Patent Publication Number: US-2023140804-A1

Title: Battery pack, electronic device, and electric tool

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of PCT Application No. PCT/JP2021/031910, filed on Aug. 31, 2021, which claims priority to Japanese patent application no. JP2020-149544, filed on Sep. 7, 2020, the entire contents of which are herein incorporated by reference. 
    
    
     BACKGROUND 
     The present application relates to a battery pack, an electronic device, and an electric tool. 
     Various structures for connecting a battery and a circuit board have been proposed. For example, a structure is described where a circuit board is provided with a through hole, a battery is disposed in the through hole, and the circuit board and the battery are connected with a tab interposed therebetween. 
     SUMMARY 
     The present application relates to a battery pack, an electronic device, and an electric tool. 
     Because the structure described in the Background section is a structure that has a circuit board provided with a through-hole, available batteries are limited to coin-type batteries. In addition, the mounting area of the circuit board is significantly reduced. 
     Accordingly, the present application provides a battery pack that has a configuration capable of appropriately connecting a battery that is larger in size than a coin-type battery and a circuit board, and an electronic device and an electric tool with the battery pack used according to an embodiment. 
     In an embodiment, the present application provides a battery pack including: an exterior case; a circuit board; a battery including a metal exterior can; and a metal member electrically connecting the battery and the circuit board, where an electrode part is provided on at least one end side of the battery, the circuit board and the electrode part are disposed to face each other, the metal member includes a board connection connected to the circuit board, an electrode connection connected to the electrode part, and a side part, the board connection is disposed to face the electrode connection with the side part interposed therebetween, and the board connection, the side part, and the electrode connection are integrally formed. 
     According to t an embodiment, the battery and the circuit board can be appropriately connected. It is to be noted that the contents of the present application are not to be construed as being limited by the effects illustrated in this specification. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    is a diagram referred to in the description of problems to be considered in an embodiment. 
         FIG.  2    is an exploded perspective view of the battery pack according to an embodiment. 
         FIG.  3    is a perspective view of a battery unit of a battery pack according to an embodiment. 
         FIG.  4    includes view A-C; where view A is a front view and a side view of a circuit board according to an embodiment; where view B is additionally a perspective view, a front view, and a side view of a bus bar according to an embodiment; and where view C is additionally perspective views of bus bars connected to a circuit board according to an embodiment respectively as viewed from one side and the opposite side of the circuit board. 
         FIG.  5    is an enlarged view of a part illustrating a circuit board and batteries connected by bus bars according to an embodiment. 
         FIG.  6    includes views A to D which are diagrams for illustrating a modification example of a bus bar. 
         FIG.  7    includes views A to C which are diagrams for illustrating a modification example of a bus bar. 
         FIG.  8    includes views A to C which are diagrams for illustrating a modification example of a bus bar. 
         FIG.  9    includes views A to C which are diagrams for illustrating a modification example of a bus bar. 
         FIG.  10    is a diagram for illustrating a modification example of a bus bar. 
         FIG.  11    is a diagram for illustrating a modification example of a bus bar. 
         FIG.  12    includes views A to C which are diagrams for illustrating a modification example of a bus bar. 
         FIG.  13    is a diagram for illustrating a modification example of a bus bar. 
         FIG.  14    is a diagram for illustrating a modification example of a bus bar. 
         FIG.  15    includes views A to C which are diagrams for illustrating a modification example of a bus bar. 
         FIG.  16    is a diagram for illustrating a modification example of a bus bar. 
         FIG.  17    is a diagram for illustrating a modification example of a bus bar. 
         FIG.  18    is a diagram for illustrating an application example. 
         FIG.  19    is a diagram for illustrating an application example. 
         FIG.  20    is a diagram for illustrating an application example. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, one or more embodiments will be described in further detail including with reference to the drawings. Preferred specific examples of the present application are described below, the contents of which are not to be considered limiting to the present application. It is to be noted that the members recited in the claims are not to be considered specified as members according to an embodiment. In particular, the scope of the present application is, unless otherwise described, not intended to be limited to only the dimensions, materials, and shapes of the constituent members described in the embodiments, the relative configurations thereof, and the description of directions such as upward, downward, leftward, and rightward directions, which are considered by way of illustrative example only. It is to be noted that sizes, positional relationships, and the like of the members illustrated in the respective drawings may be exaggerated for the clarity of description, and for preventing complicated illustrations, only some of reference numerals may be illustrated, or a part of the illustration may be simplified. Furthermore, in the following description, the same names and reference numerals represent the identical or same members, and redundant descriptions thereof will be appropriately omitted. Furthermore, for each element constituting the present application, an aspect may be employed such that one member also serves as multiple elements made of the same member, or conversely, the function of one member can be shared and achieved by a plurality of members. 
     First, for facilitating understanding of the present application according to an embodiment, problems to be considered will be described.  FIG.  1    is a perspective view for illustrating a configuration example of a common battery pack (battery pack  1 ). The battery pack  1  includes two batteries  2 A and  2 B. A circuit board  3  is connected to the batteries  2 A and  2 B. For the battery pack  1 , the back surface of the circuit board  3  are provided with welded parts  4 A and  4 B. The welded part  4 A and the electrode part of the battery  2 A are connected by a metallic plate-shaped member  5 A. In addition, the welded part  4 B and the electrode part of the battery  2 B are connected by a metallic plate-shaped member  5 B. After the connection, the metallic plate-shaped members  5 A and  5 B are bent. 
     The above-described configuration requires a step of bending the metallic plate-shaped members  5 A and  5 B, and generates stress on the bent part of each metallic plate-shaped member. For this reason, as the process becomes complicated, there is a possibility that the bent part of each metallic plate-shaped member will be broken or cracked. In addition, for avoiding the contact between a mounted component on the circuit board  3  and the batteries  2 A and  2 B, it is necessary to dispose an insulating paper  6  between the circuit board  3  and the batteries  2 A and  2 B. In addition, a holder for holding the circuit board  3  or holding a space between the circuit board  3  and the batteries  2 A and  2 B is required. 
     Accordingly, a structure that applies no load to a metal member is desired without bending the metal member connecting the circuit board and the battery. In addition, an insulating member such as an insulating paper is preferably not provided from the viewpoint of allowing for reducing the manufacturing cost and simplifying the manufacturing process. In addition, the metal member preferably has a shape capable of achieving appropriate strength. An embodiment will be described in further detail in view of the foregoing respects. 
     A whole configuration example of a battery pack (battery pack  100 ) according to an embodiment will be described with reference to  FIGS.  2  and  3   .  FIG.  2    is an exploded perspective view of the battery pack  100 , and  FIG.  3    is a perspective view of a battery unit of the battery pack  100 . 
     As shown in  FIG.  2   , the battery pack  100  has a case  11  as an exterior case. The case  11  is formed from, for example, a resin. The case  11  includes a box-shaped lower case  11 A with an upper surface opened and a lid-shaped upper case  11 B that has a rectangular shape in top view. The case  11  has a battery unit  20  housed therein. The lower case  11 A has a predetermined side surface with rectangular holes  12  formed. For example, four holes  12  are formed. Terminal parts provided on a circuit board described later are exposed from the holes  12 . 
     The battery unit  20  includes a battery  21 A, a battery  21 B, a circuit board  22 , a bus bar  23 A and a bus bar  23 B, which are examples of metal members, an insulating paper  24 , a ring-shaped insulating paper  25 , and a relay connection member  26 . 
     The batteries  21 A and  21 B are, for example, lithium ion batteries. The battery  21 A and the battery  21 B are, for example, batteries including electrode parts (positive electrode or negative electrode) at both end surfaces and including cylindrical metal exterior cans. According to the present embodiment, the batteries  21 A and  21 B are arranged so as to differ in polarity at adjacent ends. 
     The circuit board  22  is a board on which an IC (Integrated Circuit) or the like that performs charge/discharge control and protection control for the batteries  21 A and  21 B is mounted. Examples of the protection control include a protection function for preventing overcharge and overdischarge. The circuit board  22  has a predetermined circuit pattern and four terminal parts  221  formed, and the circuit pattern is connected to an appropriate terminal part. According to the present embodiment, the circuit board  22  has a rectangular shape, but may have another shape. 
     The bus bar  23 A is a member that connects the circuit board  22  and a negative electrode terminal provided on one end side of the battery  21 A. In addition, the bus bar  23 B is a member that connects the circuit board  22  and a positive electrode terminal provided on one end side of the battery  21 B. The bus bars  23 A and  23 B are made of a metal member in an appropriate shape. 
     The insulating paper  24  is a member disposed between the batteries for the purpose of insulation between the batteries  21 A and  21 B. In addition, the ring-shaped insulating paper  25  is a member disposed for the purpose of insulation between the positive and negative electrodes of the battery  21 A and protection against migration. 
     The relay connection member  26  is a metallic member that connects the positive electrode terminal of the battery  21 A and the negative electrode terminal of the battery  21 B. The two batteries  21 A and  21 B are connected in series by the relay connection member  26 . In addition, the relay connection member  26  includes a thin plate-shaped relay member  26 A. The relay member  26 A has an end connected to the circuit board  22 . As illustrated in  FIG.  3   , the connection site of the relay member  26 A at the circuit board  22  is connected to a protection IC, and the protection IC is configured to be capable of checking the voltages of the batteries  21 A and  21 B. 
     Next, exemplary shapes of the circuit board  22  and bus bars  23 A and  23 B will be described in detail with reference to  FIGS.  4  and  5   .  FIG.  4 A  is a front view and a side view of the circuit board  22 .  FIG.  4 B  is a perspective view, a front view, and a side view of the bus bar  23 A.  FIG.  4 C  is perspective views of the bus bars  23 A and  23 B connected to the circuit board  22  respectively as viewed from one side and the opposite side of the circuit board  22 .  FIG.  5    is an enlarged view of a part illustrating the circuit board  22  and batteries  21 A and  21 B connected by the bus bars  23 A and  23 B. 
     As illustrated in  FIG.  4 A , the circuit board  22  has two rectangular holes  222 A and  222 B formed on the right side and left side near the center. In addition, the circuit board  22  has a notch  223  formed near the center of the upper side of the circuit board  22  in the longitudinal direction. 
     The circuit board  22  has one main surface  22 A and a main surface  22 B on the side opposite to the main surface  22 A. The main surface  22 A is provided with the above-described terminal parts  221  (terminal parts  221 A to  221 D). In addition, the main surface  22 A is provided with a terminal part  224 . The vicinity of the tip of the relay member  26 A of the relay connection member  26  led through the notch  223  is connected to the terminal part  224 . 
     Next, a configuration example of the bus bar  23 A will be described with reference to  FIG.  4 B . It is to be noted that although the bus bar  23 A will be described herein, the bus bar  23 B has the same configuration as the bus bar  23 A. 
     The bus bar  23 A has a substantially quadrangular prism shape as a whole. Specifically, the bus bar  23 A has a frame-shaped flange  231  on one end side. The flange  231  is an example of a board connection connected to the circuit board  22 . As illustrated in  FIG.  4 C , for example, the flange  231  is solder-joined by reflow to the vicinity of the edge of the hole  222 A in the main surface  22 B of the circuit board  22 . 
     In addition, a protrusion  232  in a quadrangular prism shape is formed from the vicinity of the inner peripheral edge of the flange  231 . The protrusion  232  has a rectangular sectional shape (sectional shape in the case of cutting the protrusion  232  along a plane that is substantially parallel to the extending direction of the flange  231 ). It is to be noted that the rectangular shape means a rectangular shape or a substantially rectangular shape. For example, if a corner is chamfered, the chamfered corner is as one corner. The protrusion  232  has four side parts corresponding to side surfaces and an end surface. According to an embodiment, side-part plates are disposed on all of the side parts, and an end-surface plate is disposed on the end surface. The side-part plates and the end-surface plate are, for example, metallic plate-shaped members. The end-surface plate disposed on the end surface of the protrusion  232  functions as an electrode connection  233 . The flange  231  described above is extended perpendicularly from the side parts of the protrusion  232 , and is disposed to face the electrode connection  233  with the side parts of the protrusion  232  interposed therebetween. In addition, the side parts of the protrusion  232  are erected substantially perpendicular to the electrode connection  233  from the peripheral edge (inner peripheral edge) of the flange  231 . The electrode connection  233  is connected to a negative electrode terminal  211 A of battery  21 A by welding such as resistance welding or laser welding. According to an embodiment, the part between the flange  231  of the bus bar  23 A and the electrode connection  233  has a quadrangular prism shape. In addition, for the bus bar  23 A, the flange  231 , the side parts of the protrusion  232 , and the electrode connection  233  are integrally formed. 
     The electrode connection  233  has a slit formed. For example, the electrode connection  233  has a slit  233 A formed to have an H-shape. The flange  231  of the bus bar  23 B is solder-joined to the main surface  22 B of the circuit board  22 . In addition, the electrode connection of bus bar  23 B is welded to a positive electrode terminal  211 B of the battery  21 B. 
     As illustrated in  FIG.  5   , the circuit board  22  is opposed to face and the negative electrode terminal  211 A of the battery  21 A and the positive electrode terminal  211 B of the battery  21 B. The circuit board  22  and the negative electrode terminal  211 A are connected by the bus bar  23 A. The circuit board  22  and the positive electrode terminal  211 B are connected by the bus bar  23 B. 
     The battery pack  100  described above has, for example, the following operational effects. 
     The circuit board  22  and the batteries  21 A and  21 B are connected by the bus bars  23 A and  23 B in the protruded shapes, thereby allowing a space to be provided between the circuit board  22  and the electrode parts of the batteries  21 A and  21 B, and allowing both to be prevented from coming into contact with each other. Accordingly, the need to use any insulating component is eliminated, thus allowing for reducing the number of components and allowing for reducing the manufacturing cost. 
     In addition, the protrusions of the bus bars  23 A and  23 B have a quadrangular prism shape. Thus, the bus bars  23 A and  23 B can be adjusted to have at least certain strength. Accordingly, at the time of impact due to dropping, the bus bars  23 A and  23 B serve as supports, thereby allowing the circuit board  22  and the electrode parts of the batteries  21 A and  21 B to be prevented from coming into contact with each other. 
     Furthermore, the electrode connections of the bus bars  23 A and  23 B are provided with the slits  233 A. Thus, the electrode connections can be elastically deformed. The electrode connections are elastically deformed, thereby causing the electrode connections to follow the shape of the electrode part. Thus, the adhesion between the electrode connections and the electrode parts of the batteries can be enhanced, and the generation of defective welding at the time of welding can be reduced as much as possible. In addition, the electrode connections are elastically deformed, thereby allowing the absorption of the phase shift and dimensional error between the plurality of batteries, and allowing the generation of defective welding caused by the shift and the error to be avoided as much as possible. Furthermore, the electrode connections are elastically deformed, thereby allowing the flanges to be prevented from being detached from the circuit board due to a dropping impact. 
     Next, modification examples of the metal member will be described. The modification examples of the metal member, described below, can be applied to the above-described bus bars  23 A and  23 B. It is to be noted that the identical or same members or configurations to or as the members or the configurations described in accordance with an embodiment are denoted by the same reference numerals, and redundant descriptions thereof will be appropriately omitted. 
     A first modification example of the metal member will be described with reference to  FIGS.  6 A to  6 D .  FIG.  6 A  is a side view of a bus bar (bus bar  31 ) according to the first modification example,  FIG.  6 B  is a perspective view of the bus bar  31 ,  FIG.  6 C  is a front view of the bus bar  31 , and  FIG.  6 D  is a side view of the bus bar  31  viewed from a direction that is different from that in  FIG.  6 A . 
     As illustrated in  FIG.  6 A , the bus bar  31  has a substantially quadrangular prism shape as with the bus bar  23 A. The bus bar  31  has a flange  311  that functions as a board connection, and has a protrusion  312  protruding from the flange  311 . The protrusion  312  has a quadrangular prism shape and has side parts  312 A and  312 B in the longitudinal direction and side parts  312 C and  312 D in the lateral direction, and a side-part plate is disposed on each side part. In addition, the protrusion  312  has an end surface, and an end-surface plate disposed on the end surface functions as the electrode connection  313 . The flange  311  is disposed to face the electrode connection  313  with the side parts  312 A to  312 D interposed therebetween. In addition, the flange  311 , the side parts  312 A to  312 D, and the electrode connection  313  are integrally formed. 
     The electrode connection  313  has a slit  314  formed therein. As illustrated in  FIG.  6 C , the slit  314  is, for example, a slit extending in the longitudinal direction of the electrode connection  313 . In addition, the slit  314  according to the present modification example is extended from the electrode connection  313  to the side-part plates disposed on the side parts. As illustrated in  FIGS.  6 B and  6 D , for example, the slit  314  is formed across the side-part plates disposed on the side part  312 C and the side part  312 D. As described above, the slit may be extended to at least parts of the side-part plates disposed on the side parts. The slit is extended to the side parts, thereby making the electrode connection more likely to be elastically deformed. 
     Next, a second modification example will be described with reference to  FIGS.  7 A to  7 C .  FIG.  7 A  is a front view and a side view of a circuit board (circuit board  32 ) according to the present modification example.  FIG.  7 B  is a diagram illustrating a configuration example of a bus bar (bus bar  33 ) according to the present modification example.  FIG.  7 C  is a diagram illustrating two bus bars  33  attached to the circuit board  32 . 
     As illustrated in  FIG.  7 A , the circuit board  32  differs from the circuit board  22  in that the circuit board  32  has notches  35 A and  35 B without having the holes  222 A and  222 B. The notches  35 A and  35 B are formed respectively, for example, at the sides of the circuit board  32  in the lateral direction thereof. 
     The bus bars  33  differ from the bus bars  23 A and  23 B mainly in the shape of the flange and the shape of the protrusion. The bus bar  33  has a flange  331  formed in a C-shape. In addition, the bus bar  33  has a protrusion  332  protruded upward from the inner peripheral edge of the flange  331 . The protrusion  332  has a configuration where side-part plates are disposed at the sites of three side parts among the four side parts of the protrusion  232  described in accordance with an embodiment, and has a sectional shape in a C-shape. In addition, the protrusion  332  has an electrode connection  333  that is an end-surface plate disposed on an end surface integrally connected to the three side parts. As illustrated in  FIG.  7 B , the electrode connection  333  has a slit  333 A formed to extend in substantially the same direction as the longitudinal direction of the electrode connection  333 . As illustrated in  FIG.  7 C , the flanges  331  of the two bus bars  33  are soldered by reflow to the respective peripheral edges of the notches  35 A and  35 B. The bus bars described above can also achieve the same operational effects as those of an embodiment. 
     Further, as illustrated in  FIG.  8 B , the flange  331  of the protrusion  332  may have a configuration to form an L-shape. In this case, the protrusion  332  has a configuration where side-part plates are disposed at the sites of two adjacent side parts among the four side parts of the protrusion  232  described in accordance with an embodiment, and has a sectional shape in an L-shape. When the shape of the bus bar  33  is the shape shown in  FIG.  8 B , notches  36 A and  36 B are formed, for example, near the right and upper corners of the circuit board  32  as illustrated in  FIG.  8 A . Then, as illustrated in  FIG.  8 C , the flange  331  of the bus bars  33  are soldered by reflow to the vicinities of the peripheral edges of notches  36 A and  36 B. 
     It is to be noted that the bus bar, specifically, the protrusion preferably has an n-gonal prism shape (n = 4 in the present modification example), with prism shape is n. side-part plates disposed at sites corresponding to n/2 or more side parts, where the number of side parts of the n-gonal. In the case of a shape with side-part plates disposed at sites corresponding to less than n/2 side parts (for example, a shape with a side-part plate disposed on only one side part), the bus bar may be possibly bent by an impact due to welding or dropping. The shape with side-part plates disposed at sites corresponding to n/2 or more side parts, however, is employed, thereby making it possible to maintain a strength capable of preventing the bus bar from being bent against a load applied to the bus bar at the time of welding to the electrode part or at the time of a dropping impact. 
     In addition, as illustrated in  FIGS.  7 B and  8 B , in the case of the configuration with side-part plates disposed at sites corresponding to n/2 or more side parts, the side-part plates are preferably disposed at least on the adjacent side parts. The side-part plates are disposed on the adjacent side parts, thereby allowing the force applied in one direction to be distributed, and allowing the bus bar to be prevented from bending and then falling at the time of welding or an impact applied. 
     Next, a third modification example will be described with reference to  FIGS.  9 A to  9 C .  FIG.  9 A  is a front view and a side view of a circuit board (circuit board  42 ) according to the present modification example.  FIG.  9 B  is a diagram illustrating a configuration example of a bus bar (bus bar  43 ) according to the present modification example.  FIG.  9 C  is a diagram illustrating two bus bars  43  attached to the circuit board  42 . 
     As illustrated in  FIG.  9 A , the circuit board  42  has hexagonal holes  422 A and  422 B on the right side and left side near the center. Terminal parts  221  and  224  are provided on one main surface  42 A of the circuit board  42 . 
     As illustrated in  FIG.  9 B , the bus bar  43  has a hexagonal flange  431 . In addition, the bus bar  43  has a protrusion  432  in a hexagonal prism shape protruded with respect to the flange  431  and protruding from the inner peripheral edge of the flange  431 . The protrusion  432  has six side parts, and in this example, side-part plates are disposed on all of the six side parts. The protrusion  432  has an electrode connection  433  that is an end-surface plate disposed on an end surface, and the electrode connection  433  has a slit  433 A formed therein. The sectional shape of the protrusion  432  forms a hexagonal shape. In addition, the part between the flange  431  of the bus bar  43  and the electrode connection  433  has a hexagonal prism shape. 
     As illustrated in  FIG.  9 C , the bus bar  43  is solder-joined by reflow to the peripheral edge of the hole  422 A in the other main surface  42 B of the circuit board  42 . In addition, the other bus bar  43  is solder-joined by reflow to the peripheral edge of the hole  422 B in the other main surface  42 B of the circuit board  42 . 
     It is to be noted that although it is not necessary to dispose the side-part plates on all of the six side parts of the protrusion  432 , the protrusion  432  preferably, as described above, has an n-gonal prism shape (n = 6 in the present modification example), with side-part plates disposed at sites corresponding to n/2 or more, that is, 3 or more side parts, where the number of side parts of the n-gonal prism shape is n. For example, as illustrated in  FIG.  10   , side-part plates are disposed on three side parts  432 A,  432 B, and  432 C of the protrusion  432 . In addition, as another example, as illustrated in  FIG.  11   , side-part plates are disposed on three side parts  432 B,  432 C, and  432 D of the protrusion  432 . 
     Furthermore, as described above, as a configuration, side-part plates are preferably disposed at least on adjacent side parts. As illustrated in  FIG.  10   , all of the three side parts  432 A,  432 B, and  432 C may be adjacent, or as illustrated in  FIG.  11   , some side parts ( 432 B,  432 C) of the three side parts  432 B,  432 C, and  432 D may be adjacent. In addition, the examples illustrated in  FIGS.  10  and  11    are examples in which side-part plates are disposed on the three side parts, but side-part plates may be disposed on four side parts, or side-part plates may be disposed on five side parts. 
     Next, a fourth modification example will be described with reference to  FIGS.  12 A to  12 C .  FIG.  12 A  is a front view and a side view of a circuit board (circuit board  52 ) according to the present modification example.  FIG.  12 B  is a diagram illustrating a configuration example of a bus bar (bus bar  53 ) according to the present modification example.  FIG.  12 C  is a diagram illustrating two bus bars  53  attached to the circuit board  52 . 
     As illustrated in  FIG.  12 A , the circuit board  52  has circular holes  522 A and  522 B on the right side and left side near the center. Terminal parts  221  and  224  are provided on one main surface  52 A of the circuit board  52 . 
     As illustrated in  FIG.  12 B , the bus bar  53  has a substantially cylindrical shape as a whole. Specifically, the bus bar  53  has a circular flange  531 . In addition, the bus bar  53  has a cylindrical protrusion  532  protruded with respect to the flange  531  and protruding from the inner peripheral edge of the flange  531 . The protrusion  532  has a side part that serves as the side surface of the cylindrical shape, and in this example, a side-part plate is disposed over the whole side part. As described above, in the present modification example, the part between the flange  531  and the electrode connection  533  has a cylindrical shape. The protrusion  532  has the electrode connection  533  that is an end-surface plate disposed on an end surface, and the electrode connection  533  has a slit  533 A formed therein. 
     As illustrated in  FIG.  12 C , the bus bar  53  is solder-joined by reflow to the peripheral edge of the hole  522 A in the other main surface  52 B of the circuit board  52 . In addition, the other bus bar  53  is solder-joined by reflow to the peripheral edge of the hole  522 B in the other main surface  52 B of the circuit board  52 . 
     Further, although it is not necessary to dispose the side-part plate over the whole side part of the protrusion  532 , the side-part plate is preferably disposed at a site corresponding to 1/2 or more of the total area of the side part. Thus, it is possible to maintain a strength capable of preventing the bus bar from being bent against a load applied to the bus bar at the time of welding to the electrode part or at the time of a dropping impact. For example, as illustrated in  FIG.  13   , a side-part plate  532 A is disposed on a half of the side part of the protrusion  532 . It is to be noted that as long as the side-part plate is disposed at a site corresponding to 1/2 or more of the total area of the side part, there is no need for a single side-part plate like the side-part plate  532 A illustrated in  FIG.  13   , and divided side-part plates like the side-part plates  532 B and  532 C may be employed as illustrated in  FIG.  14   . In this case, for distributing the load applied to the bus bar  53  in a well-balanced manner, the side-part plates  532 B and  532 C are preferably disposed at positions substantially facing each other. 
     Next, a fifth modification example will be described with reference to  FIGS.  15 A to  15 C .  FIG.  15 A  is a front view and a side view of a circuit board (circuit board  62 ) according to the present modification example.  FIG.  15 B  is a diagram illustrating a configuration example of a bus bar (bus bar  63 ) according to the present modification example.  FIG.  15 C  is a diagram illustrating two bus bars  63  attached to the circuit board  62 . 
     As illustrated in  FIG.  15 A , the circuit board  62  has elliptical holes  622 A and  622 B on the right side and left side near the center. Terminal parts  221  and  224  are provided on one main surface  62 A of the circuit board  62 . 
     As illustrated in  FIG.  15 B , the bus bar  63  has a substantially elliptic cylindrical shape as a whole. Specifically, the bus bar  63  has an elliptical flange  631 . In addition, the bus bar  63  has a protrusion  632  in an elliptic cylindrical shape protruded with respect to the flange  631  and protruding from the inner peripheral edge of the flange  631 . The protrusion  632  has a side part that serves as the side surface of the elliptic cylindrical shape, and in this example, a side-part plate is disposed over the whole side part. The protrusion  632  has an electrode connection  633  that is an end-surface plate disposed on an end surface, and the electrode connection  633  has an H-shaped slit  633 A formed therein. 
     As illustrated in  FIG.  15 C , the bus bar  63  is solder-joined by reflow to the peripheral edge of the hole  622 A in the other main surface  62 B of the circuit board  62 . In addition, the other bus bar  63  is solder-joined by reflow to the peripheral edge of the hole  622 B in the other main surface  62 B of the circuit board  62 . 
     Further, although it is not necessary to dispose the side-part plate over the whole side part of the protrusion  632 , the side-part plate is preferably disposed at a site corresponding to 1/2 or more of the total area of the side part. Thus, it is possible to maintain a strength capable of preventing the whole side-part plate from being bent against a load applied to the side-part plate at the time of welding to the electrode part or at the time of a dropping impact. For example, as illustrated in  FIG.  16   , a side-part plate  632 A is disposed on a half of the side part of the protrusion  632 . It is to be noted that in the case of such a configuration, the area for supporting the electrode connection  633  is reduced. Thus, for increase the bending strength of the electrode connection  633  (the strength against a force applied in a direction orthogonal to the main surface of the electrode connection  633 ), the area of the slit  633 A may be reduced. For example, as illustrated in  FIG.  16   , the shape of the slit  633 A may be changed from the H-shape to an elliptical shape. 
     It is to be noted that as long as the side-part plate is disposed at a site corresponding to 1/2 or more of the total area of the side part, there is no need for a single side-part plate like the side-part plate  632 A illustrated in  FIG.  16   , and divided side-part plates like the side-part plates  632 B and  632 C may be employed as illustrated in  FIG.  17   . In this case, for distributing the load applied to the bus bar  63  in a well-balanced manner, the side-part plates  632 B and  632 C are preferably disposed at positions substantially facing each other. 
     While an embodiment of the present application has been described above, the contents of the present application are not to be considered limited thereto, and it is possible to make various modifications based on technical idea of the present application. 
     The metal exterior can of the battery may have the cylindrical shape described in an embodiment, or may have another shape, for example, an angular shape. In the case of the angular shape, the positive electrode terminal and the negative electrode terminal may be led out from the same end. More specifically, the positive electrode terminal and the negative electrode terminal may be provided at different ends as in the embodiment, or may be provided on the same end side. 
     The configurations of the circuit board, bus bar, and battery unit can be appropriately changed without departing from the scope of the present application. For example, the battery unit may have three or more batteries, and three or more bus bars may be used so as to correspond to the three or more batteries. 
     The matters described in the above-described embodiments and modification examples can be appropriately combined. In addition, the materials, processes, and the like described in the embodiments are considered merely by way of example, and the contents of the present application are not to be considered limited to the exemplified materials or the like. 
     The battery pack according to the present application can be used for mounting on various electronic devices such as a wireless phone, an electric tool, an electric vehicle, or the like, or for supplying electric power thereto. 
     Next, a specific application example will be described. For example, the above-described battery pack can be used as a power supply for a wearable device that has the function of a portable information terminal, that is, a so-called wearable terminal. Examples of the wearable terminal include, but not to be considered limited thereto, a wristwatch-type terminal and a glasses-type terminal. 
       FIG.  18    shows an example of a wearable terminal that has a built-in a battery pack. As illustrated in  FIG.  18   , the wearable terminal  730  according to the application example is a wristwatch-type terminal, which includes therein a battery pack  732 . The battery pack according to the present application can be applied as the battery pack  732 . The wearable terminal  730  can be worn and then used by the user. The wearable terminal  730  may be a deformable flexible terminal. 
     As illustrated in  FIG.  19   , the wearable terminal  730  according to the application example includes an electronic circuit  731  of an electronic device main body, and the battery pack  732 . The battery pack  732  is electrically connected to the electronic circuit  731 . The wearable terminal  730  has, for example, a configuration that allows the user to attach/detach the battery pack  732 . It is to be noted that the configuration of the wearable terminal  730  is not limited thereto, and the battery pack  732  may be configured to be built in the wearable terminal  730  so that the user is not allowed to remove the battery pack  732  from the wearable terminal  730 . 
     In the case of charging the battery pack  732 , the positive electrode terminal  734 A and negative electrode terminal  734 B of the battery pack  732  are respectively connected to a positive electrode terminal and a negative electrode terminal of a charger (not shown). In contrast, in the case of discharging the battery pack  732  (in the case of using the wearable terminal  730 ), the positive electrode terminal  734 A and negative electrode terminal  734 B of the battery pack  732  are respectively connected to a positive electrode terminal and a negative electrode terminal of the electronic circuit  731 . 
     The electronic circuit  731  includes, for example, a CPU, a peripheral logic unit, an interface unit, a storage unit, and the like, and controls the wearable terminal  730 . 
     The battery pack  732  includes the battery pack according to an embodiment and a charge/discharge circuit  733  . 
     Next, an application example to which the battery pack according to the present application can be applied will be described. First, an example of an electric driver as an electric tool to which the present application can be applied will be schematically described with reference to  FIG.  20   . An electric driver  831  is provided with a motor  833  that transmits rotative power to a shaft  834  and a trigger switch  832  operated by a user. A battery pack  830  according to the present application and a motor control unit  835  are housed in a lower housing of a handle of the electric driver  831 . The battery pack  830  is built in the electric driver, or detachable from the electric driver  831 . 
     The battery pack  830  and the motor control unit  835  each may include a microcomputer (not shown), such that charge/discharge information of the battery pack  830  can be communicated with each other. The motor control unit  835  can control the operation of the motor  833 , and cut off the power supply to the motor  833  at the time of abnormality such as overdischarge. 
     DESCRIPTION OF REFERENCE SYMBOLS 
     
       
         
           
               
               
            
               
                   11 : 
                 Exterior case 
               
               
                   22 : 
                 Circuit board 
               
               
                   21 A,  21 B: 
                 Battery 
               
               
                   23 A,  23 B: 
                 Bus bar 
               
               
                   100 : 
                 Battery pack 
               
               
                   211 A: 
                 Negative electrode terminal 
               
               
                   211 B: 
                 Positive electrode terminal 
               
               
                   231 : 
                 Flange 
               
               
                   232 : 
                 Protrusion 
               
               
                   233 : 
                 Electrode connection 
               
               
                   233 A: 
                 Slit 
               
            
           
         
       
     
     It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.