A battery pack temperature control device for a new energy bus

Abstract

This invention relates to a temperature control device for a battery pack in a new energy bus, comprising a battery box, several module boxes arranged side-by-side in the middle of the inner side of the battery box, several battery cells arranged side-by-side in the module boxes, a heat spreader plate embedded in one inner wall of one side of the module box, several heat exchange tubes embedded inside the module box and abutting against the heat spreader plate, an insulation tank on one side of the outer side of the battery box, a heat exchanger on one side of the insulation tank, and an air conditioner on one side of the heat exchanger. The air conditioner is connected to the heat exchanger and the insulation tank respectively through refrigerant pipes. A water pump is installed at one end of the insulation tank. In winter or low-temperature environments, it collects heat from the air, heating the water in the insulation tank to hot water. In summer or high-temperature environments, it releases heat to the air through the heat exchanger and cools the water in the insulation tank to cold water, so that the battery cells can be maintained between 20 and 30 degrees Celsius in various temperature environments, so that the working efficiency of the battery cells can be optimized.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and specifically to a temperature control device for a battery pack used in new energy buses. Background Technology

[0002] Lithium-ion batteries require thermal management during application. When lithium-ion batteries are used in environments with large temperature variations or under conditions where the battery generates a lot of heat, they need to be heated or cooled to ensure that the lithium ions operate within the set temperature range and avoid safety risks and rapid degradation of the lithium-ion battery life.

[0003] Patent document CN112234288A discloses a battery pack for lithium battery temperature equalization, including a battery management module, an upper outer shell, and a lower outer shell. Between the upper and lower outer shells are a cell assembly, a heating film, a liquid cooling plate, and a temperature sensor. The cells within the cell assembly are spaced between the upper and lower outer shells. Each cell is equipped with a heating film and a liquid cooling plate, and the liquid cooling plate is covered with an insulating plate. This invention employs a distributed heating and cooling design, allowing for individual heating or cooling of each cell within the battery pack. It also allows for heating some cells while cooling others, achieving precise temperature control of individual cells, high temperature equalization efficiency, and ensuring long-term uniform cell temperature, thus extending the battery pack's lifespan.

[0004] The above-mentioned device has the following shortcomings: When in use, the device simply heats or cools each battery cell by supplying high-temperature or low-temperature refrigerant through a liquid cooling plate. The temperature changes are drastic and the refrigerant supply is difficult to coordinate, making it difficult for each battery cell to heat up or cool down evenly. It is also easy for the heating or cooling to be too rapid, which limits the working efficiency of the battery cells. The above-mentioned device does not take into account the overall temperature maintenance when in operation, and requires additional energy to maintain the temperature of the battery cells, which is not energy-efficient. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned problems and deficiencies by providing a temperature control device for battery packs in new energy buses, thereby improving overall work efficiency.

[0006] The technical problem solved by this invention is:

[0007] (1) When the above device is used, it simply delivers high-temperature or low-temperature refrigerant through the liquid cooling plate to heat or cool each cell. The temperature changes drastically and the refrigerant delivery is difficult to coordinate, making it difficult for each cell to heat up or cool down evenly. It is also easy to cause the cell to heat up or cool down too quickly, which limits the working efficiency of the cell.

[0008] (2) The above device does not take into account the overall temperature maintenance when it is working, and requires additional energy to maintain the temperature of the battery cell, which is not energy-efficient.

[0009] The objective of this invention can be achieved through the following technical solution: A battery pack temperature control device for new energy buses includes a battery box, several module boxes arranged side by side in the middle of the inner side of the battery box, several battery cells arranged side by side in the module boxes, a heat spreader plate embedded in the inner wall of one side of the module box, several heat exchange tubes embedded inside the module box and abutting against the heat spreader plate, an insulation tank provided on one side of the outer side of the battery box, a heat exchanger provided on one side of the insulation tank, an air conditioner provided on one side of the heat exchanger, the air conditioner being connected to the heat exchanger and the insulation tank respectively through refrigerant pipes, and a water pump installed at one end of the insulation tank.

[0010] As a further embodiment of the invention, a third distributor is embedded inside both ends of the module box, and a first connecting pipe is installed at both ends of the module box. One side of the third distributor is connected to the first connecting pipe, and the other side of the third distributor is connected to the heat exchange pipe.

[0011] As a further aspect of the invention, a first shunt is provided on the inner side of both ends of the battery box. One side of the first shunt is connected to the module box through each first connecting pipe. A second connecting pipe is connected through the end of the first shunt near the heat preservation tank. The second connecting pipe passes through the side wall of the battery box, and a second shunt is connected through the end of the second connecting pipe outside the battery box.

[0012] As a further aspect of the invention, the insulated tank is connected to one of the second connecting pipes via a second distributor, and the water pump is connected to the other second connecting pipe via a second distributor.

[0013] As a further aspect of the invention, a filling pad is provided on the side of the module box away from the heat exchange tube and between the battery cell and the inner wall of the module box, and a limiting spring is provided between the inner wall of one end of the module box and one side of the battery cell.

[0014] As a further aspect of the invention, a heat exchange cavity is provided in the middle of the inner side of the heat exchange plate, and a working fluid copper mesh is filled between the heat exchange cavity and the inner wall of the heat exchange plate, with a heat-conducting working fluid adsorbed in the working fluid copper mesh.

[0015] As a further aspect of the invention, the heat exchange plate has several equally spaced and uniformly distributed arc-shaped grooves arranged side by side on the side near the heat exchange tubes, and the heat exchange tubes correspond one-to-one with the arc-shaped grooves, with the cross-section of the arc-shaped grooves being semi-circular.

[0016] As a further aspect of the invention, a first heat insulation pad is embedded inside the module box, and the first heat insulation pad covers the outer periphery of the heat exchange tube and the filling pad.

[0017] As a further aspect of the invention, the bottom of the arc-shaped groove and the heat exchange tube are filled with thermally conductive liquid metal, and a second heat insulation pad is installed between the outer side of the heat exchange tube and the inner sidewall of the module box, with the second heat insulation pad disposed inside the first heat insulation pad.

[0018] The beneficial effects of this invention are:

[0019] (1) By arranging the battery cells in a modular, side-by-side manner through module boxes, users can easily set the voltage, current, and other electrical values ​​of a single module. This allows for the setting of different numbers of modules according to different needs, i.e., the installation of different numbers of module boxes. This enables rapid preparation of the battery pack according to different requirements. During operation, in winter or low-temperature environments, the air conditioner and heat exchanger are activated based on the real-time temperature of the battery. The air conditioner uses the heat exchanger to collect heat from the air and heats the refrigerant in the refrigerant pipes to a high-temperature refrigerant. At the same time, the heat of the high-temperature refrigerant is stored in the water inside the insulated tank through the refrigerant pipes installed inside the insulated tank. In the process, the water in the insulation tank is heated to hot water, and then the water pump delivers the hot water from the insulation tank to each heat exchange tube in the module box. The heat exchanger heats each battery cell evenly, so that the battery cell can be maintained between 20 and 30 degrees Celsius in winter or low temperature environments. In summer or high temperature environments, the heat exchanger releases heat into the air and cools the water in the insulation tank to cold water, thereby cooling each battery cell evenly. This allows the battery cell to be maintained between 20 and 30 degrees Celsius in various temperature environments, so that the battery cell can achieve the best working efficiency.

[0020] (2) Hot or cold water is introduced into the third distributor through the first connecting pipe. The third distributor evenly introduces hot or cold water into each heat exchange tube, thereby ensuring that the heat spreader is heated or cooled evenly. This ensures that each battery cell is heated or cooled evenly, avoiding uneven heating of the battery cells and thus improving the consistency of battery cell discharge and service life. It also facilitates targeted management of each battery cell by the user. Water is introduced into or out of the battery box through the second connecting pipe. The first distributor evenly delivers hot or cold water to each module box. After heat exchange, the water is collected centrally. The second distributor enables one set of air conditioning and insulation tank to deliver hot or cold water to multiple battery boxes. This allows the user to set up different numbers of battery boxes on the bus according to different needs, and ensures that each battery cell in each battery box can work within the optimal temperature range, achieving the best working efficiency and service life. The filling pad provides elastic support for the battery cells, which can accommodate battery cells of different sizes and adapt to different needs. The expansion of the battery cell during use protects the cell, and the limiting spring provides auxiliary elastic support, further stabilizing the cell within the module housing. A foam-filled pad is placed between the cell and the module housing, making it easy to remove and refill, facilitating reuse and maintenance, and reducing usage difficulty. Heat conduction is achieved through a heat spreader, allowing for face-to-face heat transfer rather than linear sequential heat transfer through pipes. This ensures uniform and synchronous heating and cooling of the cells within the module housing, enabling users to control cell temperature more evenly. A first insulation pad isolates heat conduction between the inside and outside of the module housing, maintaining cell temperature in low-temperature winter environments, reducing cooling rate, improving energy efficiency, and making the entire device more energy-efficient. An arc-shaped groove increases the contact area between the heat exchange tube and the heat spreader, maximizing heat exchange efficiency. Thermally conductive liquid metal improves the thermal conductivity between the heat spreader and the heat exchange tube. A second insulation pad reduces heat conduction from the heat exchange tube to the module housing, minimizing heat loss. Attached Figure Description

[0021] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0022] Figure 1 This is a top view of the overall structure of the present invention;

[0023] Figure 2 This is a top view of the internal structure of the module box of the present invention;

[0024] Figure 3 for Figure 2 A sectional view of section AA in the middle;

[0025] Figure 4 This is a front view of the overall structure of the heat spreader of the present invention;

[0026] In the diagram: 1. Battery box; 2. Module box; 3. First distributor; 4. First connecting pipe; 5. Second connecting pipe; 6. Insulation tank; 7. Heat exchanger; 8. Air conditioner; 9. Refrigerant pipe; 10. Water pump; 11. Second distributor; 12. Third distributor; 13. Heat exchange tube; 14. Heat spreader; 15. Filler pad; 16. Limiting spring; 17. First heat insulation pad; 18. Working fluid copper mesh; 19. Heat exchange chamber; 20. Arc-shaped groove; 21. Thermal conductive liquid metal; 22. Second heat insulation pad. Detailed Implementation

[0027] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0028] Please see Figure 1-4 As shown: A temperature control device for a battery pack in a new energy bus includes a battery box 1. Several module boxes 2 are arranged side by side in the middle of the inner side of the battery box 1. Several battery cells are arranged side by side in the module boxes 2. A heat spreader plate 14 is embedded in the inner wall of one side of the module box 2. Several heat exchange pipes 13 are embedded inside the module box 2 and abut against the heat spreader plate 14. An insulation tank 6 is provided on the outer side of the battery box 1. A heat exchanger 7 is provided on one side of the insulation tank 6. An air conditioner 8 is provided on one side of the heat exchanger 7. The air conditioner 8 is connected to the heat exchanger 7 and the insulation tank 6 respectively through a refrigerant pipe 9. A water pump 10 is installed at one end of the insulation tank 6.

[0029] In this embodiment, the battery cells are arranged in a modular, side-by-side configuration using module boxes 2. This allows users to easily set the voltage and current values ​​of individual modules, enabling the installation of different numbers of modules (i.e., different numbers of module boxes 2) to quickly prepare the battery pack according to various needs. During operation, in winter or low-temperature environments, the air conditioner 8 and heat exchanger 7 are activated based on the real-time battery temperature. The air conditioner 8 collects heat from the air using the heat exchanger 7 and heats the refrigerant in the refrigerant pipe 9 to a high-temperature refrigerant. Simultaneously, the heat from the high-temperature refrigerant is stored in the insulation tank 6 through the refrigerant pipe 9 installed inside the insulation tank 6. In the water, the water in the insulation tank 6 is heated to hot water. Then, the water pump 10 delivers the hot water from the insulation tank 6 to each heat exchange tube 13 in the module box 2. The heat spreader 14 heats each battery cell evenly, so that the battery cell can be maintained between 20 and 30 degrees Celsius in winter or low temperature environments. In summer or high temperature environments, the heat exchanger 7 releases heat into the air and cools the water in the insulation tank 6 to cold water, thereby uniformly cooling each battery cell. This allows the battery cell to be maintained between 20 and 30 degrees Celsius in various temperature environments, so that the battery cell can achieve the best working efficiency.

[0030] Both ends of the module box 2 are equipped with a third distributor 12, and both ends of the module box 2 are equipped with a first connecting pipe 4. One side of the third distributor 12 is connected to the first connecting pipe 4, and the other side of the third distributor 12 is connected to the heat exchange tube 13. During operation, hot or cold water is introduced into the third distributor 12 through the first connecting pipe 4. The third distributor 12 evenly introduces the hot or cold water into each heat exchange tube 13, thereby making the heat spreader 14 uniformly heated or cooled. This ensures that each battery cell is uniformly heated or cooled, avoids uneven heating of the battery cells causing uneven performance, improves the consistency of battery cell discharge and service life, and facilitates users to manage each battery cell in a targeted manner.

[0031] A first distributor 3 is provided on the inner side of both ends of the battery box 1. One side of the first distributor 3 is connected to the module box 2 through a first connecting pipe 4. A second connecting pipe 5 is connected to the end of the first distributor 3 near the heat preservation tank 6. The second connecting pipe 5 passes through the side wall of the battery box 1, and a second distributor 11 is connected to the end of the second connecting pipe 5 outside the battery box 1. The heat preservation tank 6 is connected to one of the second connecting pipes 5 through the second distributor 11, and the water pump 10 is connected to the other second connecting pipe 5 through the second distributor 11. During operation, water is introduced into or drawn out of the battery box 1 through the second connecting pipe 5, and hot or cold water is evenly delivered to each module box 2 through the first distributor 3. After heat exchange, the water is collected centrally. The second distributor 11 enables an air conditioner 8 and a heat preservation tank 6 to deliver hot or cold water to multiple battery boxes 1. This allows users to install different numbers of battery boxes 1 on the bus according to different needs, and ensures that each cell in each battery box 1 can work within the optimal temperature range, achieving the best working efficiency and service life.

[0032] A filling pad 15 is placed between the battery cell and the inner wall of the module box 2 on the side away from the heat exchange tube 13. A limiting spring 16 is provided between the inner wall of one end of the module box 2 and one side of the battery cell. One end of the limiting spring 16 is fixedly connected to the module box 2, and the other end of the limiting spring 16 abuts against the battery cell. During operation, the filling pad 15 provides elastic support for the battery cell, which can accommodate battery cells of different sizes and the expansion of the battery cell during use, thereby protecting the battery cell. The limiting spring 16 provides auxiliary elastic support for the battery cell, further stabilizing the battery cell within the module box 2. The filling pad 15 is filled between the battery cell and the module box 2 using a foam filling process, making it easy to remove and refill, thus facilitating reuse and maintenance and reducing the difficulty of use.

[0033] A heat exchange cavity 19 is provided in the middle of the inner side of the heat exchange plate 14. A working fluid copper mesh 18 is filled between the heat exchange cavity 19 and the inner wall of the heat exchange plate 14. The working fluid copper mesh 18 adsorbs the heat-conducting working fluid. During heat exchange, when the side of the heat exchange plate 14 closest to the heat exchange tube 13 is the hot end, the working fluid copper mesh 18 on the side closest to the heat exchange tube 13 absorbs heat, evaporating the working fluid from liquid to gas. The gaseous working fluid passes through the heat exchange cavity 19 and condenses and releases heat on the working fluid copper mesh 18 on the side closest to the battery cell. Guided by the working fluid copper mesh 18, the liquid working fluid is then transported away from the heat exchange plate 14. The heat is guided to the hot end and evaporates again, repeating the cycle to quickly conduct heat and heat the battery cell, preventing it from being damaged by excessive cooling. When the side of the heat spreader 14 closest to the battery cell is the hot end, the heat conduction direction is reversed, thereby controlling the temperature of the battery cell and cooling it down. At the same time, the heat is conducted face-to-face through the heat spreader 14 instead of linearly and sequentially through pipes, so that the battery cells in the module box 2 can be heated or cooled down uniformly and synchronously, making it easier for users to control the temperature of the battery cells more evenly.

[0034] The heat exchange plate 14 has several equally spaced and uniformly distributed arc-shaped grooves 20 arranged side by side on the side near the heat exchange tube 13, and the heat exchange tube 13 corresponds to the arc-shaped groove 20 one by one. The cross-section of the arc-shaped groove 20 is semi-circular. The arc-shaped groove 20 increases the contact surface between the heat exchange tube 13 and the heat exchange plate 14, thereby making the heat exchange efficiency more complete and reducing heat loss.

[0035] The module box 2 is equipped with a first heat insulation pad 17, which covers the heat exchange tube 13 and the filling pad 15. The first heat insulation pad 17 isolates the heat conduction inside and outside the module box 2, so that the battery cell can maintain its temperature in the low temperature environment in winter, reduce the cooling rate, improve energy utilization, and make the whole device more energy-efficient.

[0036] The bottom of the arc-shaped groove 20 and the heat exchange tube 13 are filled with thermally conductive liquid metal 21. A second heat insulation pad 22 is installed between the outer side of the heat exchange tube 13 and the inner side wall of the module box 2. The second heat insulation pad 22 is set inside the first heat insulation pad 17. The thermally conductive liquid metal 21 improves the heat conduction efficiency between the heat spreader 14 and the heat exchange tube 13. The second heat insulation pad 22 reduces the heat conduction from the heat exchange tube 13 to the module box 2, further reducing heat loss.

[0037] In use, the battery cells are arranged in a modular, side-by-side configuration using module boxes 2. This allows users to easily set the voltage, current, and other electrical parameters of a single module, enabling the installation of different numbers of modules (i.e., different numbers of module boxes 2) to quickly prepare the battery pack according to various needs. During operation, in winter or low-temperature environments, the air conditioner 8 and heat exchanger 7 are activated based on the real-time battery temperature. The air conditioner 8 collects heat from the air using the heat exchanger 7 and heats the refrigerant in the refrigerant pipe 9 to a high-temperature refrigerant. Simultaneously, the heat from the high-temperature refrigerant is stored in the insulation tank 6 via the refrigerant pipe 9 installed inside the insulation tank. The water in the insulation tank 6 is heated to hot water. Then, the water pump 10 delivers the hot water from the insulation tank 6 to each heat exchange tube 13 in the module box 2. The heat exchange plate 14 heats each battery cell evenly, so that the battery cell can be maintained between 20 and 30 degrees Celsius in winter or low temperature environment. In summer or high temperature environment, the heat exchanger 7 releases heat into the air and cools the water in the insulation tank 6 to cold water, thereby cooling each battery cell evenly. This allows the battery cell to be maintained between 20 and 30 degrees Celsius in various temperature environments, so that the working efficiency of the battery cell can reach the optimal level.

[0038] Hot or cold water is introduced into the third distributor 12 through the first connecting pipe 4. The third distributor 12 then evenly distributes the hot or cold water into each heat exchange tube 13, thereby ensuring that the heat spreader 14 is uniformly heated or cooled. This ensures uniform heating or cooling of each battery cell, preventing uneven heating that could lead to performance inconsistencies, improving the consistency of cell discharge and lifespan, and facilitating targeted management of each battery cell by the user. Water is introduced into or out of the battery box 1 through the second connecting pipe 5. The first distributor 3 evenly distributes the hot or cold water into each module box 2, where it is collected after heat exchange. The second distributor 11 allows one air conditioner 8 and insulation tank 6 to supply hot or cold water to multiple battery boxes 1, enabling users to install different numbers of battery boxes 1 on the bus according to different needs. This ensures that each battery cell in each battery box 1 operates within its optimal temperature range, achieving optimal efficiency and lifespan. The filling pad 15 provides elastic support for the battery cells, accommodating different sizes of cells and adapting to various usage conditions. The expansion during the process protects the battery cell, and the limiting spring 16 provides auxiliary elastic support for the battery cell, further stabilizing it within the module box 2. The filling pad 15, filled between the battery cell and the module box 2 using a foam filling process, is easy to remove and refill, facilitating reuse and maintenance and reducing the difficulty of use. Heat is conducted face-to-face through the heat spreader 14, rather than linearly through pipes, allowing the battery cells within the module box 2 to heat up or cool down uniformly and synchronously, thus providing users with more even heating and cooling. The temperature of the battery cell is uniformly controlled. The first heat insulation pad 17 isolates the heat conduction inside and outside the module box 2, so that the battery cell can maintain its temperature in the low temperature environment of winter, reduce the cooling rate, improve energy utilization, and make the whole device more energy-efficient. The arc groove 20 increases the contact surface between the heat exchange tube 13 and the heat spreader 14, thereby making the heat exchange efficiency more complete. The heat conduction liquid metal 21 improves the heat conduction efficiency between the heat spreader 14 and the heat exchange tube 13. The second heat insulation pad 22 reduces the heat conduction from the heat exchange tube 13 to the module box 2, thereby reducing heat loss.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A temperature control device for a battery pack in a new energy bus, comprising a battery box (1), characterized in that, The battery box (1) has several module boxes (2) arranged side by side in the middle of its inner side. Several battery cells are arranged side by side in the module box (2). A heat spreader (14) is embedded in the inner wall of one side of the module box (2). Several heat exchange tubes (13) are embedded inside the module box (2), and the heat exchange tubes (13) abut against the heat spreader (14). A heat preservation tank (6) is provided on the outer side of the battery box (1). A heat exchanger (7) is provided on one side of the heat preservation tank (6). An air conditioner (8) is provided on one side of the heat exchanger (7). The air conditioner (8) is connected to the heat exchanger (7) and the heat preservation tank (6) respectively through a refrigerant pipe (9). A water pump (10) is installed at one end of the heat preservation tank (6). The heat exchange chamber (19) is provided in the middle of the inner side of the heat exchange plate (14). A working medium copper mesh (18) is filled between the heat exchange chamber (19) and the inner wall of the heat exchange plate (14). The working medium copper mesh (18) is adsorbed with a heat-conducting working medium. The heat exchange plate (14) has several equally spaced and uniformly distributed arc-shaped grooves (20) arranged side by side on the side near the heat exchange tube (13), and the heat exchange tube (13) corresponds one-to-one with the arc-shaped grooves (20). The cross section of the arc-shaped grooves (20) is semi-circular. The module box (2) is equipped with a first heat insulation pad (17) embedded inside, and the first heat insulation pad (17) covers the outer periphery of the heat exchange tube (13) and the filling pad (15); The bottom of the arc-shaped groove (20) and the heat exchange tube (13) are filled with heat-conducting liquid metal (21). A second heat insulation pad (22) is installed between the outer side of the heat exchange tube (13) and the inner side wall of the module box (2). The second heat insulation pad (22) is located inside the first heat insulation pad (17).

2. The battery pack temperature control device for new energy buses according to claim 1, characterized in that, The module box (2) has a third distributor (12) embedded inside both ends. The module box (2) has a first connecting pipe (4) installed at both ends. One side of the third distributor (12) is connected to the first connecting pipe (4), and the other side of the third distributor (12) is connected to the heat exchange pipe (13).

3. The battery pack temperature control device for new energy buses according to claim 1, characterized in that, The battery box (1) is provided with a first splitter (3) on the inner side of both ends. One side of the first splitter (3) is connected to the module box (2) through each first connecting pipe (4). The end of the first splitter (3) near the heat preservation tank (6) is connected to a second connecting pipe (5). The second connecting pipe (5) penetrates the side wall of the battery box (1), and the end of the second connecting pipe (5) outside the battery box (1) is connected to a second splitter (11).

4. The battery pack temperature control device for new energy buses according to claim 3, characterized in that, The insulated tank (6) is connected to one of the second connecting pipes (5) through the second distributor (11), and the water pump (10) is connected to the other second connecting pipe (5) through the second distributor (11).

5. The battery pack temperature control device for new energy buses according to claim 1, characterized in that, The module box (2) is filled with a filling pad (15) on the side away from the heat exchange tube (13) and between the battery cell and the inner wall of the module box (2). A limiting spring (16) is provided between the inner wall of one end of the module box (2) and one side of the battery cell.

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