determination of the state-of-charge-dependent open-circuit voltage curve 3. In this case, the state-of-charge-dependent open-circuit voltage curve 3 is determined by means of a weighted interpolation of the first detected state-of-charge-dependent voltage curve 1, the second detected state-of-charge-dependent voltage curve 2, and the third detected state-of-charge-dependent voltage curve.

[0034] The Fig. 2 shows a flowchart of the method according to the invention in a second embodiment. The method is carried out by a battery management system of a vehicle. To determine a state-of-charge-dependent open-circuit voltage curve 3 of a vehicle battery, the first to fifth method steps described in the first embodiment are applied. This means that the vehicle battery is completely discharged, the first detected state-of-charge-dependent voltage curve is detected, the vehicle battery is completely charged, the second detected state-of-charge-dependent voltage curve is detected, and the state-of-charge-dependent open-circuit voltage curve is determined. Optionally, the vehicle battery can also be precharged and, in particular, the third state-of-charge-dependent voltage curve is determined prior to the first method step.The process is initiated when a user puts the vehicle into operation.

[0035] In this second embodiment, however, a first decision parameter p1 is queried in an initial method step S6. The first decision parameter p1 can be provided by other systems in the vehicle or by the battery management system itself. Examples of the first decision parameter p1 are a current date, a vehicle's mileage, a charge throughput of the vehicle battery, or an energy throughput of the vehicle battery. The queried first decision parameter p1 is compared with a predetermined threshold value x in method step S6'. This threshold value x can be specified in the battery management system during a manufacturer or user configuration. If the obtained decision parameter p1 is greater than the threshold value x, the method continues.If the related decision parameter p1 is smaller than the threshold value x, the method branches back to the initial method step S6, which is then executed again.

[0036] In the second embodiment described here, the first decision parameter p1 is the vehicle's mileage. The threshold value x is specified by the manufacturer of the battery management system with a value of 5,000 km. At the beginning of the method, the vehicle's mileage is therefore queried from a vehicle odometer. The decision parameter p1 obtained in this way is compared with the threshold value x = 5,000 km in a subsequent comparative method step S6'. If the obtained decision parameter p1 is greater than the threshold value x, i.e. p1 > x (= 5,000 km), the method is continued. If the obtained decision parameter p1 is less than the threshold value x, i.e. p1 ≤ x (= 5,000 km), the method branches back to the introductory method step S6, which is then executed again.In this example, the charge state-dependent idle voltage curve is determined after the vehicle has driven 5,000 km.

[0037] It is also possible to specify multiple threshold values ​​and thus define intervals. Fig. In the embodiment shown in Figure 2, the threshold value x is redefined in a final method step S11, which occurs after determining the state-of-charge-dependent open-circuit voltage curve in the fifth method step S5. For this purpose, a given value can be added to the previous threshold value, for example.

[0038] Since vehicle battery aging is a relatively slow process, it is necessary to determine the state-of-charge-dependent open-circuit voltage curve 3 at longer intervals. The determination may be necessary, for example, after a certain period of time (e.g., every 3 months), after a certain mileage (e.g., every 5,000 km), after a certain charge throughput (e.g., every 2 mAh), or after a certain energy throughput (e.g., every 1 MWh).

[0039] As previously described, the method continues if the related decision parameter p1 is greater than the threshold value x. In this case, after the comparative method step S6', a query for a connection status v takes place in a querying method step S7. The connection status v describes the availability of a charging voltage for charging the vehicle battery. If a charging voltage is available, the connection status v is positive. If no charging voltage is available, the connection status v is negative. The connection status v could, for example, be recorded by a sensor that detects a voltage at contacts used to connect a charging cable to the vehicle. If the charging voltage detected at the contacts exceeds a given threshold value, the connection status v is positive. Such a sensor can, for example, be provided by charging electronics.In a further comparative step S7', an evaluation is performed to determine whether the connection status v is positive or negative. If the queried connection status v is positive, the process continues. If the queried connection status is negative, the process branches back to the querying step S7, where the connection status query is executed again.

[0040] Since discharging and charging the vehicle battery in the first and third method steps S1, S3 can take several hours, a user should have the option of postponing discharging in the first method step S1 and charging the vehicle battery in the third method step S3 if the vehicle is needed promptly. Therefore, in a subsequent method step S8, which is carried out after the further comparative method step S7', if the connection status queried in the querying method step S7 is positive, a second decision parameter p2 is queried. The decision parameter p2 is preferably defined by a user input. For example, a message could be generated on a display inside the vehicle requesting the user's consent to continue carrying out the method. The second decision parameter p2 is set depending on a user input.The second decision parameter p2 is set to "1" if the user wishes to determine the state-of-charge-dependent open-circuit voltage curve, and the second decision parameter p2 is set to "0" if the user does not wish this at that time, for example because the vehicle will be needed again in a short time. The method is terminated or continued depending on the second decision parameter p2. Since completing the method, in particular discharging and charging the vehicle battery in the first and third method steps S1, S3, requires a considerable amount of time for the user, the user is given the option of aborting the method. This ensures that the vehicle is in an operational state when the user so wishes.In a first checking process step S8', a check is made to determine whether the requested second decision parameter p2 is equal to "1." If this is not the case (if the second decision parameter p2 was set to "0"), the process is terminated. In this case, the determination of a state-of-charge-dependent open-circuit voltage curve can only be achieved after the process is initiated again. If the requested second decision parameter p2 is equal to "1," the process continues.

[0041] In a further subsequent method step S9, which in this embodiment is combined with the following method step S8 in which the second decision parameter p2 is queried, a delay time t is queried. The delay time t is defined by an input from the user. For example, a message could be generated on the display inside the vehicle prompting the user to define a period of time after which the first method step S1 will be executed at the earliest if immediate execution is not desired. In a second checking method step S9', a check is made to determine whether the delay time t was selected to be "0". If a delay time t other than "0" is selected by the user, the method is delayed in a delay step S10 for the duration of this delay time t.Following this delay, the method is resumed at the point of the querying method step S7. This is advantageous because the vehicle may no longer be supplied with a charging voltage when the delay time t expires. If a delay time t equal to "0" is selected, i.e., no delay, the first method step, i.e., discharging the vehicle battery, is carried out immediately. In this case, the method is carried out further with all steps according to the first embodiment. Before the method is concluded, the previously described concluding method step S11 is carried out.

[0042] In a further alternative embodiment, which can be combined with the embodiments already described, a query about an execution duration takes place in the first method step S1 before the vehicle battery is completely discharged. The execution duration is preferably defined by a user input. For example, a message could be generated on a display inside the vehicle offering the user several execution durations to choose from. A choice could be given between a quick measurement (e.g. 8 hours execution duration), a standard measurement (e.g. 24 hours execution duration), and a precision measurement (e.g. 48 hours execution duration). The execution durations can be freely selected or adapted to the physical properties of the vehicle battery. The charge state of the vehicle battery at the time of selection also plays a role.The execution times can therefore be variable and can be offered for selection according to the current charge state of the vehicle battery.

[0043] Subsequently, the discharge current and the charge current are adjusted such that the method is completed within the execution time preferably selected by the user. For a long execution time (e.g., 48 hours), a lower discharge current and / or charge current is selected than for a short execution time (e.g., 8 hours). Since a lower charging and / or discharging current flows during a long execution time, the battery heats up less, and the first recorded state-of-charge-dependent voltage curve 1 and the second recorded state-of-charge-dependent voltage curve 2 are less distorted by thermal influences. The precision in determining the state-of-charge-dependent open-circuit voltage curve 3 increases.

[0044] Since the results are comparatively imprecise at very short run times (e.g., 8 hours for the quick measurement described above), the result cannot always be used directly. Therefore, weighting with the current state-of-charge-dependent open-circuit voltage curve at that time is advantageous.

[0045] Therefore, the method according to the invention can comprise a calculation step in which a resulting charge-state-dependent open-circuit voltage curve is determined by means of a weighted interpolation of the charge-state-dependent open-circuit voltage curve 3 with a charge-state-dependent open-circuit voltage curve determined at an earlier point in time. For this purpose, for each voltage value of a charge-state-dependent open-circuit voltage curve 3, an average value is formed with a voltage value of a previously determined charge-state-dependent open-circuit voltage curve that was determined for a corresponding charge state. A weighted interpolation means that the voltage value of the charge-state-dependent open-circuit voltage curve determined at an earlier point in time is incorporated multiple times into the formation of the average value. For example, the charge-state-dependent open-circuit voltage curve determined at an earlier point in time couldbe weighted twice as much as the current state-of-charge-dependent open-circuit voltage curve 3. The resulting state-of-charge-dependent open-circuit voltage curve is described by the mean values ​​determined in this way. Such interpolation can also reduce any measurement errors that may occur (provided they are not systematic). However, such interpolation may require more frequent determination of the state-of-charge-dependent open-circuit voltage curve.

[0046] Furthermore, it is advantageous to shorten the interval until the charge state-dependent open-circuit voltage curve 3 is determined again in the case of a short execution time.

[0047] In a further alternative embodiment, which can be combined with the embodiments already described, the temperature of the vehicle battery is kept above a temperature threshold during charging and discharging of the vehicle battery. This can be achieved by a controlled cooling and / or heating device. The temperature of the vehicle battery can also advantageously be adjusted by the thermal management of the vehicle battery. In this embodiment, the recorded state-of-charge-dependent voltage curves 1, 2 are recorded at room temperature or higher, as this reduces the influence or error caused by the battery's impedance. The temperature of the vehicle battery is kept as constant as possible by the provided means.

[0048] In all embodiments, a currently determined charge-state-dependent open-circuit voltage curve 3 can replace a previously determined charge-state-dependent open-circuit voltage curve. The same applies to a resulting charge-state-dependent open-circuit voltage curve.

[0049] In addition to the above written revelation, explicit reference is made to the revelation of Fig. 1 to 3.

Claims

[1] Method for determining a charge state-dependent open circuit voltage curve (3) of a vehicle battery in a vehicle, comprising: - a complete discharge (S1) of the vehicle battery by internal vehicle consumers, - detecting (S2) a first detected charge state-dependent voltage curve (1) during the discharging (S1) of the vehicle battery, - a full charge (S3) of the vehicle battery by a charger, - detecting (S4) a second detected charge state-dependent voltage curve (2) during charging (S3) of the vehicle battery and - Determining (S5) the charge state-dependent open-circuit voltage curve (3) by means of a weighted interpolation of the first detected voltage curve (1) and the second detected voltage curve (2). [2] Method according to claim 1, characterized byin that in an introductory method step (S6) a first decision parameter (p1) is queried and a decision as to whether the method is continued is made on the basis of a comparison of the first decision parameter (p1) with a given threshold value (x), wherein the first decision parameter (p1) is in particular a parameter which describes a time period, a km performance of the vehicle, a charge throughput of the vehicle battery and / or an energy throughput of the vehicle battery. [3] Method according to one of the preceding claims, characterized by that before the method step of completely discharging the vehicle battery, a query (S7) of a connection status is carried out which describes the availability of a charging voltage for charging the vehicle battery, and the method is not continued until a charging voltage is available. [4] Method according to claim 1, characterized bythat before the method step of completely discharging (S1) the vehicle battery, a query (S8) of a second decision parameter (p2) is carried out, wherein preferably an input of the second decision parameter (p2) by a user is enabled, and wherein the method is terminated or continued depending on the second decision parameter (p2). [5] Method according to one of the preceding claims, characterized by that before the method step of completely discharging (S1) the vehicle battery, a query (S9) of a delay time (t) is carried out, wherein preferably an input of the delay time (t) by a user is enabled, and wherein the method is delayed in a step (S10) following the query (S9) of the delay time for the duration of the specified delay time (t) if the delay time (t) is not equal to zero. [6] Method according to one of the preceding claims, characterized bythat before the method step of complete discharging (S1) a query of an execution time is carried out, wherein preferably an input of the execution time by a user is enabled, and wherein a battery current flowing during discharging of the vehicle battery and / or during charging of the vehicle battery is selected such that the method is completed within the predetermined execution time. [7] Method according to one of the preceding claims, characterized by that before the process step of completely discharging (S1) the vehicle battery, a pre-charging of the vehicle battery takes place in which the vehicle battery is fully charged, wherein in particular - a third recorded charge state-dependent voltage curve is recorded during the pre-charging of the vehicle battery, and - the determination (S3) of the charge state-dependent open-circuit voltage curve (3) is carried out by means of a weighted interpolation of the first detected charge state-dependent voltage curve (1), the second detected charge state-dependent voltage curve (2) and the third detected charge state-dependent voltage curve. [8] Method according to one of the preceding claims, characterized by that a temperature of the vehicle battery is kept above a temperature threshold during charging and discharging of the vehicle battery, and in particular the temperature is kept at a constant value above the temperature threshold. [9] Method according to one of the preceding claims, characterized bythat the method further comprises a calculation step in which a resulting charge state-dependent open-circuit voltage curve is calculated by means of a weighted interpolation of the charge state-dependent open-circuit voltage curve (3) with a charge state-dependent open-circuit voltage curve determined at an earlier point in time. [10] Battery management system suitable for determining a charge state-dependent open circuit voltage curve (3) of a vehicle battery in a vehicle, comprising: - a discharge unit designed to completely discharge a vehicle battery using the vehicle's internal consumers, - a charging unit designed to fully charge the vehicle battery using a charger, - a detection unit configured to detect a first detected charge state-dependent voltage curve (1) during discharging of the vehicle battery and a second detected charge state-dependent voltage curve (2) during charging of the vehicle battery, and - a determination unit which is configured to determine the charge state-dependent no-load voltage curve (3) by means of a weighted interpolation of the first detected voltage curve (1) and the second detected voltage curve (2).

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