METHOD FOR DETERMINING THE STATE OF HEALTH OF A BATTERY AND DEVICE FOR IMPLEMENTING THE METHOD

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of battery management. The present invention relates to a method for determining the state of health of a battery and in particular a determination method which makes it possible to determine said state of health from a partial charge or discharge of said battery. The invention also relates to a device for implementing said method. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Generally speaking, the state of health of a battery can only be accessed by means of a complete charge or discharge of said battery. However, when a battery is installed in a device, it is rarely possible to carry out a complete charge or a complete discharge as part of the normal operation of said device. In addition, this charge or discharge operation must be carried out under controlled conditions, in particular with regard to current, temperature and voltage thresholds. Thus, normal operation must be altered in order to access said state of health. In order to address this issue, alternative methods have been proposed to measure the state of health of a battery from partial charges or discharges.

[0003] In patent WO 2015049300 A1, the authors exploit the constant voltage end-of-charge phase of Li-Ion batteries. Parameters of the equation used to model the evolution of the current during this charging phase have a linear relationship with the state of health. Exploiting the end of charge in this case allows the state of health to be estimated. However, the proposed method has the disadvantage of requiring strict control of the current during a first charge (the latter must be constant) and of the voltage during a second charge (the latter must be equal to a determined limit value).

[0004] In patent WO2017 / 050944, the inventor exploits the evolution of the no-load voltage (under zero current) called OCV for Open Circuit Voltage, either after a discharge or after a charge, by establishing a relationship between OCV and the state of health. Partial charges or discharges are thus exploited to estimate the state of health.

[0005] In patent WO2015 / 086753, the inventors exploit a discharge voltage range (respectively charge), restricted compared to a full discharge (respectively full charge). The authors specify the method for defining this restricted range, so as to make it optimal and efficient for estimating the state of health from a cumulative Ah over this restricted range.

[0006] Document FR3051981 A1 discloses an alternative method for determining the state of health of a lithium battery composed of one or more cells connected together.

[0007] There is therefore a need for a method for determining the state of health of a battery from a partial charge or discharge without requiring strict control of the current or voltage during said charge or discharge. SUMMARY OF THE INVENTION

[0008] The invention provides a solution to the problems mentioned above, by making it possible to determine the state of health of a battery from a partial charge or discharge of said battery. The invention is defined by the independent method claims 1 and 3 as well as by the device of independent claim 6, the computer program of claim 7 and the computer-readable medium of claim 8. Optional embodiments are defined by dependent claims 2, 4 and 5.

[0009] A first aspect of the invention relates to a method for determining the state of health of a battery, called the overall state of health, the voltage at the terminals of the battery as a function of the state of charge being able to be split into a first phase, called phase A, and a second phase, called phase B, phase A and phase B being distinct and consecutive, phase A being associated with a first state of health and phase B being associated with a second state of health, the overall state of health being equal to the sum of the state of health associated with phase A and the state of health associated with phase B; the method being characterized in that the overall state of health of the battery is determined as a function of at least one measurement of the state of health associated with phase A and / or the state of health associated with phase B.

[0010] Thus, it is possible to determine, from a charge (respectively a partial discharge) according to one of the two phases (phase A or phase B) the overall state of health of a battery. In addition, no particular condition on the current and voltage during said partial charge (respectively discharge) is necessary to implement the method according to a first aspect of the invention.

[0011] In addition to the characteristics which have just been mentioned in the preceding paragraph, the method according to a first aspect of the invention may have one or more complementary characteristics among the following, considered individually or according to all technically possible combinations.

[0012] In one embodiment, the state of health (SOH Y ) associated with phase Y with Y = A or B is measured using the following equation: SOH Y = 100 × Q Dch _ Y k Q Dch _ Tot 0 where SOH Y is the state of health associated with phase Y, Q Dch- Y(k) is the quantity of Ah accumulated during a charge (respectively discharge) during phase Y in cycle k and Q Dch- Tot(0) is the quantity of Ah accumulated during a total charge (respectively discharge) in the first cycle.

[0013] In other words, the health status associated with phase A or phase B can be determined from the amount of Ah accumulated during a charge (respectively a discharge) during said phase, without condition as to the operating regime of the battery. The number of equivalent cycles is understood to be the number equal to the amount of Ah accumulated during charge (respectively during discharge) divided by the nominal capacity of the battery (or capacity specified by the battery manufacturer).

[0014] In one embodiment, the determination method according to the invention comprises, when the partial charge (respectively discharge) occurs in phase A: a step of measuring the state of health associated with phase A; if the state of health associated with phase B is zero, a step of determining the overall state of health of the battery, said overall state of health being equal to the state of health associated with phase A determined during the step of measuring the state of health associated with phase A; if the state of health associated with phase B is non-zero, a step of determining the overall state of health of the battery, said overall state of health being equal to the state of health associated with phase A determined during the step of measuring the state of health associated with phase A added to the state of health associated with phase B determined during a previous measurement.

[0015] In one embodiment, the determination method according to the invention comprises, when the partial charge (respectively discharge) occurs in phase B: a step of measuring the state of health associated with phase B; if the state of health associated with phase A is known, a step of determining the overall state of health of the battery, said overall state of health being equal to the state of health associated with phase A added to the state of health associated with phase B determined in the step of measuring the state of health associated with phase B; if the state of health associated with phase A is not known, a step of determining the overall state of health of the battery, said overall state of health being equal to the state of health associated with phase B measured in the step of measuring the state of health associated with phase B added to the initial state of health associated with phase A.

[0016] Thus, it is possible to determine the overall health status of the battery from the measurement of the health status associated with phase A or phase B, i.e. from a partial discharge carried out in phase A or in phase B.

[0017] According to independent claim 3, the health state associated with phase Y with Y = A or B can be modeled by the following equation: SOH Y = max A Y x + B Y , 0 where AX and BX are constants and x is a number of equivalent cycles and the method according to a first aspect of the invention comprises: a first phase, called the initialization phase and comprising: ▪ a step of at least four measurements of the overall state of health, each measurement being carried out on a complete charge (respectively a discharge); ▪ a step of determining the parameters of the models associated with the state of health associated with phase A and phase B; a second phase, called the measurement phase and comprising: ▪ a step of determining the number of equivalent cycles using a partial charge (respectively discharge) in phase A or phase B; ▪ a step of determining the overall state of health; the overall health status being obtained by adding the health status associated with phase A and the health status associated with phase B, the health status associated with each of phases A and B being determined from the model obtained during the initialization phase and the number of equivalent cycles obtained during the measurement phase.

[0018] Thus, it is possible to determine the parameters of the equation governing the evolution of the health state associated with phase A and the health state associated with phase B (and therefore the overall health state) as a function of the number of equivalent cycles. This also means that it is possible to know the number of equivalent cycles from which the health state associated with phase B is zero.

[0019] A second aspect of the invention relates to a device for determining the state of health of a battery comprising a means for measuring the current entering and leaving the battery as well as a calculation means connected to said measuring means and configured to implement a method according to a first aspect of the invention.

[0020] The device according to the invention makes it possible to determine the overall state of health of the battery from a partial charge or discharge without requiring strict control of the current or voltage during said charge or discharge.

[0021] A third aspect of the invention relates to a computer program comprising instructions which cause the device according to a second aspect of the invention to execute the steps of the method according to a first aspect of the invention.

[0022] A fourth aspect of the invention relates to a computer-readable medium, on which the computer program according to a third aspect of the invention is recorded.

[0023] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0024] The figures are presented for information purposes only and in no way limit the invention. There Figure 1 shows two curves illustrating the two phases in the charging and discharging of a battery. The Figure 2 shows the two periods in the evolution of the overall health of a battery. The Figure 3 shows a linear regression to determine the parameters of the overall health of a battery. The Figure 4 shows a flowchart of an embodiment of a method according to a first aspect of the invention. The Figure 5 shows a flowchart of an embodiment of a method according to a first aspect of the invention. The Figure 6 shows a schematic representation of a device according to a second aspect of the invention.

[0025] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0026] A first aspect of the invention relates to a method 10 for determining the state of health SOH Tot of a battery. In order to be able to implement the method 10 according to the invention, it is important that the state of health SOH Tot of the battery, called the overall state of health, can be split into a first state of health SOH A associated with a first phase of charging or discharging the battery, called phase A, and a second state of health SOH B associated with a second phase of charging or discharging the battery, called phase B. In other words, the characteristic of the voltage at the terminals of the battery as a function of the state of charge can be split into a first phase, called phase A, and a second phase, called phase B, phase A and phase B being distinct and consecutive, phase A being associated with a first state of health SOH A and phase B being associated with a second state of health SOH B.These two phases therefore correspond to consecutive partial charges (or discharges) so as to form a complete charge (or discharge). Thus, this characteristic can in particular be verified by measuring the voltage at the terminals of a battery as a function of the state of charge SOC of the latter. More particularly, the limit between phase A and phase B can be determined by identifying a threshold slope (voltage difference between two SOC values divided by the difference between the two SOC values) greater than a threshold value, for example greater than 50mV / %SOC, knowing that in general the slopes are less than 20mV / %SOC for the majority of the %SOC values (with the exception of the very end of discharge). The method according to a first aspect of the invention is particularly advantageous in the case of Na-lon batteries. Indeed, a Na-lon battery has these two phases A and B.However, the process can also be used for other battery types, e.g. Na-NiCl 2 batteries (high temperature batteries) and Li-lon batteries with mixed electrode materials.

[0027] Indeed, the inventors have shown that the evolution of the overall SOH Tot health status could be broken down into two contributions: a first contribution due to the evolution of the state of health SOH Tot during the charges and discharges of the battery in a first phase, called phase A in the following, this contribution being called state of health SOH A associated with phase A; a second contribution due to the evolution of the state of health SOH Tot during the charges and discharges of the battery in a second phase, called phase B in the following, this contribution being called state of health SOH B associated with phase B.

[0028] There Figure 1 illustrates the charge ( Figure 1A ) and the discharge ( Figure 1B) of a battery. More particularly, the two curves represent the voltage at the terminals of a battery as a function of the state of charge SOC in the case of a Na-Ion battery and in particular an organic Na-Ion battery. On these two curves, two phases can be easily delimited, the delimitation point being the point of inflection of the curve which generally occurs when the state of charge SOC is approximately equal to 30% of the state of charge SOC at full charge. Phase A within the meaning of the invention is the phase during which the state of charge SOC is between the maximum state of charge and the transition state of charge, i.e. the state of charge for which the inflection of the curve mentioned above occurs. Phase B of the invention concerns the phase during which the state of charge is between the transition state of charge and the minimum state of charge.

[0029] By associating a SOH A state of health with phase A and a SOH B state of health with phase B, the inventors were able to highlight two periods in the evolution of the overall SOH Tot state of health of the battery. These two periods are clearly visible on the Figure 2which represents the overall SOH Tot state of health of a battery based on a number of equivalent cycles. As a reminder, the number of equivalent cycles is understood to be the number equal to the quantity of Ah accumulated in charge (or discharge) divided by the nominal capacity of the battery (or capacity specified by the battery manufacturer). During the first period, the inventors demonstrated that the overall SOH Tot state of health of the battery had two components: a first component due to the SOH A state of health associated with phase A and a second due to the SOH B state of health associated with phase B.Furthermore, during this first period, they found that the variation in the overall SOH Tot health state was mainly due to the variation in the SOH B health state associated with phase B so that, as a first approximation, the overall SOH Tot health state could be deduced from the SHO A health state associated with phase A determined during a previous measurement, for example the health state (SOH A ) associated with the initial phase A (which can be given by the manufacturer or determined when the battery is installed), added to the SOH B health state associated with phase B. During the second period, the SOH B health state associated with phase B becomes zero and the overall SOH Tot health state then merges with the SOH A health state associated with phase A.In other words, knowing that the overall SOH Tot health state is presented as the sum of the SOH A health state associated with phase A and the SOH B health state associated with phase B, it therefore becomes possible, once such a decomposition has been demonstrated, to determine the overall SOH Tot health state of the battery based on at least one measurement of the SOH A health state associated with phase A and / or the SOH B health state associated with phase B, said measurement being for example carried out using a partial discharge on phase A and / or phase B.

[0030] In the following, several embodiments of this method will be presented in order to illustrate how it is possible to take advantage of the inventors' findings in order to determine the overall state of health SOH Tot of a battery from a charge or a partial discharge occurring in phase A or in phase B. By "a charge (respectively a discharge) occurring during phase Y" is meant the fact that during said charge (respectively said discharge), the state of charge SOC of the battery passes through all the values located between the two terminals of the phase considered. For example, if a charge occurs during phase A, then the state of charge during said charge will, at a minimum, vary from the transition state of charge (as defined above) to the maximum state of charge.Of course, the starting state of charge of said charge may be lower than the transition state of charge but, for the charge to be considered as being carried out during phase A, it cannot be higher than the latter.

[0031] In one embodiment, the SOH Y health state associated with phase Y with Y = A or B is measured using the following equation: SOH Y = 100 × Q Dch _ Y k Q Dch _ Tot 0 where SOH Y is the state of health associated with phase Y, Q Dch- Y(k) is the amount of cumulative Ah or cumulative Wh during a charge (respectively discharge) during phase Y at cycle k of charge (respectively discharge) and Q Dch- Tot(0) is the amount of cumulative Ah or cumulative Wh during a total charge (respectively discharge) in the first cycle. In other words, by measuring the cumulative quantity of Ah or Wh during a charge at a cycle k, for example a charge during phase A, and knowing the cumulative quantity of Ah or Wh during a total charge in the first cycle, it is possible to determine the state of health SOH A associated with phase A. The same is of course true for the state of health SOH B associated with phase B. The quantity of cumulative Ah or Wh during a total charge in the first cycle can for example be provided by the manufacturer in the same way as the other technical characteristics of the battery.Alternatively or additionally, this measurement can be carried out when a battery is installed in a device, for example in an electric vehicle.

[0032] As explained previously, thanks to the method according to the invention, it is possible to determine the overall state of health SOH Tot of a battery from a partial charge (respectively partial discharge) provided that said charge (respectively said discharge) is carried out during phase A or phase B. Depending on the phase during which the charge (respectively the discharge) is carried out, the steps to be carried out in order to determine the overall state of health SOH Tot of the battery may differ.

[0033] In one embodiment illustrated in Figure 4, when the partial charge (respectively, the discharge) occurs in phase A, the method 10 according to the invention comprises a step 1041A of measuring the state of health SOH A associated with phase A. As detailed previously, this measurement can be carried out by measuring the quantity of Ah accumulated during the charge (respectively the discharge) at a cycle k considered. The method also comprises, if the SOH B health state associated with phase B is zero, a step 1042A0 of determining the overall SOH Tot health state of the battery, said overall SOH Tot health state being equal to the SOH A health state associated with phase A determined in step 1041A of measuring the SOH A health state associated with phase A. Indeed, as detailed previously, when the SOH B health state associated with phase B becomes zero, the overall SOH Tot health state then merges with the SOH A health state associated with phase A.In the same way, when the state of health SOH B associated with phase B is non-zero, the method comprises a step 1042A1 of determining the overall state of health SOH Tot of the battery, said overall state of health SOH Tot being equal to the state of health SOH A associated with phase A determined in step 1041A of measuring the state of health SOH A associated with phase A added to the state of health SOH B associated with phase B determined during a previous measurement. Indeed, the value of the state of health SOH B associated with phase B may be known from a previous measurement. The previous measurement may for example be carried out during a residual discharge (i.e. a discharge aimed at emptying the battery completely from a low state of charge), such a measurement having the advantage of being able to be carried out quickly.Furthermore, when the value of the health state SOH B associated with phase B is measured as being equal to zero during a previous measurement, a boolean can be toggled to a "true" value so that for subsequent executions of the method 10 according to the invention, this information can be taken into account.

[0034] In one embodiment illustrated in Figure 4, when the partial charge (respectively discharge) occurs in phase B, the method 10 according to the invention comprises a step 1041B of measuring the state of health SOH B associated with phase B. As detailed previously, this measurement can be carried out by measuring the quantity of Ah accumulated during the charge (respectively the discharge) at a cycle k considered. The method 10 also comprises, if the state of health SOH A associated with phase A is known, a step 1042B1 of determining the overall state of health SOH Tot of the battery, said overall state of health SOH Tot being equal to the state of health SOH A associated with phase A added to the state of health SOH B associated with phase B determined in step 1041B of measuring the state of health SOH B associated with phase B. The value of the state of health SOH A associated with phase A can be known from a previous measurement.In the same way, the method 10 comprises, when the state of health SOH A associated with phase A is not known, a step 11042B0 of determining the overall state of health SOH Tot of the battery, said overall state of health SOH Tot being equal to the state of health SOH B associated with phase B determined in step 1041B of measuring the state of health SOH B associated with phase B added to the initial state of health SOH A associated with phase A (i.e. the state of health SOH A associated with phase A at the time of installation of said battery, the latter being able for example to be communicated by the manufacturer or measured during installation of the battery). In other words, the overall state of health SOH Tot can be calculated using the following formula: . SOH Tot t = SOH A t 0 + SOH B t

[0035] In one embodiment, the health state SOH Y associated with phase Y may be modeled by the following equation: SOH Y = max A Y x + B Y , 0 where AY and BY are constants and x is a number of equivalent cycles. In other words, the overall health status SOH Tot can be expressed using the following formula: SOH Tot = SOH A + SOH B = max A A x + B A , 0 + max A B x + B B , 0 The overall health status SOH Total during the first period can therefore be formulated as follows: SOH Tot = A A + A B x + B A + B B

[0036] As described earlier, during the second period, the SOH B health state associated with phase B is zero. The overall SOH Tot health state during the second period can therefore be formulated as follows: SOH Tot = A A x + B A

[0037] In other words, when the parameters {AA, AB, BA, BB} have been determined, it is possible to determine the overall health status SOH Tot by knowing the number x of equivalent cycles.

[0038] In one embodiment illustrated in Figure 5, in order to determine these parameters, the method 10 comprises a first phase IP, called the initialization phase and comprising at least one step 1051 of four measurements of the global SOH Tot health state, each measurement being carried out on a complete charge (respectively a discharge); and a step 1052 of determining the parameters {AA, AB, BA, BB} of the models associated with the SOH A health state associated with phase A and the SOH B health state associated with phase B. Indeed, by carrying out at least four measurements for four different global SOH Tot health states, it is possible, for example using a least squares method, to determine the parameters {AA, AB, BA, BB} as illustrated in Figure 3. Preferably, during the initialization IP phase, each measurement of the global SOH Tot health state is carried out so that the variation of the global SOH Tot health state between said measurement and the previous measurement is greater than 2% of the measured value. This makes it possible to obtain greater precision in the determination of the parameters {AA, AB, BA, BB}.

[0039] The method 10 also comprises a second MP phase, called the measurement phase. This MP measurement phase comprises a step 1053 of determining the number of equivalent cycles using a partial charge (respectively discharge) in phase A or phase B.

[0040] When charging (respectively discharging) during the MP measurement phase occurs during phase A, the number x of equivalent cycles is determined using the following formula: x = SOH A − B A A A

[0041] Similarly, when the charge (respectively discharge) during the MP measurement phase occurs during phase B, the number x of equivalent cycles is determined using the following formula: x = SOH B − B B A B

[0042] Once the number of equivalent cycles has been determined, the measurement phase MP includes a step 1054 for determining the overall SOH Tot health status. This determination is carried out using the following formula (already presented previously): SOH Tot = SOH A + SOH B = max A A x d + B A , 0 + max A B x d + B B , 0 where xd is the number of equivalent cycles determined during step 1053 of determining the number of cycles.

[0043] In order to implement a method according to a first aspect of the invention, a second aspect of the invention relates to a device DI for determining the state of health SOH Tot of a battery BAT comprising a measuring means MM for measuring the current entering and leaving the battery BAT as well as a calculating means MC connected to said measuring means MM. In addition, the calculating means MC is configured to implement a method 10 according to a first aspect of the invention. The calculating means MC can take the form of a processor associated with a memory (for example a RAM memory), an FPGA or even an ASIC card. Communication between the calculating means MC and the measuring means MM can be carried out via a bus or even by means of a wired network (for example Ethernet ®< ) or wirelessly (for example, WiFi ®< or Bluetooth ®< ).The calculation means MC can thus trigger a measurement, said measurement being carried out by the measurement means MM, but also receive the data resulting from the measurement. Thus, the calculation means MC is configured to implement, using the measurement means MM, a method 10 for determining the state of health SOH Tot of a battery BAT according to a first aspect of the invention, the instructions necessary for this implementation being for example stored on a memory (for example a hard disk or a flash memory connected to the calculation means MC) and loaded by the calculation means MC for their execution.

Claims

1. A method (10) for determining the state of health (SOH) of a battery, referred to as overall state of health, wherein the voltage across the battery as a function of the state of charge can be split into a first phase, referred to as phase A, and a second phase, referred to as phase B, phase A and phase B being distinct and consecutive, phase A being associated with a first state of health (SOHA) and phase B being associated with a second state of health (SOHB), the overall state of health (SOHTot) being equal to the sum of the state of health (SOHA) associated with phase A and the state of health (SOHB) associated with phase B, wherein the evolution of the overall state of health (SOHTot) can be divided into two consecutive periods, a first period during which the variation in the overall state of health (SOHTot) is mainly due to the variation in the state of health (SOHB) associated with phase B and a second period during which the state of health (SOHB) associated with phase B becomes zero and the overall state of health (SOHTot) is then the same as the state of health (SOHA) associated with phase A; the method being characterised in that it comprises: - when the charge, respectively discharge, occurs in phase A: ▪ a step (1041A) of measuring the state of health (SOHA) associated with phase A; ▪ if the state of health (SOHs) associated with phase B is zero, a step (1042A0) of determining the overall state of health (SOHTot) of the battery, said overall state of health (SOHTot) being equal to the state of health (SOHA) associated with phase A determined in the step (1041A) of measuring the state of health (SOHA) associated with phase A. ▪ if the state of health (SOHs) associated with phase B is non-zero, a step (1042A1) of determining the overall state of health (SOHTot) of the battery, said overall state of health (SOHTot) being equal to the state of health (SOHA) associated with phase A determined during the step (1041A) of measuring the state of health (SOHA) associated with phase A added to the state of health (SOHB) associated with phase B determined during a previous measurement; - and / or when the charge, respectively discharge, occurs in phase B: ▪ a step (1041B) of measuring the state of health (SOHB) associated with phase B; ▪ if the state of health (SOHA) associated with phase A is known, a step (1042B1) of determining the overall state of health (SOHTot) of the battery, said overall state of health (SOHTot) being equal to the state of health (SOHA) associated with phase A added to the state of health (SOHB) associated with phase B measured in the step (1041B) of measuring the state of health (SOHB) associated with phase B; ▪ if the state of health (SOHA) associated with phase A is not known, a step (1042B0) of determining the overall state of health (SOHTot) of the battery, said overall state of health (SOHTot) being equal to the state of health (SOHB) associated with phase B measured in the step (1041B) of measuring the state of health (SOHs) associated with phase B added to the state of health (SOHA) associated with the initial phase A.

2. The determining method according to the preceding claim, characterised in that the state of health (SOHY) associated with phase Y with Y = A or B is measured using the following equation: SOH Y = 100 × Q Dch _ Y k Q Dch _ Tot 0 where SOHY is the state of health associated with phase Y, QDch_Y(k) is the amount of Ah or Wh accumulated during a charge, respectively discharge, during phase Y at cycle k and QDeh_Tot(0) is the amount of Ah or Wh accumulated during a total charge, respectively discharge, at the first cycle.

3. The method (10) for determining the state of health (SOH) of a battery, referred to as overall state of health, the voltage across the battery as a function of the state of charge can be split into a first phase, referred to as phase A, and a second phase, referred to as phase B, phase A and phase B being distinct and consecutive, phase A being associated with a first state of health (SOHA) and phase B being associated with a second state of health (SOHB), the overall state of health (SOHTot) being equal to the sum of the state of health (SOHA) associated with phase A and the state of health (SOHB) associated with phase B, wherein the evolution of the overall state of health (SOHTot) can be divided into two consecutive periods, a first period during which the variation in the overall state of health (SOHTot) is mainly due to the variation in the state of health (SOHB) associated with phase B and a second period during which the state of health (SOHB) associated with phase B becomes zero and the overall state of health (SOHTot) is then the same as the state of health (SOHA) associated with phase A, method wherein the state of health (SOHY) associated with phase Y with Y = A or B can be modelled by the following equation: SOH Y = max A Y x + B Y , 0 where AX and BX are constants and x is a number of equivalent cycles; the method being characterised in that it comprises - a first phase (IP), referred to as the initialisation phase and comprising: - a step (1051) of performing at least four measurements of the overall state of health (SOHTot), each measurement being performed on a full charge, respectively discharge; - a step (1052) of determining the parameters of the models associated with the state of health (SOHA, SOHs) associated with phase A and phase B; - a second phase (MP), referred to as the measurement phase and comprising: - a step (1053) of determining the number of equivalent cycles using a partial charge, respectively discharge, in phase A or phase B; - a step (1054) of determining the overall state of health (SOHTot); the overall state of health (SOHTot) being determined from the model obtained during the initialisation phase (IP) and the number of equivalent cycles obtained during the measurement phase (MP).

4. The determining method according to the preceding claim, characterised in that, during the initialisation phase (IP), each measurement of the overall state of health (SOHTot) is performed so that the variation in the overall state of health between said measurement and the previous measurement is greater than or equal to 2% of the value of said measurement.

5. The method according to one of the two preceding claims characterised in that, when the charge (respectively, discharge) during the step (1053) of determining the number of equivalent cycles occurs during phase Y with Y = A or B, the number of equivalent cycles is determined using the following formula: x = SOH Y − B Y A Y 6. A device (DI) for determining the state of health of a battery comprising a measurement means (MM) for measuring the current entering and leaving the battery as well as a calculator means (MC) connected to said measurement means (MM) and configured to implement a method (10) according to any of claims 1 to 5.

7. A computer program comprising instructions which cause the device (DI) according to claim 6 to perform the steps of the method (10) according to any of claims 1 to 5.

8. A computer-readable medium, on which the computer program according to claim 7 is recorded.