Patent Publication Number: US-2018040864-A1

Title: Battery pack for a handheld machine tool

Description:
FIELD 
     The present invention relates to a battery pack for a handheld machine tool. 
     BACKGROUND INFORMATION 
     Generally, electrical handheld machine tools such as impact wrenches, drilling machines, angle grinders, jigsaws, circular saws or planing machines for the craftsmen or do-it-yourselfer use either an alternating current motor or a direct current motor as drive motor. While the former is usually supplied with an alternating current from the grid via a mains cable, the electrical energy for the supply of the direct current motor normally comes from what is known as a battery pack, i.e., a rechargeable accumulator in a housing that is able to be coupled with the housing of the handheld machine tool and is electrically connected to the current supply lines of the direct current motor when the two housings are coupled. 
     Such conventional battery packs include rechargeable accumulators, normally a plurality of battery cells connected in a parallel and/or series circuit. Herein, such a battery pack therefore denotes a battery pack that is preferably made up of a plurality of electrically interconnected battery cells. This battery pack is able to store electrical energy, supplies the energy for the operation of the handheld machine tool, and is accommodated in an exchangeable manner in a chamber, an interface or the like of the handheld machine tool. The allocation of the battery pack to the handheld machine tool is implemented by inserting or sliding the battery pack into a complementary insert bushing of the device housing. The battery pack is able to be coupled with the device housing of the handheld machine tool in such a way that the electric tool is electrically coupled with the battery pack and mechanically locked when the two housings are coupled. The electrical contacting normally takes place in the region of the locking device. 
     The battery packs have the disadvantage that each battery cell experiences heat losses both during the current delivery and the current draw, which may lead to an increased temperature of the entire battery block. To prevent damage to the battery cell and/or the battery block, heat losses must be dissipated in a reliable manner on the one hand, and heating of the battery pack at low outside temperatures must be possible on the other, which is advantageous especially in the case of cells that are chemically based on lithium. 
     In addition, such battery packs have housings that are made of plastic materials for the most part. Plastic materials generally used for battery pack housings include acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC), or polyamide (PA). These plastic materials have excellent mechanical properties and adequate thermal conductivity, which makes them suitable for use as battery pack housings for most of the battery cells that are currently on the market, such as lithium-ion cells. However, these have the disadvantage of providing good thermal insulation. This is not desired in a battery pack inasmuch as the heat created during the operation or charging of the battery pack is to be dissipated as quickly as possible. 
     Moreover, the development of more recent battery packs goes in the direction of a greater power output, meaning that the heat losses are becoming greater as well; as a result, more heat is generated in the interior of the housing and must be dissipated into the environment more rapidly so as to avert overheating of the battery cells. 
     In addition, more and more battery pack housings are developed in tightly sealed form for the most part in order to prevent the entry of moisture, which means that the heat dissipation must take place through the wall of the housing. 
     SUMMARY 
     It is an object of the present invention to mitigate the aforementioned disadvantages and to provide a battery pack for a handheld machine tool that features a more optimal dissipation of the generated heat losses. The battery pack according to the present invention may also offer excellent ergonomics and assembly capabilities and have a cost-effective and uncomplicated structure. 
     Advantageous refinements, variants and further developments of the present invention are described herein. 
     According to the present invention, an example battery pack for a handheld machine tool includes a cell holder and at least one battery cell; the cell holder accommodates the at least one battery cell, and the battery cell has a lateral area that extends parallel to a longitudinal axis x. The lateral area is delimited by two end faces disposed at a right angle to longitudinal axis x, at which the electrical poles of the battery cell are situated. At least one elastic, heat-conductive insert is disposed between at least one end face of the battery cell and a wall of the battery pack housing extending essentially parallel to the end face of the battery cell. The elastic, heat-conductive insert is in thermal contact with the end face of the battery cell and dissipates heat from the battery cell in the direction of the wall of the battery pack housing. It is advantageously provided that the elastic, heat-conductive insert is situated between the end face of the battery cell and a wall of the battery pack housing that is situated essentially at a right angle to longitudinal axis x of the battery cell. 
     In one particularly preferred specific embodiment of the present invention, at least one heat distribution element is disposed between the at least one elastic, heat-conductive insert and the wall of the battery pack housing, in the region of the at least one end face of the at least one battery cell. The heat distribution element is in thermal contact with the elastic, heat-conductive insert and with the wall of the battery pack housing and ensures an even application of heat to the wall of the battery pack housing. 
     It may be advantageous to produce the at least one heat-conductive insert at least partially from a thermally conductive material that belongs to at least one of the material groups of elastomers, thermo-plastic elastomers, or carbon fibers. The plastic materials such as acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC), or polyamide (PA), e.g., PA6 or PA12, usually have good mechanical properties and an adequate thermal conductivity of 0.17 W/mK (ABS), 0.21 W/mK (PC), and 0.29 W/mk (PA6). This makes them suitable for use as battery pack housings for most of the battery cells that are currently on the market. According to the present invention, the heat-conductive insert has a thermal conductivity that is greater than 0.15 W/mK, and preferably greater than 0.20 W/mK, and most preferably, lies between 0.20 W/mK and 0.50 W/mK. If the thermally conductive insert has a wall thickness of less than 1 mm, the thermal conductivity may also be less than 0.15 W/mK, and preferably may amount to exactly 0.15 W/mK. Preferably, the heat-conductive insert has a Shore hardness of less than 50 Shore A, and preferably of between 20 Shore A and 45 Shore A. 
     According to an example embodiment of the present invention, the heat distribution element is at least partially made of a metal, preferably an aluminum or a magnesium alloy, or of a heat-conducting plastic. The heat distribution element advantageously is a planar component having a length L, a width B, and a thickness D. Thickness D is small in comparison with length L and width B, and heat distribution element has a plurality of recesses distributed across its surface. This makes it possible to dissipate the heat to be carried away in an especially advantageous manner such that it is distributed across the battery pack housing. 
     In one preferred specific embodiment, the heat distribution element is developed as a metal foil having a thickness of between 0.1 mm and 0.5 mm, and preferably of between 0.01 mm and 0.3 mm, or it is developed as a graphite layer at a thickness of between 0.1 mm and 0.5 mm, and preferably of between 0.01 mm and 0.1 mm. 
     Therefore, it is especially advantageous if the heat-conductive insert is developed as an elastic foil having a thickness of between 0.1 mm and 1.4 mm, preferably of between 0.2 mm and 1.2 mm, and most preferably, of between 0.3 mm and 1.0 mm. This is advantageously in particular if the heat-conductive insert and the heat distribution element are developed as a composite part, and especially as a foil composite part. 
     In an advantageous manner, the cell holder at least regionally forms an outer side of the first housing component and/or the second housing component of the battery pack housing. In an especially preferred specific embodiment, the cell holder forms the second housing component in its entirety. Here, the battery pack housing preferably has at least two side components, which keep the first housing component and the second housing component together in the assembled state of the battery pack in such a way that a detachment of the first housing component from the second housing component, or vice versa, is prevented. 
     In this context it is possible that the side components are at least partially made from a metal, preferably an aluminum or a magnesium pressure casting. In this case, a reliable insulation insert has to be used between the battery cells and the side components; it is possible, for example, to use the elastic, heat-conductive insert as insulation inserts. 
     In another further development of the present invention, the battery pack has two elastic heat-conductive inserts. A heat-conductive insert together with a side component is produced by a 2K injection molding method in each case, preferably in a common working step and in integrated form, in particular. It is advantageous here if the side components are made of the same material as the rest of the battery pack housing, preferably a polyamide. 
     The cell holder advantageously accommodates two or more battery cells, which are connected by at least one cell connector in a parallel and/or series circuit. The at least one cell connector is situated between an end face of the battery cells and the elastic, heat-conductive insert. 
     The at least one cell connector advantageously connects at least two or more battery cells, and preferably four battery cells, and most preferably, six battery cells to one another. In a preferred embodiment variant, the cell connector has a large surface such that the cell connector essentially covers the end faces of the battery cells that are connected to each other, and in this way assumes the function of the heat distribution element. It is possible in this context that the heat distribution element and the cell connector are developed as a composite part, and as an integrally developed composite part, in particular. In areas in which no heat transfer is desired and in which a heat transfer is to be prevented as far as possible, the cell connector includes slot-type recesses, so that the heat losses transferred from the battery cells to the cell connectors in a pointwise manner are able to be distributed to the entire surface and are transferred to the elastic element and/or to the side components. In an especially advantageous further development, the elastic, heat-conductive insert is at least regionally in direct thermal contact with the cell connectors. 
     The battery pack according to the present invention may be connected to a handheld machine tool in a detachable manner. Accordingly, provided it is connected to a battery pack according to the present invention, a handheld machine tool constitutes another subject matter of the present invention. The battery pack used in the handheld machine tool is employed as a drive of the handheld machine tool. 
     Lithium-ion cells, in particular, may be used as battery cells because in the case of lithium-ion cells, in particular, it is possible to combine a plurality of battery cells into battery cell blocks in which multiple battery cells are connected in a parallel circuit. It is especially advantageous here that the cell holder is able to accommodate battery cells having different diameters and lengths, thereby allowing the cell holder or the cell carrier to be used in a variety of battery packs. 
     Within the framework of the present application, a handheld machine tool generally denotes all handheld machine tools having a tool carrier that is able to be set into rotation or translation and is able to be driven directly by a drive motor via a transmission or a planetary gear, e.g., straight drills, cordless drills, impact wrenches, multi-function tools, saws, scissors, grinders and/or combination drills, for example. In this context, the transmission of electrical energy is to be understood specifically in such a way that the handheld machine tool is supplied with energy by way of the battery pack. 
     Additional features, application possibilities and advantages of the present invention result from the description of the exemplary embodiments of the present invention below, which are depicted in the figures. It should be noted that the illustrated features are merely of a descriptive nature and may also be used in combination with features of other further developments described in the previous text. They are also not intended to limit the present invention in any shape or form. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in greater detail in the below on the basis of preferred exemplary embodiments, where the same reference numerals have been used for the same features. 
         FIG. 1  shows, by way of example, a view of a handheld machine tool having a battery pack according to the present invention. 
         FIG. 2  shows a perspective representation of a battery pack according to the present invention. 
         FIG. 3  shows a plan view of the battery pack from  FIG. 2 . 
         FIG. 4  shows a perspective exploded view of a first variant of a battery pack according to the present invention. 
         FIG. 5  shows a sectional view of the battery pack from  FIG. 4 . 
         FIG. 6  shows a perspective exploded view of a second variant of a battery pack according to the present invention. 
         FIG. 7  shows sectional view of the battery pack from  FIG. 6 . 
         FIG. 8  shows a detail view of region A from  FIG. 7  with the second variant of the battery pack according to the present invention. 
         FIG. 9  shows a detail view of a third variant of the battery pack according to the present invention. 
         FIG. 10  shows a perspective view of a cell holder having a battery pack electronics system disposed thereon. 
         FIG. 11  shows a perspective detail view of a cutaway from  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
       FIG. 1  shows an electric device that is developed as a handheld machine tool  300 . According to the specific development illustrated, handheld machine tool  300  is able to be mechanically and electrically connected to battery pack  100  for the mains-independent current supply. In  FIG. 1 , handheld machine tool  300  is developed as a cordless combination drill by way of example. However, it is pointed out that the present invention is not restricted to cordless combination drills but may instead be used in different handheld machine tools  300  that are operated using a battery pack  100 . Handheld machine tool  300  has a base body  305 , on which a tool holder  320  is fixed in place; it also has a handle  315  having an interface  380  on which a corresponding interface  180  of a battery pack  100  is situated, in the locked state in this instance. Battery pack  100  is developed as a slide-in battery pack. 
     When battery pack  100  is mounted on handheld machine tool  300 , receiving means provided on handheld machine tool  300 , e.g., guide grooves and guide ribs, are brought into engagement with corresponding guide elements  110  of battery pack  100 . For this purpose, battery pack  100  is inserted in a sliding direction y along the receiving means of handle  315 . Battery pack  100  is slipped into the battery pack receptacle of a handheld machine tool  300  along a lower outer surface  316  of handle  315 , said surface being aligned essentially at a right angle to the longitudinal direction of handle  315 . In the position shown in  FIG. 1 , battery pack  100  is fixed in place on handle  315  of handheld machine tool  300  and locked with the aid of locking means. The locking means include a locking element and an operating element  220 , among others. By actuating operating means  220 , battery pack  100  is able to be detached from handle  315  of handheld machine tool  300 . 
       FIGS. 2 through 5  show a battery pack  100  according to the present invention for a handheld machine tool  300 . Battery pack  100  has a housing  110  which is made up of a first housing component  120  and a second housing component  130 . The housing accommodates at least one, and preferably a plurality (as illustrated here) of battery cells  400  connected in parallel or in series between first housing component  120  and second housing component  130 . Battery cells  400  are preferably positioned between the two housing components  120 ,  130  either with the aid of a cell holder  600  or with the aid of cardboard sleeves in order to insulate battery cells  400  from one another. Battery pack  100  is developed as a slide-in battery pack in the illustrated embodiment variant. 
     For the detachable mounting of battery pack  100  on a handheld machine tool  300  or on a charge device, battery pack  100  is equipped with an interface  180  for a detachable mechanical and electrical connection to a corresponding interface  380  of handheld machine tool  300  or to a corresponding interface of the charge device. When battery pack  100  is mounted, receiving means, e.g., guide grooves and guide ribs, of handheld machine tool  300  or of the charge device, for the accommodation of the corresponding guide elements of battery pack  100 , are brought into an engagement therewith, battery pack  100  being inserted in a contacting direction y along the receiving means, and interface  180  of battery pack  100  being inserted into corresponding interface  380  of handheld machine tool  300  or into the corresponding interface of the charge device. Via interfaces  180 ,  380 , battery pack  100  is able to be allocated to handheld machine tool  300  and/or the charge device. 
     For the locking of battery pack  100  on handle  315 , battery pack  100  is slipped along handle  315  in a sliding direction y, i.e. along a lower outer surface of handle  315  that is aligned essentially at a right angle to the longitudinal direction of handle  315 . In the position shown in  FIG. 1 , battery pack  100  is locked by locking means  200  on handle  315 . Among other things, locking means  200  includes a locking element  210 , which is illustrated only schematically, as well as an operating element  220 . By actuating operating element  220 , battery pack  100  is able to be removed from handle  315  of handheld machine tool  300 . After battery pack  100  has been unlocked, it is able to be separated from handle  315 , i.e., by sliding battery pack  100  counter to sliding direction y along a lower surface of handle  315 . When mounting battery pack  100  on a handheld machine tool  300 , locking element  210  is brought into engagement with a corresponding receptacle (not shown in greater detail) in handle  315  of handheld machine tool  300 . 
     As is shown in  FIG. 3 , interface  180  also encompasses contact elements  140  for the electrical contacting of battery pack  100  with handheld machine tool  300  or the charge device. Contact elements  143  are developed as voltage contact elements and are used as charge and/or discharge contact elements. Contact elements  144  are configured as signal contact elements and are used for the transmission of signals from battery pack  100  to handheld machine tool  300  or to the charge device and/or from handheld machine tool  300  or the charge device to battery pack  100 . 
       FIG. 4  shows a battery pack  100  in the exploded view. It can be seen clearly that battery pack housing  110  has a cell holder  600  having a plurality of battery cells  400 , which are connected in a series circuit. Cell holder  600  is directly formed by second housing component  130 . The connection of the battery cells among one another is realized via cell connector  500 . In addition, it can be gathered that individual battery cells  400  are accommodated at a distance from one another in cell holder  600  for a mechanical fixation. In addition to fixating battery cells  400  in battery pack housing  120 ,  130 , cell holder  600  is also used for cooling battery cells  400  and made from a heat-conducting material, e.g., aluminum or a plastic material. Furthermore, cell holder  600  has sleeve-type insulation walls, so that individual battery cells  400  are separated and an electrical insulation of the individual battery cells  400  from one another is able to be ensured. The heat-transfer resistance between adjacent battery cells  400  and between battery cells  400  and cell holder  600  is as low as possible, so that the heat losses generated by battery cells  400  are able to be dissipated into the external environment in a satisfactory manner, and overheating of the battery pack on the inside is able to be prevented. Fixed in place on the top surface of cell holder  600  within battery pack housing  120 ,  130  is a circuit board of a battery pack electronics system  800 . In addition, the battery pack electronics system includes contact elements  140  for the establishment of the electrical and mechanical connection between battery pack  100  and handheld machine tool  300  or between battery pack  100  and the charge device. Fastening elements, which are not shown in greater detail, ensure the connection between the battery pack electronics system and cell holder  600 . 
     In the specific embodiment shown in  FIG. 4 , battery pack housing  110  also has two side components  125 , although only one of the two side components  125  is shown in  FIG. 4 . Side components  125  keep first housing component  120  and second housing component  130  together in the assembled state in such a way that a detachment of first housing component  120  from second housing component  130 , or vice versa, is prevented. It is advantageous as a matter of principle if cell holder  600  regionally forms an outer side of second housing component  130  or battery pack  100 ; however, as an alternative it is also possible for cell holder  600  to regionally form an outer side of first housing component  120 . It is advantageous in this context if side components  125  are made of the same material as the rest of battery pack housing  110 , preferably of a synthetic, technically usable thermoplastic plastic material such as a polyamide. This makes it possible to reduce costs and to keep the assembly work to a minimum. As an alternative, side components  125  may at least partially be composed of a metal, preferably an aluminum or a magnesium pressure casting. In this case, an adequate or reliable insulation insert, e.g., elastic element  650 , must be used between cell connectors  500  and side components  125 . 
     In addition, cell connectors  500 , by which an electrical connection of battery cells  400  among one another in a parallel and/or series circuit is able to implemented, are shown in  FIG. 4 . Each battery cell  400  has a lateral area  405  that runs parallel to a longitudinal axis x. Lateral area  405  is delimited by two end faces  410  that run at a right angle to longitudinal axis x and at which the electrical poles of battery cells  400  are located. An elastic, heat-conductive insert  650  is situated between end faces  410  of battery cells  400  and a wall of battery pack housing  110  that essentially extends parallel to end faces  410  of battery cells  400 . Elastic, heat-conductive insert  650  is disposed between battery cells  400  and second housing component  130  of battery pack housing  110  in such a way that a thermal contact is created with end faces  410  of battery cells  400 , and heat from battery cells  400  is dissipated in the direction of the wall of battery pack housing  110 . Heat-conductive insert  650  is at least partially made of a heat-conducting material that belongs to at least one of the material groups of elastomers, thermoplastic elastomers or carbon fibers. This makes it possible to ensure that heat-conductive insert  650  has a thermal conductivity that is greater than 0.15 W/mK, and preferably greater than 0.20 W/mK, and most preferably, a thermal conductivity that lies between 0.20 W/mK and 0.50 W/mK on the one hand, and a Shore hardness that is less than 50 Shore A, and preferably lies between 20 Shore A and 45 Shore A on the other. 
     It can furthermore be gathered from  FIG. 4  that a heat distribution element  660  is situated in the region of end faces  410  between elastic, heat-conductive insert  650  and the wall of battery pack housing  110 . Heat distribution element  660  is in thermal contact both with elastic, heat-conductive insert  650  and the wall of battery pack housing  110 , and thus ensures a uniform application of heat to the wall of battery pack housing  110 . Heat distribution element  660  is developed in the form of a planar component that has a length L, a width B, and a thickness D, thickness D being low in comparison with length L and width B. Heat distribution element  660  is made of a metal, preferably an aluminum or a magnesium alloy, or of a heat-conducting plastic material. This makes it possible for heat distribution element  660  to aid in a heat transfer in a region where such a heat transfer is desired. 
     In those regions where the heat transfer is undesired and is to be prevented as much as possible, heat distribution element  660  includes a plurality of recesses  665 . These recesses are distributed across the entire surface of heat distribution element  660 , one recess  665  being provided for each battery cell  400  in the illustrated specific embodiment. This makes it possible to ensure that the heat losses transferred in a pointwise manner from battery cells  400  to elastic element  650 , which is in thermal contact with battery cells  400 , are able to be transferred directly to immediately adjoining heat distribution element  660 , which is in thermal contact with elastic element  650 . Because of recesses  665 , heat distribution element  660  distributes the heat losses, which are transferred in a relatively punctual manner, to the entire surface of respective side components  125  of battery pack housing  110 , heat distribution element  660  also being in direct thermal conduct with respective side component  125 . 
       FIG. 5  represents a sectional view of battery pack  100  according to the present invention. Here, too, it can be seen that cell holder  600  forms second housing component  130  and thus also an outer side of battery pack housing  110 . In addition, it may be gathered from  FIG. 5  that the lateral areas of two battery cells  400  situated next to each other in cell holder  600  do not touch but are mechanically and electrically separated from each other by sleeve-type insulated walls. It can be seen clearly here that elastic, heat-conductive insert  650  is situated between battery cells  400  and a heat distribution element  660 . Heat distribution element  660  is disposed between elastic, heat-conductive insert  650  and one of side components  125  of battery pack housing  110 . This ensures that end faces  410  of battery cells  400 , elastic, heat-conductive insert  650 , heat distribution element  660 , and side component  125  are in thermal contact, so that the heat from battery cells  400  is able to be dissipated in the direction of the wall of battery pack housing  110 . 
       FIG. 6  shows a battery pack  100  in the exploded view. In contrast to battery pack  100  from  FIG. 4 , cell connectors  500  are developed with such a large surface that in addition to their function of ensuring an electrical connection of battery cells  400  among one another in a parallel and/or series circuit, they are also able to assume the function of heat distribution element  660  and aid in the desired heat transfer. It is advantageous in this context that heat distribution element  660  and cell connector  500  are developed as composite parts, and in particular, as an integrally formed composite part; it also has slot-type recesses  665  in the areas in which the heat transfer is not desired and is to be prevented to the greatest extent possible. A separate recess  665  is provided for each battery cell  400 . In this way it can be ensured that the heat losses punctually transferred from battery cells  400  to cell connectors  500  or to heat distribution element  660  are able to be transferred directly to elastic element  650 , which is in thermal contact with cell connectors  500 . Due to recesses  665 , cell connectors  500 , which are developed as heat distribution element  660 , are able to transmit the heat losses, transferred in a relatively punctual manner, to the entire surface and transfer them to elastic element  650 . 
     Elastic element  650  may be in direct thermal contact with respective side component  125 . As can be gathered from  FIG. 6 , elastic, heat-conductive insert  650  is situated directly in side component  125  of battery pack housing  110  or is even produced in one piece with side component  125 . If side components  125  are made from the same material as the rest of battery pack housing  110 , preferably a synthetic, technically usable thermoplastic plastic material such as a polyamide, then this makes it possible to produce heat-conductive insert  650  together with a side component  125  in an injection-molding process, such as a 2K injection molding process, and preferably in a common working step and in one piece, in particular. Costs are able to be reduced in this way, and the assembly work is kept to a minimum. It is advantageous that heat-conductive insert  650  is at least partially made of a heat-conducting material such as an elastomer or a thermoplastic elastomer. Heat distribution element  660  or cell connectors  500  are therefore in thermal contact both with elastic, heat-conductive insert  650  and with the wall of battery pack housing  110 , thereby ensuring a uniform application of heat to the wall of battery pack housing  110 . 
       FIG. 7  represents a sectional view of battery pack  100  from  FIG. 6  according to the present invention. Here, too, it can be gathered that battery pack housing  110  has two side components  125 . In addition, it can be seen there, but especially clearly and in detail in  FIG. 8 , that cell connectors  500  are developed in such a way that they are able to assume the function of heat distribution element  660  and aid in the desired heat transfer to elastic, heat-conductive insert  650 . Elastic, heat-conductive insert  650  is disposed in side components  125  of battery pack housing  110  or, as described in the preceding text, is integrally formed with said side components. This ensures that end faces  410  of battery cells  400 , heat distribution element  660 , elastic, heat-conductive insert  650 , and side component  125  are in thermal contact, so that the heat from battery cells  400  is able to be dissipated in the direction of the wall of battery pack housing  110 . 
       FIG. 9  shows an alternative, third embodiment variant of battery pack  100  according to the present invention. In this specific embodiment, heat-conductive insert  650  and heat distribution element  660  are developed as a composite material, and as a foil composite material, in particular. It is especially advantageous here if heat distribution element  660  is developed as a metal foil having a thickness of between 0.1 mm and 0.5 mm, and preferably of between 0.01 mm and 0.3 mm, or as a graphite layer having a thickness of between 0.1 mm and 0.5 mm, and preferably of between 0.01 mm and 0.1 mm, and if heat-conductive insert  650  is developed as an elastic foil having a thickness of between 0.1 mm and 1.4 mm, and preferably of between 0.2 mm and 1.2 mm, and most preferably, of between 0.3 mm and 1.0 mm. 
     As is clear from  FIG. 6  and especially also from  FIGS. 10 and 11 , in one preferred specific embodiment cell connectors  500  have such a large surface that in addition to their function of ensuring an electrical connection of battery cells  400  among one another in a parallel and/or series circuit, they are also able to assume the function of heat distribution element  660  and aid in the desired heat transfer. It is advantageous here that a cell connector  500  connects at least two battery cells  400 , and preferably four battery cells  400 , or any random number of battery cells to one another in a parallel and/or series circuit. It is clear from  FIGS. 6, 10 and 11  that cell connector  500  is designed to be variable in its specific embodiment and is basically able to be adapted to the specific embodiment of cell holder  600  or to the respective number of battery cells  400 . In the embodiment variant illustrated, cell connectors  500  are developed with a large surface such that end faces  410 , which are connected to one another via a cell connector  500 , are completely covered for the most part. A large-surface specific embodiment of cell connector  500  means that, if it connects two battery cells or four battery cells  400  to one another as shown in  FIGS. 6, 10, and 11 , it largely covers respective end faces  410  of these two battery cells  400  or four battery cells  400 . This makes it possible to ensure that installed cell connectors  500  are able to assume the function of heat distribution element  660 . As an alternative, heat distribution element  660  and cell connector  500  may be developed as a composite part, and as an integrally formed composite part, in particular. 
     In the large-surface cell connectors shown in  FIGS. 6, 10, and 11 , slot-type recesses  665  are likewise situated in regions in which no heat transfer is desired and is to be prevented as far as possible, so that the heat losses punctually transferred from battery cells  400  to cell connectors  500  are able to be transferred directly to elastic element  650 , which is in thermal contact with cell connectors  500 . 
     In addition to the described and illustrated specific embodiments, additional specific embodiments that may encompass additional modifications as well as combinations of features are possible.