Accumulator for the reversible electrochemical storage of electrical charge by means of a plurality of galvanic cells, as well as methods for its operation and motor vehicle

Abstract

Motor vehicle battery (20, 54) for the reversible electrochemical storage of electrical charge by means of a plurality of galvanic cells (22, 24, 26), with a first, a second and a third battery terminal (28, 30, 32) and with a first and a second cell block (36, 38), wherein the cell blocks (36, 38) each comprise at least one of the galvanic cells (22, 24, 26) and are connected in series to the first and the second battery terminal (28, 32) in order to provide a first battery voltage (40) between the first and the second battery terminal (28, 32), and wherein an electrical connection (44) of the first cell block (36) with the second cell block (38) is connected to the third battery terminal (30) in order to provide a second battery voltage between the first and the third battery terminal (28, 30). (42) to provide,wherein the charge storage capacity of the first cell block (36) is greater than the charge storage capacity of the second cell block (38), wherein the vehicle battery (20, 54) has a housing (34) on which the battery terminals (28, 30, 32) are arranged and in which all galvanic cells (22, 24, 26) of the first and second cell blocks (36, 38) are arranged, wherein the first battery terminal (28) is connected to the first cell block (36) and the second and third battery terminals (30, 32) are connected to the respective cell blocks (36, 38) via a respective electrical switching element (46, 48).

Description

[0001] The present invention relates to an accumulator for the reversible electrochemical storage of electrical charge by means of a plurality of galvanic cells, with a first, a second and a third accumulator terminal and with a first and a second cell block, wherein the cell blocks each have at least one of the galvanic cells and are connected in series to the first and the second accumulator terminal in order to provide a first accumulator voltage between the first and the second accumulator terminal, and wherein an electrical connection of the first cell block to the second cell block is connected to the accumulator terminal in order to provide a second accumulator voltage between the first and the third accumulator terminal.Furthermore, the invention relates to a motor vehicle with an electrical system and also to a method for operating an electrical system of a motor vehicle with a rechargeable battery, in which a plurality of galvanic cells reversibly electrochemically store electrical charge, wherein a first rechargeable battery voltage is provided between a first and a second rechargeable battery terminal by means of a series connection of a first and a second cell block each having at least one of the galvanic cells, and a second rechargeable battery voltage is provided between the first and a third rechargeable battery terminal connected to an electrical connection of the first cell block to the second cell block.

[0002] Accumulators of this generic type are generally known. They serve to reversibly store electrical energy. Such accumulators are used, in particular, in motor vehicles to supply the vehicle's electrical system with electrical energy. Furthermore, such accumulators also serve to provide electrical energy in electrically powered motor vehicles such as electric vehicles, hybrid vehicles, and / or the like. A motor vehicle is, in particular, a motor vehicle, preferably a passenger car. Furthermore, such accumulators are also used in the field of uninterruptible power supplies, such as those used in signaling technology or safety devices, or the like. In the automotive sector, such accumulators are frequently used in the form of lead-acid accumulators or nickel-cadmium accumulators.In particular, in electrically powered vehicles, so-called high-voltage batteries are used as accumulators. These batteries provide a direct current voltage that exceeds 60V and can reach up to about 1,500V, preferably 800V.

[0003] Typically, a rechargeable battery comprises a plurality of galvanic cells that can be electrically connected in series, in parallel, or in combinations thereof, particularly in a matrix circuit. Galvanic cells are often connected in parallel within a rechargeable battery. However, series connections of galvanic cells are also widespread, for example, in a well-known type of lead-acid rechargeable battery used in motor vehicles. In this case, the lead-acid rechargeable battery typically provides a 12V electrical system, for which purpose six galvanic cells are connected in series within the rechargeable battery. To enable a series connection of galvanic cells within the rechargeable battery, the galvanic cells are arranged opposite one another in an electrochemically insulated manner. This means that the electrolyte of one galvanic cell is not in contact with the electrolyte of another galvanic cell.

[0004] Galvanic cells are assembled in a predetermined number to form a battery and mechanically connected to each other. To achieve the desired interconnection, an electrical connection between the galvanic cells is also provided within the battery. This connection can also provide terminal connections for the battery or battery terminals, to which, for example, the vehicle's electrical system can be connected to ensure proper operation.

[0005] A galvanic cell comprises at least two electrodes, but usually exactly two electrodes, which are in electrochemical contact with each other, preferably via an electrolyte. Due to the electrochemical processes, an electrical voltage develops at the electrodes, which can be used to supply energy. The galvanic cell is designed to be able to absorb electrical energy and store it electrochemically, as well as to release electrical energy and thereby carry out an electrochemical process.

[0006] Particularly in motor vehicles, it is common today for two on-board electrical systems with different DC voltages to be provided due to the large number of electrical devices included in the vehicle's electrical system, for example, a first on-board electrical system with a DC voltage of approximately 12V and a second on-board electrical system with a DC voltage of approximately 48V. To implement these on-board electrical systems, two separate accumulators are generally provided, with one of the two accumulators being assigned to each of the two on-board electrical systems.

[0007] The two on-board electrical systems are electrically coupled via a switched-mode energy converter, namely a DC / DC converter. The accumulator for the 48V on-board electrical system is often a lithium battery, whereas the accumulator for the 12V on-board electrical system is usually a lead-acid battery. Both batteries are very large and heavy. The 12V accumulator must provide the vehicle's quiescent current while also being able to absorb dynamic load peaks and usually also provide cold starting. The 48V battery is typically designed to absorb recuperation current and, if necessary, supply boost current. Both batteries together are significantly larger and heavier than a 12V battery in a vehicle with a solely 12V on-board electrical system.Such an arrangement of the generic type is disclosed, for example, in DE 101 00 888 A1, which discloses a control unit for an on-board electrical system.

[0008] Furthermore, DE 103 04 764 B3 discloses an electrical system with a first 14V electrical system and a second 28V electrical system. The system comprises two 14V rechargeable batteries that are switchable, so that the batteries can be operated both in parallel and in series. Furthermore, DE 10 2012 017 674 A1 discloses a motor vehicle with a multi-voltage electrical system, in which a plurality of rechargeable batteries is provided to provide the electrical systems. Furthermore, DE 101 44 017 A1 discloses a system for balancing a battery module via a variable DC / DC converter in a hybrid electric drive train. A series connection of several rechargeable batteries is provided here. Finally, DE 10 2012 206 772 A1 discloses a backup storage unit with a center tap, which is provided in addition to an existing lead-acid rechargeable battery.Overall, however, it proves to be disadvantageous that a number of different accumulators are required to provide more than one on-board network.

[0009] Furthermore, DE 10 2005 038 746 A1 discloses a power supply in a motor vehicle. US 2015 / 0188331 A1 discloses a battery stack configuration in a multi-battery supply system. Furthermore, DE 299 19 099 U1 discloses a device for jump-starting motor vehicles with high on-board power supply voltages, e.g., 42 / 14 V on-board power supply, using a symmetrical, clocked DC / DC converter. Finally, DE 10 2014 201 358 A1 discloses an on-board power supply and a method for operating an on-board power supply.

[0010] It is therefore the object of the invention to achieve an improvement here and to reduce the effort required to provide more than one on-board network.

[0011] As a solution, the invention proposes an accumulator, a motor vehicle and a method according to the independent claims.

[0012] Further advantageous embodiments result from features of the dependent claims.

[0013] On the accumulator side, the invention proposes in particular that a charge storage capacity of the first cell block is greater than a charge storage capacity of the second cell block.

[0014] On the motor vehicle side, it is particularly proposed with regard to a generic motor vehicle that the electrical system in the motor vehicle comprises an accumulator of the invention.

[0015] With regard to a generic method, it is particularly proposed that a greater charge storage capacity is provided by the first cell block than by the second cell block.

[0016] The invention utilizes the knowledge that two on-board electrical systems with different direct voltages can be provided using just a single accumulator, namely by forming cell blocks. The invention utilizes the knowledge that the creation of two on-board electrical systems is made possible by allowing one of the cell blocks, preferably the first cell block, to be used jointly by both on-board electrical systems. This enables a high level of integration. For this purpose, however, it is necessary that the charge storage capacity of the two cell blocks is selected accordingly. Because the first cell block can be used by both on-board electrical systems, its charge storage capacity must be selected to be correspondingly higher than that of the second cell block.The invention makes it possible to provide, for example, a 12V electrical system in a motor vehicle, which provides the same level of functionality as can be achieved using a 12V rechargeable battery. At the same time, a 48V electrical system can be provided, which also provides the usual range of power. The charge storage capacity of the rechargeable battery's cell blocks can be selected according to the required power or energy quantities. This makes it possible to use only a single rechargeable battery to provide the desired electrical system. This significantly reduces the effort, particularly with regard to installation and maintenance.Furthermore, by providing only a single battery, an additional combinatorial effect can be achieved, namely because the first cell block can be used to power both on-board electrical systems. For example, the charge storage capacity of the first cell block can be 20 Ah and that of the second cell block 10 Ah.

[0017] The invention results in a further functional advantage in that the internal resistance in relation to the on-board electrical systems, in particular the second on-board electrical system, is lower than if a separate battery were used for each of the on-board electrical systems. This results from the fact that the first cell block as a whole has a significantly lower internal resistance due to its significantly higher capacity. The series connection results in particular in a reduction in the internal resistance in relation to the second on-board electrical system. Likewise, the increased charge storage capacity of the first cell block also results in a lower internal resistance compared to a separate accumulator for the first on-board electrical system. In this respect, a significant functional improvement can be achieved compared to the prior art.

[0018] It is proposed that the accumulator have a housing on which the accumulator terminals are arranged and in which all galvanic cells of the first and second cell blocks are arranged. This makes it possible to provide an easy-to-handle structural unit that allows the accumulator to be easily installed in the motor vehicle. Furthermore, the connection effort can be reduced because, in the accumulator of the invention, only three terminals need to be connected. In the prior art, by contrast, at least two terminals need to be connected for each of the accumulators. This not only provides assembly advantages but also allows for material savings.

[0019] The invention proposes that the first accumulator terminal be connected to the first cell block, and the second and third accumulator terminals be connected to the respective cell block via a respective electrical switching element. This makes it possible to protect the accumulator, in particular its galvanic cells, from overload as needed. The electrical switching element can, for example, be an electromechanical switching element in the form of a contactor or the like. Furthermore, the electrical switching element can also be formed by a semiconductor switch, for example a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), a GTO (Gate Turn-Off Thyristor), or the like. This arrangement also allows the first and / or second cell block to be deactivated as needed.This design takes into account that the first cell block can be used by both on-board electrical systems. Therefore, if, for example, protection of the first cell block is required, both switching elements are preferably activated. However, if only the second cell block is affected, the first cell block can continue to operate independently by adjusting the electrical switching elements accordingly. The electrical switching elements are preferably integrated into the battery housing. They can be connected to a higher-level vehicle control system.

[0020] It is particularly advantageous if at least one of the galvanic cells is a lithium-ion-based galvanic cell, in particular a lithium titanate-based galvanic cell. Using such galvanic cells can increase the overall performance of the accumulator or further reduce its size. Lithium titanate-based galvanic cells are particularly suitable for use in motor vehicles because, due to their physical and chemical properties, the uncontrolled release of energy is reduced in the event of damage to the galvanic cell. Thus, such galvanic cells offer an additional level of safety, particularly in motor vehicle operation. Further advantages arise from the reduced aging of such galvanic cells.Overall, the use of such galvanic cells leads to increased safety, especially in motor vehicles, especially in the event of an accident or similar.

[0021] A further embodiment of the invention provides that at least the first cell block comprises a plurality of galvanic cells connected in series. Preferably, the second cell block also comprises a plurality of galvanic cells connected in series. The number of galvanic cells to be connected in series is preferably selected according to the desired electrical first and second battery voltages.

[0022] Furthermore, it proves advantageous if galvanic cells are also connected in parallel, at least in the first cell block. This makes it easy to provide a correspondingly high charge storage capacity. This design is particularly advantageous because galvanic cells can be standardized and, as components, assembled in a modular fashion to form a battery in almost any way. This allows for further simplification and flexibility in battery production. Batteries can be manufactured almost individually and on demand at short notice from prefabricated galvanic cells, which are particularly standardized.

[0023] Furthermore, it proves advantageous if each of the two cell blocks has its own cell block management unit for monitoring and / or controlling a respective charge state. The cell block management units are preferably arranged integrated in the housing of the accumulator. By means of the cell block management units, a charge state of the respective cell block can be set or regulated. Furthermore, it can of course be provided that the respective cell block management unit also monitors further state variables of the respective assigned cell block, for example cell block voltage, voltage of the respective galvanic cells of the cell block, a temperature of the cell block and / or the respective galvanic cells of the cell block, an electrolyte composition of the galvanic cells belonging to the cell block and / or the like.In addition, the cell block management unit can also be used to control the electrical switching element accordingly. For this purpose, the cell block management units can also be provided to communicate with each other, thus enabling joint control of the electrical switching elements. In this way, the switching of the electrical switching elements can be realized depending on the state variables of both cell blocks. Alternatively or additionally, the cell block management units can also be connected to a higher-level vehicle control system.

[0024] In terms of the method, it is further proposed, in particular, that outside of the intended driving operation of the motor vehicle, the charge state of the first cell block be set higher than the charge state of the second cell block. This also allows the internal resistance of the first cell block to be further reduced, because the internal resistance can also depend, among other things, on the charge state of the respective cell block. This allows the operation of the respective on-board electrical system, in particular the on-board electrical system provided solely by the first cell block, to be improved at low temperatures.

[0025] The advantages and features described above apply equally to the motor vehicle according to the invention and to the method according to the invention.

[0026] Further advantages and features can be found in the following description of exemplary embodiments. In the figures, identical reference numerals denote identical features and functions.

[0027] They show: Fig. 1 shows a schematic circuit diagram of an electrical system of a motor vehicle (not shown in more detail) with two on-board networks and one accumulator for each of the two on-board networks, Fig. 2 is a schematic circuit diagram of an electrical system of a motor vehicle (not shown in detail) with two on-board networks and with an accumulator according to the invention according to a first embodiment, Fig. 3 a schematic sectional view through the accumulator based on Fig. 2, Fig. 4 a perspective view of an accumulator arranged in a housing according to Fig. 3, Fig. 5 a table with operating values ​​of the accumulator according to Fig. 4, and Fig. 6 a schematic circuit diagram of a further embodiment with an electrical system of a motor vehicle not shown in detail, which has a further embodiment of an accumulator according to the invention.

[0028] Fig. 1 shows a schematic circuit diagram of a section of an electrical system of a motor vehicle (not shown in detail) according to the prior art. The electrical system comprises a first electrical system 70, which is designed for an operating DC voltage of 12 V. In addition, the electrical system 72, which is designed for an operating DC voltage of 48 V. The first electrical system 70 has an accumulator 62, which in this case is embodied as a lead-acid accumulator. Furthermore, a switchable consumer 64 and a starter 66 for an internal combustion engine of the motor vehicle are connected to the first electrical system 70. A second accumulator 60, which in this case is embodied as a lithium-ion battery, is connected to the second electrical system 72. In addition, a switchable consumer 58 and an electric machine 68 are connected to the second electrical system 72.The electric machine 68 is part of a drive unit of the motor vehicle (not shown in detail). This enables the motor vehicle to be driven electrically. With the electric machine, electrical energy can be generated during normal driving and supplied to the accumulator 60. Conversely, electrical energy can also be provided from the accumulator 60 to support the driving operation of the motor vehicle by means of the electric machine 68. The consumers 58, 64 represent electrical devices that are supplied with electrical energy from the respective on-board electrical systems 70, 72. Furthermore, the first on-board electrical system 70 is electrically coupled to the second on-board electrical system 72 via a DC / DC converter 56. This makes it possible to exchange electrical energy between the on-board electrical systems 70, 72. The electrical coupling is thus bidirectional.Even if this design of the electrical system has proven to be effective, it still proves to be disadvantageous that two separate accumulators 60, 62 have to be provided.

[0029] Fig. Figure 2 now shows an embodiment according to the invention, based on the electrical system according to Fig. 1, whereby now the two accumulators 60, 62 of the design according to the prior art, as described in Fig. 1, is replaced by a single accumulator 54 according to the invention. The electrical system comprises, in addition to the accumulator 54, the units previously used for Fig. 1, which is why this description is used for Fig. 1 is referred to.

[0030] In contrast to Fig. 1 is for the electrical system according to Fig. 2, only a single accumulator, namely the accumulator 54, is now provided. In the present case, this has two cell blocks 36, 38, each comprising galvanic cells 22. The galvanic cells 22 are designed as lithium titanate-based galvanic cells and are provided as standardized components. Thirteen galvanic cells are connected in series in the cell block 38. Twelve galvanic cells 22 are provided in the cell block 36, six of which are each connected in series. The two series circuits formed thereby are again connected in parallel within the cell block 36. Both cell blocks 34, 36 therefore use the same type of galvanic cells 22. The two cell blocks 36, 38 are electrically coupled to one another at an electrical connection point 44. As a result, the two cell blocks 38, 36 are connected in series.

[0031] The series-connected cell blocks 36, 38 are connected to the battery terminals 28, 32. This provides a first battery voltage 40 of approximately 48V. The electrical connection 44, on the other hand, is connected to the third battery terminal 30. This provides a second battery voltage 42, which in this case is approximately 12V, between the first battery terminal 28 and the third battery terminal 30. As a result, the battery 54 provides the battery voltages 12V and 48V with a single unit, in contrast to the prior art, as described in Fig. 1 is ready.

[0032] In the present case, each of the galvanic cells 22 is provided with a charge storage capacity of approximately 10 Ah. This results in the second cell block 38 also having a charge storage capacity of 10 Ah. Since the first cell block 36 is connected in parallel, it has a charge storage capacity of approximately 20 Ah. As a result, the charge storage capacity of the first cell block 36 is greater than the charge storage capacity of the second cell block 38.

[0033] The accumulator 54 further comprises a housing 34 ( Fig. 3, Fig. 4) on which three accumulator terminals 28, 30, 32 are arranged in order to be able to electrically connect the accumulator 54 to the electrical system.

[0034] All galvanic cells 22 of the two cell blocks 36, 38 are arranged in the housing 34. Fig. 3 shows a corresponding section through an accumulator 54, as it is used in the embodiment according to Fig. 2 is used. From Fig. 2 further shows that the second accumulator terminal 32 is connected to the second cell block 38 via an electromechanical switching element 48, in this case a relay. Likewise, the third accumulator terminal 30 is connected to the electrical connection 44 via another electrical switching element 46, in this case a monostable relay.

[0035] Out of Fig. 3 shows that the galvanic cells 22 in the first cell block are connected in parallel pairs and then in series, specifically by means of electrical connecting elements 76. In the second cell block 38, however, the galvanic cells 22 are simply connected in series by means of electrical connecting elements 74. As a result, a higher charge storage capacity can be provided in the first cell block 36 than in the second cell block 38. This allows the galvanic cells 22 to be standardized and the accumulator 54 to be manufactured almost individually by assembling a corresponding number and corresponding interconnection of the galvanic cells 22 in the housing 34. Fig. 4 shows an embodiment of the housing 34 for the accumulator according to Fig. 3. It can be seen that in addition to the accumulator connections 28, 30, 32, a vehicle connection plug 78 is additionally provided, by means of which the accumulator can be connected to a higher-level vehicle control system of the motor vehicle.

[0036] Fig. 5 now shows in a table some operating values ​​of the accumulator according to Fig. 4. The table shows that the invention reduces the internal resistance, which allows a very high load capacity to be achieved even at low temperatures.

[0037] Fig. Figure 6 shows a further embodiment of an accumulator 20 of the invention, arranged in an electrical system as already described in the Fig. 1 and Fig. 2, which is why reference is made to the relevant explanations. The electrical system according to Fig. 6 comprises instead of the accumulator 54 the Fig. 2 now the accumulator 20. Otherwise, the design of the electrical system corresponds to what was already explained above.

[0038] The accumulator 20 also has a housing 34 in which a first and a second cell block 36, 38 are electrically connected to one another at an electrical connection 44. The series circuit formed thereby is in turn connected to the first and second accumulator terminals 28, 32, wherein the electrical connection 44 is connected to the third accumulator terminal 30. Here, too, electrical switching elements 46, 48 are provided, as already described for Fig. 2 were explained.

[0039] In contrast to the design according to Fig. 2, this accumulator comprises a respective battery management system 50, 52 for each of the cell blocks 36, 38. The battery management systems 50, 52 detect the charge states of the respective galvanic cells 24, 26 of the cell blocks 36, 38 and control them. Furthermore, the battery management systems 50, 52 are connected to the higher-level vehicle control system via the vehicle connector 78. In contrast to the embodiment according to Fig. 2, it is provided that both the first cell block 36 and the second cell block 38 each comprise exclusively galvanic cells connected in series. For this purpose, the first cell block 36 comprises galvanic cells 24, in this case lithium titanate-based galvanic cells, wherein each of the galvanic cells 24 has a capacity of approximately 20 Ah. In addition, the second cell block 38 comprises galvanic cells 26, which are also designed as lithium titanate-based galvanic cells and which have a charge storage capacity of approximately 10 Ah. As a result, compared to the embodiment according to Fig. 2 the internal parallel connection of galvanic cells within the first cell block 36. In principle, however, approximately the same properties as with the accumulator 54 can be achieved with the accumulator 20.

[0040] In the present case, it is further provided that the battery management systems 50, 52 set the state of charge of the first cell block 36 to be higher than the state of charge of the second cell block 38 outside of normal driving operation of the motor vehicle. In the present case, it is provided that the state of charge (SOC) of the first cell block is set to approximately 70 percent. The state of charge of the second cell block 38 is set to a lower level, to approximately 50 percent or less, depending on the total charge available.

[0041] The advantages, features, and embodiments described for the invention apply to the accumulator according to the invention, as well as to the motor vehicle equipped with the accumulator according to the invention, and to the method according to the invention. Accordingly, corresponding method features can also be provided for device features, and vice versa. The exemplary embodiments serve merely to explain the invention and are not limiting.

Claims

[1] Motor vehicle accumulator (20, 54) for the reversible electrochemical storage of electrical charge by means of a plurality of galvanic cells (22, 24, 26), with a first, a second and a third accumulator terminal (28, 30, 32) and with a first and a second cell block (36, 38), wherein the cell blocks (36, 38) each have at least one of the galvanic cells (22, 24, 26) and are connected in series to the first and the second accumulator terminal (28, 32) in order to provide a first accumulator voltage (40) between the first and the second accumulator terminal (28, 32), and wherein an electrical connection (44) of the first cell block (36) with the second cell block (38) is connected to the third accumulator terminal (30) in order to provide a second to provide accumulator voltage (42),wherein a charge storage capacity of the first cell block (36) is greater than a charge storage capacity of the second cell block (38), wherein the motor vehicle accumulator (20, 54) has a housing (34) on which the accumulator terminals (28, 30, 32) are arranged and in which all galvanic cells (22, 24, 26) of the first and second cell blocks (36, 38) are arranged, wherein the first accumulator terminal (28) is connected to the first cell block (36) and the second and third accumulator terminals (30, 32) are connected to the respective cell block (36, 38) via a respective electrical switching element (46, 48). [2] Motor vehicle accumulator according to claim 1, characterized by that at least one of the galvanic cells (22, 24, 26) is a lithium-ion-based galvanic cell, in particular a lithium titanate-based galvanic cell. [3] Motor vehicle accumulator according to one of the preceding claims, characterized bythat at least the first cell block (36) has a plurality of galvanic cells (22, 24) connected in series. [4] Motor vehicle accumulator according to claim 3, characterized by that at least in the first cell block (36) galvanic cells (22) are also connected in parallel. [5] Motor vehicle accumulator according to one of claims 1 to 4, characterized by that each of the two cell blocks (36, 38) has its own cell block management unit (50, 52) for monitoring and / or controlling a respective charge state of the cell blocks (36, 38). [6] Motor vehicle with an electrical system, characterized by that the electrical system comprises a motor vehicle accumulator (20, 54) according to one of the preceding claims. [7] Method for operating an electrical system of a motor vehicle with a motor vehicle accumulator (20, 54), in which a plurality of galvanic cells (22, 24, 26) reversibly electrochemically store electrical charge, wherein a first accumulator voltage (40) is provided between a first and a second accumulator terminal (28, 32) by means of a series connection of a first and a second cell block (36, 38) each having at least one of the galvanic cells (22, 24, 26), and a second accumulator voltage (42) is provided between the first and a third accumulator terminal (28, 30) connected to an electrical connection (44) of the first cell block (36) to the second cell block (38), wherein a greater charge storage capacity is provided by the first cell block (36) than by the second cell block (38), wherein the accumulator terminals (28, 30,32) are arranged on a housing (34) and all galvanic cells (22, 24, 26) of the first and second cell blocks (36, 38) are arranged in the housing (34), wherein the first accumulator terminal (28) is connected to the first cell block (36) and the second and third accumulator terminals (30, 32) are connected to the respective cell block (36, 38) via a respective electrical switching element (46, 48). [8] Method according to claim 7, characterized by that outside of a normal driving operation of the motor vehicle, a charge state of the first cell block (36) is set higher than a charge state of the second cell block (38).

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