TW202025538A - Battery module and energy storage system containing the same - Google Patents

Abstract

A battery module includes a plurality of battery cells and at least one conductive sheet. The at least one conductive sheet is electrically connected to the battery cells, and the at least one conductive sheet comprises a surface and a plurality of protrusions. The protrusions are formed on the surface and protrude from the surface, and a plurality of through holes are formed on the surface for shortening a width of the current path of the at least one conductive sheet.

Description

Battery module and energy storage system containing it

The present invention relates to an energy storage system and an energy storage system containing it, and more particularly to a battery module that uses a conductive sheet to adjust impedance and an energy storage system containing it.

Figure 1 shows a perspective view of a conventional servo energy storage cabinet. As shown in FIG. 1, the conventional servo energy storage cabinet 100 includes a housing 110 and a plurality of battery modules 120. The battery modules 120 are disposed in the housing 110 and are electrically connected to each other. With the increasing demand for high power in the system, the battery modules 120 carried by the battery system of the servo energy storage cabinet 100 are also increasing, so the impedance uniformity design requirements of the battery modules 120 are becoming increasingly stringent. In order to overcome the aforementioned problems, traditionally, power components are added to adjust the overall impedance of the battery module 120.

FIG. 2 shows an exploded view of a battery module according to an embodiment of the invention. As shown in FIG. 2, the battery module 120 includes a plurality of cylindrical battery cells 121, at least one cell holder 123 and a plurality of conductive sheets 124. The brackets 123 define a plurality of battery accommodating spaces for placing and fixing the battery cells 121, and the battery cells 121 are respectively stacked in the longitudinal direction x and the width direction z of the brackets 123. The conductive sheets 124 are respectively arranged on two ends of the battery cell 121 to connect the battery cells 121 in parallel or in series to form a plurality of battery cell arrays. The conductive sheets 124 are welded to each battery cell 121 by welding to achieve Series and parallel functions. The battery module 120 further includes a circuit board 126. The circuit board 126 may be a BMS control board. The at least one bracket 123 further defines an accommodating space for accommodating the circuit board 126. The conductive sheets 124 of the final positive electrode or negative electrode located at both ends of the battery module 120 are fastened to the circuit board 126 by screws 125, and the circuit board 126 is also fastened to the bracket 123 by screws 125. The circuit board 126 is provided with a plurality of electrical connectors.

Figure 3 shows a top view of a conventional conductive sheet. As shown in FIG. 3, in order to be able to electrically weld the conductive sheets 124 to the battery cells 120 more smoothly, a slot 140 is formed on the conductive sheet 124 corresponding to the electrode of the battery cell 120. The slot 140 separates the two electric solder joints 142, so that the current can bypass the slot 140 and travel a longer distance, thereby increasing the temperature of the electric solder joint 142. Such a design can enhance the fixing effect of electric welding and prevent the conductive sheet 120 from moving or shaking.

Figure 4 shows a schematic circuit diagram of a conventional servo energy storage cabinet. As shown in FIG. 4, the battery modules 120 of the servo energy storage cabinet 100 are connected in parallel with each other. When the overall impedances of the battery modules 120 are not the same, the current will flow to the battery module 120 with a low impedance, and the single battery module 120 may be damaged due to excessive current. Traditionally, the battery module 120 also includes a power element 127 which can be installed on the circuit board 126 to adjust the overall impedance of the battery module 120 so that the overall impedance of the battery modules 120 of the servo energy storage cabinet 100 can be mutually connected. To match.

The traditional use of adding power elements 127 to adjust the overall impedance of the battery module 120, because it is a single point of local heating, that is, only the power element 127 heats up, so the required auxiliary heat dissipation components are very large. Often the temperature rise of the power element 127 is too high, causing safety problems. Therefore, how to adjust the overall impedance of the battery module 120, while taking into account the heat dissipation problem, and simplifying the manufacturing process and reducing the cost without adding the power element 127, are issues worthy of discussion at present.

The purpose of an embodiment according to the present invention is to provide a battery module whose conductive sheet improves the impedance value, while taking into account the heat dissipation problem, and can simplify the manufacturing process and reduce the cost. The purpose of another embodiment is to include the aforementioned battery module and the energy storage system of another battery module. The conductive sheets of the two different battery modules have different structures, so that the overall impedance of the two different battery modules is different. Match each other.

According to an embodiment of the present invention, a battery module includes a plurality of battery cells and at least one conductive sheet. At least one conductive sheet is electrically connected to the battery cores, and the conductive sheet includes a surface and a plurality of protrusions. The protrusions are formed on the surface and protrude from the surface, and a plurality of through holes are formed on the surface to shorten the width of the current path of the at least one conductive sheet.

In one embodiment, each of the protrusions includes a heat dissipation surface, and the heat dissipation surface includes a first side and a second side. An opening is defined on the first side boundary. The second side is connected to the surface.

In one embodiment, the heat dissipation surface further includes a third side connected to the surface. One ends of the second side and the third side are connected to the first side, and the other ends of the second side and the third side are connected to each other. The multiple cross-sections of the heat dissipation surface facing the first side are closer to the first The area of the cross section of the side is greater than the area of the cross section farther from the first side.

In an embodiment, the other end of the second side and the third side of the heat dissipation surface is connected to a point, and the opening faces a first direction, and the first direction is not parallel to the surface Normal direction. Preferably, the heat dissipation surface of each of the protrusions forms a semi-conical shape.

In one embodiment, among the cross sections of the heat dissipation surface facing the first side, the area of the cross section closer to the first side is smaller than the area of the cross section farther from the first side. Preferably, the opening faces a first direction, and the first direction is parallel to the normal direction of the surface.

In one embodiment, the heat dissipation surface includes a third side and a fourth side. The third side boundary defines another opening and is opposite to the first side. The fourth side is connected to the surface and opposite to the second side. Preferably, the opening faces a first direction. The other opening faces a second direction, and neither the first direction nor the second direction is parallel to the normal direction of the surface.

In one embodiment, each of the protrusions includes a heat dissipation surface, and the heat dissipation surface further includes: a first side and a second side. The first side faces away from the surface. The second side is connected to the surface. Two of the protrusions are provided on two opposite sides of the surface defining the through hole.

In one embodiment, at least one conductive sheet includes a plurality of electrode end portions and a plurality of connection channel portions. Each of the connecting channel portions is connected between two adjacent electrode end portions, and the protruding portion and the through holes are provided in each of the connecting channel portions.

According to an embodiment of the present invention, an energy storage system includes the battery module as described above; and another battery module. The other battery module includes: a plurality of other battery cells and at least another conductive sheet, which are arranged on both ends of the other battery cells for connecting the other battery cells in series or in parallel.

According to an embodiment of the present invention, the conductive sheet of the battery module is provided with a plurality of protrusions and a plurality of through holes. The through hole can shorten the width of the current path of the conductive sheet. The protrusion can provide heat dissipation function and reduce the temperature rise effect caused by the increase in impedance. Therefore, through the design of the conductive sheet, the overall impedance of the battery module in the power storage system and the other battery module can be matched with each other, without increasing the installation of power components and without adding additional costs.

100‧‧‧Servo Energy Storage Cabinet

110‧‧‧Shell

120‧‧‧Battery Module

121‧‧‧Battery cell

123‧‧‧bracket

124‧‧‧Conductive sheet

125‧‧‧Be screwed

126‧‧‧Circuit board

127‧‧‧Power Components

140‧‧‧Slotting

142‧‧‧soldering point

200‧‧‧Energy Storage System

210‧‧‧Module shell

220a‧‧‧Battery Module

220b‧‧‧Battery Module

221‧‧‧These battery cells

224a‧‧‧Conductive sheet

224b‧‧‧Another conductive sheet

228‧‧‧Module shell

241a‧‧‧Slotting

243‧‧‧soldering point

245‧‧‧electrode end

246‧‧‧Connecting channel part

Positioning hole of 311‧‧‧

411‧‧‧Protrusion

412‧‧‧Through hole

421‧‧‧surface

430‧‧‧Radiating surface

431‧‧‧First side

432‧‧‧Second side

433‧‧‧ third side

434‧‧‧fourth side

439‧‧‧Open

Figure 1 shows a perspective view of a conventional servo energy storage cabinet.

Figure 2 shows an exploded view of a conventional battery module.

Figure 3 shows a top view of a conventional conductive sheet.

Figure 4 shows a schematic circuit diagram of a conventional servo energy storage cabinet.

Fig. 5 shows a perspective view of an energy storage system according to an embodiment of the invention.

FIG. 6A shows a side view of a battery module according to an embodiment of the invention.

FIG. 6B shows a side view of another battery module according to an embodiment of the invention.

FIG. 7 shows a top view of a conductive sheet according to an embodiment of the invention.

FIG. 8A shows an enlarged view of a part of a conductive sheet according to an embodiment of the present invention.

FIG. 8B shows an enlarged view of a part of a conductive sheet according to another embodiment of the present invention.

FIG. 8C shows an enlarged view of a part of a conductive sheet according to another embodiment of the present invention.

FIG. 8D shows an enlarged view of a part of a conductive sheet according to another embodiment of the present invention.

Fig. 5 shows a perspective view of an energy storage system according to an embodiment of the invention. As shown in FIG. 5, according to an embodiment of the present invention, the energy storage system 200 includes a module housing 210, a battery module 220a, and another battery module 220b. In this embodiment, the energy storage system 200 may be a servo energy storage cabinet. The battery module 220a and the other battery module 220b are arranged in the module housing 210, and are electrically connected in parallel with each other.

FIG. 6A shows a side view of a battery module according to an embodiment of the invention. FIG. 6B shows a side view of a battery module according to an embodiment of the invention. As shown in FIG. 6A, the battery module 220a includes a module housing 228, a plurality of cylindrical battery cells 221, and a plurality of conductive sheets 224a. As shown in FIG. 6B, another battery module 220b includes a module housing 228, a plurality of cylindrical battery cells 221, and a plurality of other conductive sheets 224b. The module housing 228 is used for accommodating the battery cells 221. In one embodiment, the battery cells 221 may be supported by a bracket (not shown) and housed in the module housing 228. The conductive sheets 224a and the other conductive sheets 224b are respectively placed on both ends of the battery cells 221 to form a plurality of battery arrays in parallel with the battery cells 221, and to connect the battery arrays in series, and A battery module 220b and another battery module 220a are formed.

In one embodiment, a fixing groove is formed on the bracket, and the module housing 228 is supported by the bracket groove The type structure is fixed, the conductive sheets 224a and 224b used for spot welding during production can be placed on the bracket, and the bracket may have positioning pins passing through the positioning holes 311 of the conductive sheets 224a and 224b for positioning, and then the spot welding process is performed.

The structure of the battery module 220a is similar to the structure of the other battery module 220b. Therefore, the same components use the same symbols. The following describes at least one difference between the two. The battery module 220a includes a conductive sheet 224a, and the structure of the current path of the conductive sheet 224a is different from the structure of the current path of the other conductive sheet 224b. According to the aforementioned characteristics, the overall impedance value of the battery module can be adjusted, while the heat dissipation problem is considered, and the manufacturing process and cost can be simplified without adding power components. The differences between the two conductive sheets will be described in more detail below.

FIG. 7 shows a top view of a conductive sheet according to an embodiment of the invention. As shown in FIG. 7, the conductive sheet 224 a includes a plurality of electrode end portions 245 and a plurality of connection channel portions 246. The connecting channel part 246 is connected between two adjacent electrode end parts 245. The conductive sheet 224 a includes a surface 421, a plurality of protrusions 411 and a plurality of through holes 412. In this embodiment, the protrusions 411 are located in a connecting channel part 246. The protrusion 411 is formed on the surface 421 and protrudes from the surface 421. A plurality of through holes 412 are formed on the surface 421. The through holes 412 penetrate the entire conductive sheet 224a to shorten the width of the current path of the conductive sheet 224a. As shown in FIG. 6B, the other conductive sheet 224b does not include the protrusions 411 and the through holes 412. Therefore, the width of the current path of the other conductive sheet 224b is different from the width of the current path of the conductive sheet 224a.

Each electrode end 245 includes a slot 241 a and two electric welding points 243. Slot 241a and conductive The edge of the surface of the sheet 224a forms at least one current path, and the slot 241a is located between the two electric welding points 243 and separates the two electric welding points 243, so that the electric welding current can bypass the slot 241a. In this embodiment, The slot 241a is elongated, and in one embodiment is an I-shape.

The overall impedance of the battery module includes the impedance of the printed circuit board assembly (PCBA), the impedance of the battery cell, the impedance of the conductive sheet, the impedance of the cable, and the impedance of the terminal device. Since the energy storage system 200 requires a lot of battery cells 221, the battery cells 221 may have different impedances due to different manufacturing processes of different suppliers. In order to make each battery module of the energy storage system 200 have the same impedance, In the prior art, power components, such as mercury components, semiconductors, etc., are added to the printed circuit board assembly. But this will have additional costs such as high cost, additional circuits, heat generation, etc. Moreover, when the heat generation is high, an additional heat dissipation module is required. In addition to increasing the cost, additional space for the heat dissipation module is also required.

On the contrary, according to the present invention, by forming a plurality of protrusions 411 and a plurality of through holes 412 on the conductive sheet 224a, the through holes 412 can change the width of the current path of the conductive sheet 224a to adjust the impedance value of the conductive sheet 224a. , And further achieve the uniform impedance design of the battery modules 220a and 220b. The protrusions 411 can not reduce the heat dissipation area, even increase the heat dissipation area, and provide an air flow channel for heat dissipation to increase the heat dissipation efficiency.

For example, when the impedance of the battery cells 221 of another battery module 220b is 60mΩ; the impedance of the other conductive sheets 224b is 40mΩ; and the impedance of the battery cells 221 of the battery module 220a is 40mΩ , Only need to provide multiple protrusions 411 and multiple through-holes on the conductive sheet 224a The hole 412 can increase the impedance of the conductive sheets 224a to 60mΩ, so that the overall impedance of the other battery module 220b and the battery module 220a are both 100mΩ. With this design, no additional components can be added, and the manufacturing cost can be reduced. In addition, since the overall impedance of the other battery module 220b and the battery module 220a are both 100mΩ, when a short circuit occurs outside the energy storage system 200, the current will not be fully fed back to the battery cells 221 with an impedance of 40mΩ. As a result, the battery module 220a bears all the current and is damaged due to exceeding the capacity.

In addition, since the conductive sheets 224a of the battery module 220a and the other conductive sheets 224b of the other battery module 220b are evenly arranged on the two ends of the battery cells 221, the heat generation is relatively uniform and there is no localization. Excessive local temperature caused by heating. In addition, the conductive sheets 224a all directly contact the battery cells 221, so when the conductive sheets 224a generate heat, they can also dissipate heat to the battery cells 221 without concentrating the heat locally.

As described above, according to an embodiment of the present invention, the through holes 412 are used to change the length and width of the current travel path to adjust the impedance value of the conductive sheet, and the increased impedance is distributed to the conductive sheets. In addition, the use of these protrusions 411 without reducing the heat dissipation area can even increase the heat dissipation area and provide an air flow channel for heat dissipation, which facilitates heat dissipation and cools the overall battery module. The present invention is not limited, and the shape, structure, number, etc. of the protrusions 411 and the through holes 412 can be appropriately designed according to the generated differences. The present invention is also not limited. The method of manufacturing the protrusions 411 and the through holes 412, in one embodiment, can be manufactured by stamping, and the original through hole 412 is used as the material of the protrusion 411, so No additional materials can be used.

FIG. 8A shows an enlarged view of a part of a conductive sheet according to an embodiment of the present invention. As shown in FIG. 8A, the protrusion 411 includes a heat dissipation surface 430. The heat dissipation surface 430 includes: a first side 431 defining an opening 439; and a second side 432 connected to the surface 421. In this embodiment, the heat dissipation surface 430 further includes a third side 433 connected to the surface 421. One ends of the second side 432 and the third side 433 are connected to the first side 431, and the other ends of the second side 432 and the third side 433 are connected to each other, and the heat dissipation surface 430 faces the first side 431 The area of the cross section closer to the first side 431 is larger than the area of the cross section farther from the first side 431.

The opening 439 is connected to the through hole 412, and the first side 431, the second side 432, and the third side 433 extend upward from the surface 421 at the wall defining the surface 421 of the through hole 412. In this embodiment, the other ends of the second side 432 and the third side 433 of the heat dissipation surface 430 are connected to a point, and the opening 439 faces a first direction, and the first direction is not parallel to the normal line of the surface 421 The direction, preferably the first direction is substantially perpendicular to the normal direction of the surface 421. More specifically, the heat dissipation surface 430 of the protrusion 411 is formed in a semi-conical shape, which can increase the area of the heat dissipation surface 430. In addition, since the opening 439 is connected to the through hole 412, air can flow in from the opening 439 and flow out from the through hole 412, or vice versa, so that the air flow can be smoother and the heat dissipation effect can be increased.

As shown in FIG. 8A, the protrusion 411 is a half-broken convex hull formed by a stamping process. When current flows through this section, the through hole 412 of the convex hull is broken and blocked, and the cross-sectional width through which the current can flow is relatively reduced. , The effect is equivalent to reducing the width of the conductive sheet, thereby increasing the resistance value, and because the convex hull is half broken instead of a hole, the original is retained and the cross-sectional area of the nickel sheet (as the heat dissipation surface 430) is increased for heat dissipation, so the narrowing can be reduced The width of the conductive sheet (nickel sheet) causes the problem of excessive temperature rise of the conductive sheet (nickel sheet). Yu Yi In an embodiment, the thickness of the first side 431 of the heat dissipation surface 430 is smaller than the thickness of the conductive sheet 224a, so the total area of the heat dissipation surface 430 is greater than the area of the through hole 412. More specifically, when the conductive sheet 224a is punched, in addition to forming the through hole 412, the material originally located in the through hole 412 is retained to form the heat dissipation surface 430, and the thickness of the first side 431 is smaller than that of the conductive sheet 224a. To increase the heat dissipation area of the heat dissipation surface 430.

In one embodiment, the number and size of the half-broken convex hulls can be adjusted according to the current density distribution and impedance value requirements, so that the system can be optimally designed between the temperature rise and heat dissipation and the impedance value increase requirements, such as low current density Place more or larger half-broken convex hulls at high current density to increase the impedance value, and place fewer or smaller half-broken convex hulls at high current density to increase the impedance value while retaining and increasing the original cross-sectional area of the nickel sheet In order to dissipate heat, the impedance value can be increased at the same time but the problem of excessive temperature rise of the nickel sheet caused by the narrowing of the width of the nickel sheet can be avoided. Therefore, compared with the prior art, an embodiment of the present invention has the effect of increasing the impedance value, solving the heat dissipation problem, simplifying the manufacturing process and reducing the cost.

FIG. 8B shows an enlarged view of a part of a conductive sheet according to another embodiment of the present invention. As shown in FIG. 8B, the heat dissipation surface 430 of the protrusion 411 includes: a first side 431 defines an opening 439; and a second side 432 is connected to the surface 421. Among the multiple cross sections of the heat dissipation surface 430 facing the first side 431, the area of the cross section closer to the first side 431 is smaller than the area of the cross section farther from the first side 431. The opening 439 faces a first direction and the first direction is parallel to the normal direction of the surface 421. The opening 439 communicates with the through hole 412. Moreover, the second side 432 extends upward from the surface 421 at the wall defining the surface 421 of the through hole 412.

FIG. 8C shows an enlarged view of a part of a conductive sheet according to another embodiment of the present invention. As shown in FIG. 8C, the heat dissipation surface 430 of the protrusion 411 includes: a first side 431 defines an opening 439; a second side 432 is connected to the surface 421; a third side 433 defines another opening 439 , And opposite to the first side 431; and a fourth side 434, connected to the surface 421, and opposite to the second side 432. The opening 439 defined by the first side 431 faces a first direction, the other opening 439 defined by the third side 433 faces a second direction, and the second direction is opposite to the first direction, and the first direction and the first direction Neither direction is parallel to the normal direction of the surface 421. In an embodiment, the second direction may not be opposite to the first direction. The opening 439 and the other opening 439 are both connected to the through hole 412 and serve as an air flow channel.

FIG. 8D shows an enlarged view of a part of a conductive sheet according to another embodiment of the present invention. As shown in FIG. 8D, the protrusion 411 includes a heat dissipation surface 430, and the heat dissipation surface 430 further includes: a first side 431 facing away from the surface 421; and a second side 432 connected to the surface 421. Moreover, on two opposite sides of the surface 421 defining the through hole 412, two such protrusions 411 are provided. The first side edges 431 of the protrusions 411 on the two opposite sides of the through hole 412 are not connected to each other, so that the through hole 412 is formed in an open state to allow air to circulate.

In the energy storage system 200, when the impedance of the battery cells 221 of the battery module 220a is smaller than the impedance of the battery cells 221 of the other battery module 220b, a high-density current flows to the battery module 220a. According to the present invention, the through-holes 412 are used to reduce the width of the current path of the conductive sheet 224a and adjust the impedance value of the conductive sheet 224a. Compared with the structure using power devices, no local temperature rise is caused. In addition, the protrusions 411 are also used to dissipate heat at the same time to avoid temperature rise and reach To the best design. In the foregoing embodiments, since the area of the heat dissipation surface 430 in the embodiment of FIG. 8A is the largest, the heat dissipation effect is the best.

In summary, according to an embodiment of the present invention, the conductive sheet 224a of the battery module 220a is provided with a plurality of protrusions 411 and a plurality of through holes 412. The through hole 412 can shorten the width of the current path of the conductive sheet 224a. The protrusion 411 can provide a heat dissipation function and reduce the temperature rise effect caused by the increase in impedance. According to another embodiment, in the energy storage system 200, the width of the current path of the first conductive sheets 224a of the first battery module 220a is different from the width of the second conductive sheets 224b of the second battery module 220b The width of the current path. Therefore, the overall impedance of the battery module 220a and the other battery module 220b can be matched with each other through the conductive sheet, and the installation of power components can be increased without additional cost. Moreover, the conductive sheets 224a with higher impedance are evenly distributed and will not concentrate the heat locally, causing the local temperature to be too high. The conductive sheets 224a directly contact the battery cells 221, so that the overall heat can pass through the battery cells 221. The battery cells 221 are further dispersed.

241a‧‧‧Slotting

245‧‧‧electrode end

246‧‧‧Connecting channel part

411‧‧‧Protrusion

412‧‧‧Through hole

421‧‧‧surface

430‧‧‧Radiating surface

431‧‧‧First side

432‧‧‧Second side

433‧‧‧ third side

439‧‧‧Open

Claims (12)

A battery module includes: a plurality of battery cores; and at least one conductive sheet, electrically connected to the battery cores, including: a surface; and a plurality of protrusions formed on the surface and protruding from the surface Wherein, a plurality of through holes are formed on the surface to shorten the width of the current path of the at least one conductive sheet. The battery module according to claim 1, wherein each of the protrusions includes a heat dissipation surface, and the heat dissipation surface includes: a first side edge defining an opening; and a second side edge connected to the surface . The battery module according to claim 2, wherein the heat dissipation surface further includes a third side connected to the surface, and one end of the second side and the third side connected to the first side, And the other ends of the second side and the third side are connected to each other, and the cross section of the heat dissipation surface facing the first side has an area closer to the first side than the area farther from the The cross-sectional area of the first side. The battery module according to claim 3, wherein the other end of the second side and the third side of the heat dissipation surface is connected to a point, and the opening faces a first direction, and the first The direction is not parallel to the normal direction of the surface. The battery module according to claim 4, wherein the heat dissipation surface of each of the protrusions forms a half cone shape. The battery module according to claim 2, wherein: Among the sections of the heat dissipation surface facing the first side, the area of the section closer to the first side is smaller than the area of the section farther from the first side. The battery module according to claim 6, wherein the opening faces a first direction, and the first direction is parallel to the normal direction of the surface. The battery module according to claim 2, wherein the heat dissipation surface includes: a third side edge defining another opening and facing the first side edge; and a fourth side edge connected to the The surface is opposite to the second side. The battery module according to claim 8, wherein the opening faces a first direction and the other opening faces a second direction, and neither the first direction nor the second direction is parallel to the normal line of the surface direction. The battery module according to claim 1, wherein each of the protrusions includes a heat dissipation surface, and the heat dissipation surface further includes: a first side edge facing away from the surface; and a second side edge connected to On the surface, and on the two opposite sides of the surface defining the through hole, two such protrusions are provided. The battery module according to any one of claims 1 to 10, wherein at least one conductive sheet includes a plurality of electrode ends and a plurality of connecting channel parts, each of the connecting channel parts is connected to two adjacent ones of the electric Between the extreme parts, the protruding part and the through holes are arranged in each connecting channel part. An energy storage system, comprising: a battery module as described in any one of claims 1 to 11; and another battery module comprising: a plurality of other battery cells and at least another conductive sheet arranged in the other The two ends of a battery cell are used to connect the other battery cells in series or in parallel.

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