Abstract:
A method comprising: assembling a battery pack core; holding the core in a mold that forms a molded resin region; closing a cavity of the mold; injecting synthetic resin into the closed cavity; and ejecting the battery pack from the cavity to configure the battery pack with the battery pack core insert-molded in the molded resin region. A projection that protrudes towards an inner surface of the mold cavity is provided on the surface of the insulating cover fixed on the battery. In the resin injection step, the projection on the insulating cover is pressed directly or indirectly by the mold in a direction putting the insulating cover tightly in contact with the surface of the battery; and synthetic resin is injected into the cavity of the mold in this pressed configuration.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a battery pack and method of manufacture wherein a battery pack core is insert molded into a molded resin region. Specifically, this invention relates to a battery pack and method of manufacture that temporarily holds a battery pack core in a mold that forms the molded resin region, and attaches the molded resin region to the battery in a process step that forms the molded resin region. 
         [0003]    2. Description of the Related Art 
         [0004]    A prior art battery pack is assembled by inserting a battery pack core, which is an assembly of parts essential to the battery, into a plastic external case. Since a battery pack of this configuration is assembled while inserting and fastening the battery pack core into a fixed position in the external case, its manufacture is difficult. In contrast, a battery pack that does not use an external case has been developed. This type of battery pack is manufactured by insertion of a battery pack core when a molded resin region is formed. The molded resin region is equivalent to the external case. A battery pack with this configuration is manufactured by connecting parts essential to the battery as a battery pack core, temporarily holding the battery pack core in the mold cavity that forms the molded resin region, injecting molten synthetic resin into the mold cavity, and as a result, inserting the battery pack core into the injected synthetic resin. Since the battery can be fixed in place in the battery pack during molded resin region formation, the external case can be omitted and the battery pack can be efficiently manufactured in quantity. The molded resin region not only forms part of the external case of the battery pack, it also serves to solidly attach various parts connected to the battery into a single unit. Consequently, since the battery pack core can be fixed in place when the molded resin region is formed, the battery pack has the characteristic that it can be efficiently and inexpensively manufactured in quantity. 
         [0005]    In a battery pack of this configuration, the exhaust outlet of the safety valve provided on the battery is closed off by the molded resin region. Gas discharged from an open safety valve escapes to the outside through gaps formed between the battery and the molded resin region. Accordingly, gaps are generated between the battery and the molded resin region attached to the battery during molding by pressure from gas discharged from the safety valve. In this type of battery pack, when the battery pack core is temporarily held in the mold cavity and molten synthetic resin is injected into the mold cavity, the molten synthetic resin can destroy the safety valve. To prevent this detrimental effect, a battery pack has been developed that forms the molded resin region with the exhaust outlet of the safety valve covered by an insulating cover (refer to Japanese Patent Laid-Open Publication No. 2004-213931). 
       SUMMARY OF THE INVENTION 
       [0006]    In the battery pack cited in the Publication 2004-213931, the molded resin region is insert molded with an insulating cover closing off the exhaust outlet of the safety valve. However, even though the battery pack is formed by insert molding the battery in the molded resin region with the insulating cover closing off the exhaust outlet of the safety valve, the safety valve can still be damaged by the molded resin region. This is because insulating cover position can shift during molded resin region formation and it becomes impossible to reliably close off the safety valve exhaust outlet. In addition, the twisting strength of a battery pack with this structure can degrade due to shift in the position of the insulating cover during molded resin region formation. Twisting strength degradation with shift in insulating cover position is because the insulating cover cannot be inserted in the proper position inside the molded resin region. 
         [0007]    The present invention was developed to further resolve these drawbacks. Thus, it is an important object of the present invention to provide a battery pack and method of manufacture that reliably prevents shift in insulating cover position during molded resin region formation and reliably prevents destruction of the safety valve by the molded resin region, and in addition prevents twisting strength degradation by accurately inserting the insulating cover in proper position. 
         [0008]    The method of manufacture of the present invention has an assembly step to assemble a battery pack core  10  by layering an insulating cover  4 ,  54  that covers the exhaust outlet  13  of the safety valve  12  on the battery  2 ; a holding step to hold the battery pack core  10  in the mold  30  that forms the molded resin region  1 ; a resin injection step to close the cavity  31  of the mold  30  that holds the battery pack core  10  and inject synthetic resin into the closed cavity  31  of the mold  30 ; and a mold ejection step to remove the battery pack from the cavity  31  of the mold  30  with the battery pack core  10  insert molded in the molded resin region  1 . Further, a projection  15  that protrudes towards an inner surface of the cavity  31  of the mold  30 , which forms the molded resin region  1 , is provided on the surface of the insulating cover  4 ,  54  layered on the battery  2 . In the resin injection processing step of the method of manufacture, the projection  15  on the insulating cover  4 ,  54  is pressed directly or indirectly by the mold  30  in a direction putting the insulating cover  4 ,  54  tightly in contact with the surface of the battery  2 , and synthetic resin is injected into the cavity  31  of the mold  30  in this pressed configuration. 
         [0009]    The present invention prevents shift in the position of the insulating cover during molded resin region formation, and reliably prevents destruction of the safety valve by the molded resin region. It also inserts the insulating cover in an precise position in the molded resin region to achieve the characteristic that degradation in twisting strength can be prevented. This is because a projection that protrudes towards an inner surface of the mold cavity, which forms the molded resin region, is provided on the surface of the insulating cover layered on the battery. The battery pack is fabricated by injecting synthetic resin into the mold cavity with the projection pressed upon by the mold to tightly secure the insulating cover on the surface of the battery. In the battery pack core secured in the mold cavity, the insulating cover is retained in a fixed position by pressure from the mold on the insulating cover projection. With the projection of the insulating cover pressed by the mold, the insulating cover tightly contacts the surface of the battery secured in the mold. The assembly is retained in this configuration while molten synthetic resin is injected into the mold cavity. Therefore, synthetic resin injected into the mold cavity does not shift the position of the insulating cover. In particular, the insulating cover does not become separated from the surface of the battery and molten synthetic resin does not ingress between the insulating cover and the battery. As a result, synthetic resin does not ingress between the insulating cover and the battery, does not ingress into the safety valve exhaust outlet, and does not damage the safety valve. 
         [0010]    Since the insulating cover projection is pressed upon by the mold when the battery pack core is secured in the mold cavity, the position of the insulating cover is not shifted by the injected synthetic resin. Therefore, the insulating cover is inserted in a precise position in the molded resin region formed in the mold cavity. A structure that insert molds the insulating cover in a precise position in the molded resin region can improve twisting strength of the fabricated unit. The reason for this is understood by assuming an insulating cover is insert molded in a shifted position in the molded resin region and part of the insulating cover is either exposed outside the molded resin region or is extremely close to the surface of the molded resin region. In this situation, the insulating cover will deform to move away from the battery if a twisting force is applied to the battery pack having a locally thinned molded resin region. 
         [0011]    In the battery pack core  10  assembly step of the method of manufacture of the present invention, a lead plate  5  can be disposed on the projection  15  of the insulating cover  4 ,  54  to make a battery pack core  10  that is provided with an insulating cover  4 ,  54  and lead plates  5 . A metal plate provided with an alignment slit  16 A for inserting the projection  15  of the insulating cover  4 ,  54  is used as the lead plate  5 . The battery pack core  10  is assembled with the insulating cover  4 ,  54  projection  15  inserted through the alignment slit  16 A of the lead plate  5 . In this method, the lead plate  5 , which is aligned by the insulating cover  4 ,  54  disposed in a fixed position, can also be disposed in a fixed position. Consequently, both the insulating cover  4 ,  54  and the lead plate  5  can be insert molded in a precise positions in the molded resin region  1 . 
         [0012]    Further, in the battery pack core  10  assembly step of the method of manufacture of the present invention, a circuit board  3  can be disposed on the projection  15  of the insulating cover  4 ,  54 . In the resin injection process step, synthetic resin can be injected into the mold cavity  31  with the mold  30  pressing the insulating cover  4 ,  54  into close contact with the battery  2  surface via the intervening circuit board  3 . This method can form the molded resin region  1  with the battery pack core  10  secured in the mold cavity  31  and both the insulating cover  4 ,  54  and the circuit board  3  retained in precise positions. This is because both the insulating cover  4 ,  54  and the circuit board  3  are pressed upon by the mold  30  to avoid any shift in position. Consequently, in a battery pack manufactured by this method, both the insulating cover  4 ,  54  and the circuit board  3  can be insert molded in a precise positions in the molded resin region  1 . 
         [0013]    Further, in the battery pack core  10  assembly step of the method of manufacture of the present invention, a circuit board with a test point established on its surface can be used as the circuit board  3  disposed on the insulating cover  4 ,  54 . The circuit board  3  can be provided with an externally exposed region  3 A on its front side opposite a pressure region  3 B on its backside. The pressure region  3 B presses against the projection  15  of the insulating cover  4 ,  54 , and a test point  18  is provided on the externally exposed region  3 A. In the resin injection-process step, the externally exposed region  3 A of the circuit board  3  is pressed by a securing pin  32  in the mold  30 . The securing pin  32  presses the externally exposed region  3 A of the circuit board  3  and the pressure region  3 B of the circuit board  3  in turn presses the projection  15  of the insulating cover  4 ,  54 . This secures the circuit board  3  and the insulating cover  4 ,  54  in fixed positions in the mold cavity  31  for molded resin region  1  formation. Here, a test window  19  that opens the externally exposed region  3 A to the outside can be formed in the molded resin region  1  by the securing pin  32 . In this method, the molded resin region  1  is formed with the battery pack core  10  secured in the mold cavity  31 , and the circuit board  3  and the insulating cover  4 ,  54  held in fixed positions by the securing pin  32 . As a result, the circuit board  3  and insulating cover  4 ,  54  can be insert molded in fixed positions in the molded resin region  1 , and a test window  19  to expose the test point  18  to the outside is formed by the securing pin  32  that retains the circuit board  3  and the insulating cover  4 ,  54  in those fixed positions. Consequently, while insert molding the insulating cover  4 ,  54  and the circuit board  3  in precise positions, the test window  19  to externally expose the test point  18  can be formed simultaneously. 
         [0014]    The battery pack of the present invention is provided with a battery  2  having a safety valve  12 , an insulating cover  4 ,  54  disposed in a position opposite the exhaust outlet  13  of the safety valve  12  of the battery  2 , and a molded resin region  1  attached to the battery  2  while inserting the insulating cover  4 ,  54 . The insulating cover  4 ,  54  is provided with a projection  15  on its surface that is pressed in a direction towards the surface of the battery  2  by the mold  30 , which forms the molded resin region  1 . In this battery pack, with the projection  15  pressed by the mold  30  and the battery pack core  10  secured in the mold  30 , the insulating cover  4 ,  54  can be retained in a precise position. As a result, the insulating cover  4 ,  54  can be inserted in a precise position in the molded resin region  1  formed under these conditions. 
         [0015]    The battery pack of the present invention can be provided with a lead plate  5  disposed on the insulating cover  4 ,  54 . The lead plate  5  is provided with an alignment slit  16 A to insert the projection  15  of the insulating cover  4 ,  54 . The battery pack can have a configuration that disposes the lead plate  5  on the insulating cover  4 ,  54  with the projection  15  inserted in the alignment slit  16 A. In a battery pack with this configuration, both the insulating cover  4 ,  54  and the lead plate  5  can be inserted in precise positions in the molded resin region  1 . 
         [0016]    The battery pack of the present invention can be configured with a circuit board  3  disposed on the projection  15  of the insulating cover  4 ,  54 . In this battery pack configuration, the insulating cover  4 ,  54  can be retained in a fixed position by pressure from the mold  30  via the circuit board  3 . Consequently, both the insulating cover  4 ,  54  and the circuit board  3  can be insert molded in precise positions in the molded resin region  1 . 
         [0017]    Further, the battery pack of the present invention can be configured with a circuit board  3  provided with a test point  18  on an externally exposed region  3 A of the front surface, which is exposed outside the molded resin region  1 . The backside of the externally exposed region  3 A of the circuit board  3  can be established as a pressure region  3 B that presses the projection  15  of the insulating cover  4 ,  54 . The battery pack can be configured with a test window  19  provided in the molded resin region  1  to expose the test point  18  to the outside at the externally exposed region  3 A of the circuit board  3 . In this battery pack configuration, the externally exposed region  3 A of the circuit board  30  can be pressed by the mold  30  that forms the test window  19 , and the projection  15  of the insulating cover  4 ,  54  can in turn be pressed by the pressure region  3 B provided on the backside of the externally exposed region  3 A allowing the assembly to be secured in a fixed position. With this configuration, the mold  30  that provides the test window  19  in the molded resin region  1  can dispose both the circuit board  3  and the insulating cover  4 ,  54  in fixed positions. Consequently, the circuit board  3  and the insulating cover  4 ,  54  can be inserted in precise positions in the molded resin region  1 , and this can be done with the mold  30  that forms a test window  19  in the molded resin region  1  to expose the test point  18  to the outside. 
         [0018]    Further, the battery pack of the present invention can have an insulating cover  4 ,  54  that is a molded plastic piece. 
         [0019]    Still further, the battery pack can be configured with a exhaust outlet  13  of the safety valve  12  provided in the sealing cap  11  of the battery  2 , and a protruding ridge  14  established around the perimeter of the sealing cap  11 . The battery pack can be configured to pressure fit the insulating cover  4 ,  54  inside the protruding ridge  14 . With this structure, the insulating cover  4 ,  54  can be inserted in the molded resin region  1  in an even more precise position. 
         [0020]    Finally, since the insulating cover  4 ,  54  of the battery pack of the present invention is adhered to the battery  2 , the molded resin region  1  can be formed with the insulating cover  4 ,  54  pressed by the mold  30  to secure it in a fixed position while additionally it is adhered to the battery  2 . Therefore, the insulating cover  4 ,  54  of this battery pack can be inserted in an extremely precise position in the molded resin region  1 . 
         [0021]    The above and further objects of the present invention as well as the features thereof will become more apparent from the following detailed description to be made in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is an oblique view of a battery pack for an embodiment of the present invention; 
           [0023]      FIG. 2  is an exploded oblique view of the battery pack of  FIG. 1 ; 
           [0024]      FIG. 3  is an exploded oblique view showing the connecting structure of the battery and insulating cover of the battery pack shown in  FIG. 2 ; 
           [0025]      FIG. 4  is a cross-section view showing formation of the molded resin region of a battery pack for an embodiment of the present invention; and 
           [0026]      FIG. 5  is an exploded oblique view showing the connecting structure of the battery and insulating cover of a battery pack for another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    The battery pack shown in  FIGS. 1-4  is manufactured by insert molding a battery pack core  10  in a molded resin region  1 .  FIG. 2  is an exploded oblique view of the battery pack.  FIG. 2  shows the molded resin region  1 , the circuit board  3 , the lead plates  5 , the insulating cover  4  and the battery  2  separately to easily understand each part. In the fabrication process that forms the molded resin region  1 , the circuit board  3 , lead plates  5 , and insulating cover  4  are insert molded in the molded resin region  1  of the battery pack. Therefore, in the molded state with the molded resin region  1  formed, the molded resin region  1  adheres to the battery pack core  10 . Although one part of the battery pack core  10  of the figures is inserted in the molded resin region  1 , the present invention does not limit the part of the battery pack core that is inserted in the molded resin region to the insulating cover, the lead plates, and the circuit board. This is because, although not illustrated, the entire battery pack core can also be inserted in the molded resin region. A battery pack that inserts one part of the battery pack core  10  in the molded resin region  1  can be made compact overall. A battery pack that inserts the entire battery pack core in the molded resin region can improve overall durability. 
         [0028]    The battery pack of the figures has a battery  2  provided with a exhaust outlet  13  of the safety valve  12  in the sealing cap  11 , which is the end plane of the battery provided with a protruding electrode  2 B. Therefore, the molded resin region  1  is formed to cover the end plane of the battery that is the sealing cap  11 . However, in the battery pack of the present invention, a safety valve exhaust outlet can be provided in the end plane opposite the sealing cap, and molded resin region can be attached there. Further, although not illustrated, safety valve exhaust outlets can be provided on both side surfaces of a battery, and molded resin region can also be established to cover those safety valve opening surfaces. 
         [0029]    As shown in  FIG. 4 , the battery pack is manufactured by holding the battery pack core  10  inside the cavity  31  of the mold  30 , and injecting molten synthetic resin into the mold cavity  31  to insert mold one part of the battery pack core  10  in the molded resin region  1 . 
         [0030]    The battery pack core  10  is made up of a battery  2 , an insulating cover  4  that is disposed in a position opposite the exhaust outlet  13  of the safety valve  12  established on the battery  2  and that also serves to insulate the lead plate  5  from the battery  2 , a lead plate  5  disposed on the insulating cover  4 , and a circuit board  3  disposed on the lead plates  5  and connected to the lead plates  5 . 
         [0031]    The battery  2  is a lithium ion battery. However, the battery can be any rechargeable battery such as a nickel hydride battery or nickel cadmium battery instead of a lithium ion battery. In the battery pack of the figures, the battery is a thin outline battery. A thin outline battery is shaped with curved surfaces on both sides and the four corner regions of the external case have rounded edges. If a lithium ion battery is used as the thin outline battery, charge capacity can be increased for a given battery pack volume. As shown in  FIGS. 2 and 3 , this battery  2  is provided with a safety valve  12  on the sealing cap  11 , which has the protruding electrode  2 B. This battery  2  is provided with a protruding electrode  2 B in the center region of the sealing cap  11  and is provided with a safety valve  12  at one end. The safety valve  12  opens when internal battery  2  pressure exceeds a set pressure. In the safety valve  12  of the figures, the exhaust outlet  13  is covered by a thin membrane that breaks if internal pressure exceeds the set pressure. The thin membrane safety valve  12  has a simple structure, but the insulating cover  4  can deform under the pressure of molded resin region  1  formation and break the membrane. In the battery pack of the present invention, a stiff insulating cover  4  is disposed to cover the exhaust outlet  13  of the safety valve  12 , and destruction of the safety valve  12  by synthetic resin pressure in forming the molded resin region  1  is prevented. However, in the battery pack of the present invention, any configuration of safety valve that will open when a set pressure is reached can also be used. For example, a safety valve with a flexible piece that elastically presses a valve piece can also be used. If synthetic resin ingresses into the exhaust outlet of this type of safety valve as well, the valve piece will be opened and it will not operate properly. A properly operating safety valve will open when internal battery pressure exceeds a set pressure allowing internal gas, etc. to escape and stopping the rise in internal pressure. 
         [0032]    The insulating cover  4  is disposed opposite the exhaust outlet  13  of the safety valve  12  of the battery  2  on the sealing cap  11 , which is the surface provided with the safety valve  12  opening. The insulating cover  4  is shaped with an outline that follows the perimeter of the battery  2  end plane and is formed to fit on one side of that end plane. However, as shown in  FIG. 5 , the insulating cover can also be shaped with an outline that can be pressure fit inside a protruding ridge  14  provided around the perimeter of the sealing cap  11 , and that can fit inside the protruding electrode  2 B and the protruding ridge  14 . This insulating cover  54  can be pressure fit inside the protruding ridge  14  and disposed in a precise position on the sealing cap  11 . 
         [0033]    The insulating cover  4  closes off the exhaust outlet  13  of the safety valve  12  during formation of the molded resin region  1 , and it is disposed between the lead plate  5  and the sealing cap  11  to insulate the lead plate  5  from the sealing cap  11 . The insulating cover  4  is hard insulating plate that does not deform under the pressure of synthetic resin injection to form the molded resin region  1  with the battery pack core  10  secured in the mold cavity  31 . For example, the insulating cover can be a hard synthetic resin plate such as a fiber-glass reinforced epoxy plate, or a phenol plate. However, in the present invention, the insulating cover is not limited to a hard synthetic resin plate and can be any hard plate material that is insulating or has an insulating surface. For example, a metal plate with surfaces covered by an insulating layer, or inorganic material processed in a plate form can also be used. 
         [0034]    As shown in  FIG. 4 , the insulating cover  4  is provided with a projection  15  on its surface that is pressed upon by a securing pin  32  in the mold  30  that forms the molded resin region  1 . This projection  15  extends in a direction towards an inner surface of the mold cavity  31 , and is pressed upon by a securing pin  32  provided in the cavity  31  of the mold  30 . When the molded resin region  1  is formed, the projection  15  is pressed upon by the securing pin  32  in the closed mold  30  to press the insulating cover  4  into tight contact with the surface of the battery  2 . In the battery pack of the figures, a circuit board  3  is disposed on the end surface of the insulating cover  4  projection  15 . In this battery pack configuration, when molten synthetic resin is injected into the mold cavity  31 , the insulating cover  4  projection  15  is pressed by the mold  30  securing pin  32  via the circuit board  3  to urge the insulating cover  4  in a direction to tightly contact the battery  2  surface. The front side of the circuit board  3  of the figures is provided with a test point  18  in an externally exposed region  3 A, which is exposed outside the molded resin region  1 . On the backside of the externally exposed region  3 A of the circuit board  3 , a pressure region is established that presses against the projection  15  on the insulating cover  4 . In this configuration of battery pack, the securing pin  32  of the mold  30  presses against the externally exposed region  3 A of the circuit board  3 , and the pressure region  3 B provided on the backside of the externally exposed region  3 A presses against the projection  15  on the insulating cover  4  causing tight connection of the insulating cover  4  to the surface of the battery  2 . In particular, this battery pack can dispose both the circuit board  3  and the insulating cover  4  in fixed positions with a mold  30  that establishes a test window  19  in the molded resin region  1  to expose the test point  18  at the externally exposed region  3 A of the circuit board  3 . 
         [0035]    The insulating cover  4  shown in  FIGS. 2-4  is provided with a projection  15  that is positioned opposite the exhaust outlet  13  of the safety valve  12 . However, the insulating cover projection can also be displaced laterally from the safety valve exhaust outlet and provided in a position that presses against the surface of the sealing cap. 
         [0036]    The projection  15  has a lateral cross-sectional shape that is narrow and long in the direction of the long side of the sealing cap  11 . This projection  15  presses the insulating cover  4  against the battery  2  sealing cap  11  over a given length and puts the insulating cover  4  in tight contact with the sealing cap  11  over a long area. In addition, a long narrow projection  15  is optimal for insertion through the alignment slit  16 A of the lead plate  5 . This is because the through-hole  16  provided in the lead plate  5  can be made as a narrow alignment slit  16 A. A through-hole  16  provided in the lead plate  5  for inserting the projection  15  increases lead plate  5  electrical resistance and reduces lead plate  5  strength. By making the through-hole  16  as a narrow alignment slit  16 A, lead plate  5  resistance increase and strength loss can be reduced, and the lead plate  5  and insulating cover  4  can be connected without position shift. 
         [0037]    The insulating cover  4  is fixed to the battery  2  sealing cap  11  via double-sided adhesive tape  6 . The double-sided adhesive tape  6  preferably has sufficient thickness to absorb uneven topology in the attachment region. This double-sided adhesive tape  6  can reliably and tightly adhere the insulating cover  4  to the sealing cap  11 , which is the surface the of battery  2 , and also serves to protect the safety valve  12 . When the safety valve  12  opens, the double-sided adhesive tape  6  delaminates and gas escapes to the outside. In a battery pack with the insulating cover  4  adhered to the battery  2 , the double-sided adhesive tape  6  prevents shift in the position of the insulating cover  4  until the battery pack core  10  is secure in the mold  30  and the molded resin region  1  has been formed. Double-sided adhesive tape  6  allows simple attachment of the insulating cover  4  to the battery  2  surface. Further, double-sided adhesive tape  6  delaminates quickly with an open safety valve  12 , and gas can quickly escape from the open safety valve  12 . The insulating cover  4  can also be attached to the battery surface via an adhesive or bond. In the same manner as double-sided adhesive tape, adhesives and bonds are used that have bonding strength allowing them to delaminate with gas pressure from an open safety valve. 
         [0038]    In the battery pack of the figures, one end of the lead plate  5 A is connected to the protruding electrode  2 B of the battery  2 . The other end of this lead plate  5 A is connected to the circuit board  3 . Further, in the battery pack of the figures, a lead plate  5 B is also connected to the sealing cap  11  of the battery  2  and the other end of this lead plate  5 B also connects to the circuit board  3 . The circuit board  3  thereby connects to positive and negative electrodes of the battery  2  via the pair of lead plates  5 , which is made up of the lead plate  5 A connected to the protruding electrode  2 B and the lead plate  5 B connected to the sealing cap  11 . The pair of lead plates  5  are fabricated by cutting sheet metal in the form of a strip of given width. The pair of lead plates  5  joins the circuit board  3  to the battery  2  in a fixed position. In the battery pack of the figures, the pair of lead plates  5  connects to both ends of the circuit board  3 . In a battery pack of this configuration, the circuit board  3  can be joined stably in a fixed position to the battery  2  via the pair of lead plates  5 . 
         [0039]    The lead plate  5 A connected to the protruding electrode  2 B is disposed on the insulating cover  4 . The insulating cover  4  insulates the lead plate  5 A connected to the protruding electrode  2 B and prevents it from touching the sealing cap  11 . This lead plate  5 A is provided with a through-hole  16  for inserting the projection  15  provided on the insulating cover  4 . Since the lateral cross-sectional shape of the projection  15  is long and narrow, the through-hole  16  is made as a long, narrow alignment slit  16 A. The projection  15  on the insulating cover  4  fits through the alignment slit  16 A through-hole  16  to dispose the lead plate  5 A on the Insulating cover  4  in a fixed position that will not shift. Further, the projection  15  that passes through the through-hole  16  of the lead plate  5 A is pressed by a securing pin  32  in the mold  30  without intervention of the lead plate  5 A. Since a circuit board  3  is disposed on the projection  15  in the battery pack of the figures, the insulating cover  4  is pressed by the securing pin  32  via the circuit board  3 . The pair of lead plates  5  is connected to the protruding electrode  2 B and the sealing cap  11  of the battery  2  by spot welding or laser welding. The lead plates  5  are connected to the circuit board  3  by soldering. The lead plates  5  are provided with connecting pieces  5   a  that are bent at right angles at the ends of the lead plates  5  and connect with the circuit board  3 . The circuit board  3  is provided with through-holes  17  to accept the connecting pieces  5   a . The connecting pieces  5   a  are passed through the through-holes  17  and soldered to connect them to the circuit board  3 . In addition, an insulating sheet  7  is disposed between the circuit board  3  and the pair of lead plates  5  connected to the circuit board  3 . This insulating sheet  7  prevents the lead plates  5  from touching the circuit board  3 . 
         [0040]    Protection devices  8  that protect the battery  2  while charging and discharging are mounted on the surface of the circuit board  3 , and a connector  9  that becomes the output terminals of the battery pack is fixed to the circuit board  3 . The protection devices  8  are elements such as PTC devices or fuses. Protection circuitry (not illustrated) that detects battery  2  voltage and controls charging and discharging is also mounted on the circuit board  3 . If voltage of a discharging battery drops below a minimum voltage or voltage of a charging battery becomes greater than a maximum voltage, the protection circuitry cuts off the discharging or charging current. 
         [0041]    A plurality of flexible contacts  22  that become output terminals are housed in the connector case  20  of the connector  9  attached to the circuit board  3 . The connector case  20  is formed from insulating plastic in a shape that mates with an electrical equipment plug (not illustrated). The connector case  20  of the figures is provided with three recessed regions  21  that accept the electrical equipment plug and connect in a pressure fit manner. Disposed inside each recessed region  21  is a flexible contact  22  made of flexible sheet metal, and a metal contact on the inserted plug makes electrical contact with that flexible contact  22 . The connector  9  is attached to the circuit board  3  and the flexible contacts  22  are electrically connected to the circuit board  3 . The circuit board  3  with the connector  9  attached is insert molded and disposed in a fixed position in the molded resin region  1 . 
         [0042]    A layer of primer (not illustrated) can be applied to surfaces of the battery pack core  10  that attach to the molded resin region  1  to strongly adhere the battery pack core  10  and the molded resin region  1 . However, a primer layer is not always required for the battery pack core, which can be insert molded and fixed in the molded resin region without applying primer. In the fabrication process that forms the molded resin region  1 , a battery pack core  10  with primer applied is strongly adhered to the molded resin region  1 . In particular, a primer layer strongly adheres the molded resin region  1  to metal surfaces of the battery  2 . Primer applied to the circuit board  3 , and to the connector  9  and protection devices  8  attached to the surface of the circuit board  3  firmly adheres them to the molded resin region  1 . A primer layer is applied to surfaces that attach to the molded resin region  1 . The primer layer is a liquid primer solution in the unhardened state and can be sprayed, applied with a brush, or the battery pack core  10  can be dipped in the primer solution. The primer layer can be provided on necessary parts of the battery pack core  10  as a unit, or it can be applied to battery  2  surfaces, the circuit board  3 , protection devices  8 , and the connector  9  before assembling the battery pack core  10 . Primer layer provided on the surface of the connector  9  is applied to regions excluding electrical contacts such as the flexible contacts  22 . This is because primer layer can be a cause of poor electrical contact. Since the primer layer as adequate effect as a thin layer, layer thickness is made ˜1 μm. However, primer layer thickness can also be made from 0.5 μm to 5 μm. Since the primer layer serves to protect battery surfaces as well as strengthening adhesion of the molded resin region  1 , layer thickness can be increased to improve its protective properties. 
         [0043]    The molded resin region  1  of the battery pack can be formed from polyamide resin, and the primer layer can be an epoxy resin type primer. In the polyamide molded resin region  1 , epoxy radicals in the primer layer introduced into acid amide bonds in the resin chemically bond in the primer layer. Therefore, the molded resin region  1  is strongly adhered to the primer layer. Instead of, or in addition to epoxy resin primer, other primers such as denatured epoxy resin type primer, phenol resin type primer, denatured phenol resin type primer, polyvinyl butyl resin type primer, and polyvinyl formal resin type primer can also be used. A plurality of these primers mixed together can also be used. These types of primers chemically bond with the polyamide molded resin region  1 , and they form hydrogen bonds or chemically bond with metal surfaces to strongly adhere the molded resin region  1  to battery surfaces. 
         [0044]    Synthetic resin used to form the molded resin region  1  is polyamide resin. Epoxy resin can also be added to the polyamide resin. Compared with polyamide resin only, polyamide resin with epoxy resin added has stronger adhesion. Since polyamide resin becomes pliable at a low temperature and has low viscosity in the molten state, it can be molded at lower temperature and pressure than other thermoplastic synthetic resins. Further, it has the characteristic that it can be quickly ejected from the mold cavity. A molded resin region  1  that is formed at low temperature and pressure has the characteristic that molding time can be reduced, and the detrimental effects of heat and injection pressure during molding on elements such as the protection devices  8  can be reduced. However, in the battery pack of the present invention, the resin for forming the molded resin region  1  is not limited to polyamide resin. Resins other than polyamide, such as polyurethane can also be used. Further, if the ability of the protection devices  8  to withstand high temperature is improved, other thermoplastic resins such as polyethylene, acrylic, and polypropylene can also be used. 
         [0045]    The molded resin region  1  is provided with a thin band  1   a  established around the perimeter of the sealing cap  11  and extending to the surface of the external case  11  of the battery  2 . The thin band  1   a  is formed as a single piece with the molded resin region  1 , and is attached to the surface of the perimeter of the battery  2  when the molded resin region  1  is formed. As shown in  FIG. 4 , molten resin injected into the cavity  31  of the mold  30  injects from around the perimeter of the sealing cap  11  into the region that forms the thin band  1   a . This forms the molded resin region  1  and thin band  1   a  as a single piece. The thin band  1   a  is preferably formed around the entire perimeter of the sealing cap  11 . This molded resin region  1 , which has a thin band  1   a  provided around the entire perimeter of the sealing cap  11 , is joined to the battery in a fashion most unlikely to delaminate. However, the thin band can also be provided along one part of the battery perimeter. For example, the thin band  1   a  can be provided only along the wide surfaces of a thin outline battery. 
         [0046]    The width of the thin band  1   a  can be increased to increase battery  2  attachment strength. Even if the thin band  1   a  is made relatively narrow, the molded resin region  1  can be strongly adhered to the battery  2 . In particular, in a battery pack with a covering sheet (not illustrated) attached to the metal surfaces of the battery  2 , the covering sheet can press the thin band  1   a  against the battery surfaces in a manner that keeps it from delaminating. Consequently, the thin band  1   a  can be made narrow and still securely attach the molded resin region  1  to the battery  2 . The width of the thin band  1   a  can be 0.1 mm to 2 mm, preferably 0.2 mm to 1 mm, and for example, can be 0.5 mm. With a narrow thin band  1   a , molten synthetic resin can be reliably injected into the thin band  1   a  region of the mold  30  and the specified shape can be molded. 
         [0047]    The covering sheet is heat shrink tubing that contracts with heat. This covering sheet is tightly attached to the surface of the thin band  1   a  of the molded resin region  1  to securely join the molded resin region  1  to the battery  2 . Further, in a battery pack covered by a covering sheet, things that are a source of delamination cannot ingress between the thin band  1   a  and the battery  2 . In this respect as well, the covering sheet can prevent the thin band  1   a  from delaminating from the battery  2 . Labeling and adhesive tape can also be used as a covering sheet. For a covering sheet that is labeling or adhesive tape, it attaches from the molded resin region and surface of the thin band to the battery surface, and securely joins the molded resin region to the battery. 
         [0048]    As shown in  FIG. 1 , a step  24  is established around the perimeter of the molded resin region  1  of the battery pack, and the covering sheet can cover the thinly formed region of the step  24 . In this molded resin region  1 , the covering sheet does not protrude out from the molded resin region  1 , and the surface of the molded resin region  1  and the surface of the covering sheet can be in approximately the same plane. 
         [0049]    In the battery pack of  FIG. 1 , a molded plastic piece  23 , which is formed separately from the molded resin region  1  is attached to the opposite end from the sealing cap  11 , which has the molded resin region  1  attached. Specifically, the molded plastic piece  23  is attached to the bottom surface of the external case  2 A of the battery  2 . The molded plastic piece  23  is formed from plastic that is harder than the molded resin region  1 . This molded plastic piece  23  is formed as a single piece with a bottom  23 A that covers the entire bottom surface of the external case  2 A and a second thin band  23   a  that extends from the bottom surface of the external case  2 A to the outer surfaces of the battery  2 . The bottom  23 A is formed thicker than the second thin band  23   a.    
         [0050]    The battery pack described above is manufactured by the following steps. 
       (1) Battery Pack Core  10  Assembly Step 
       [0051]    In this step, the insulating cover  4  is disposed on the sealing cap  11  of the battery  2  in a manner that covers the exhaust outlet  13  of the safety valve  12  provided on the sealing cap  11  of the battery  2 . In the battery pack core  10  of the figures, the lead plate  5 A, which is connected to the protruding electrode  2 B by spot welding, is disposed on the insulating cover  4 . This lead plate  5 A is joined to the circuit board  3  by soldering. The projection  15  on the insulating cover  4  is passed through the through-hole  16  in the lead plate  5 A to connect the lead plate  5 A on the insulating cover  4  in a fixed position. Another lead plate  5 B is connected to the sealing cap  11  of the battery  2  by spot welding, and the other end of this lead plate  5 B is connected to the circuit board  3 . The lead plates  5  and circuit board  3  are joined to the battery  2  to make the battery pack core  10 . Protection devices  8  and a connector  9  are connected on the circuit board  3 . A primer layer can be provided to parts of the battery pack core  10  where the molded resin region  1  attaches to increase attachment strength of the molded resin region  1 . However, since it is not always necessary to provide a primer layer, the primer layer application step can also be omitted. 
       (2) Holding Step 
       [0052]    The assembled battery pack core  10  is mounted and secured in the cavity  31  of the mold  30  that forms the molded resin region  1 . Here, the battery pack core  10  is secured in the mold cavity  31  in a manner that will avoid any shift in position. Specifically, to retain the battery pack core  10  mounted in the mold cavity  31  in a fixed position, the entire outer surface of the battery  2  is sandwiched to maintain its position. In addition, the circuit board  3  is retained in a fixed position via retaining pins (not illustrated) that extend from the mold  30  into the mold cavity  31 . Further, the securing pin  32  provided in the mold  30  presses the projection  15  on the insulating cover  4  towards the surface of the battery  2  via the intervening circuit board  3 . This presses the insulating cover  4  against the surface of the battery  2 . In the battery pack of  FIG. 4 , the perimeter edge of the insulating cover  4  is pressed against the end of the protruding ridge  14  provided around the perimeter of the battery  2 . In the battery pack of  FIG. 5 , the insulating cover  54 , which is pressure fit inside the protruding ridge  14 , is pressed against the surface of the sealing cap  11 . In this manner, the insulating cover  4 ,  54 , with its projection  15  pressed upon by the securing pin  32 , is tightly attached to the surface of the battery  2 . This arrangement is maintained through the next step, which is the resin injection step. Consequently, even in the next resin injection step, the insulating cover  4  is retained in tight contact with the surface of the battery  2 . 
       (3) Resin Injection Step 
       [0053]    The mold  30  is closed and sealed with the battery pack core  10  secured in the mold cavity  31 , and molten synthetic resin is injected into the mold cavity  31 . Synthetic resin injected into the mold cavity  31  forms the molded resin region  1 . The molded resin region  1  formed in the mold cavity  31  has the circuit board  3 , lead plates  5 , and insulating cover  4  inserted. The molded resin region  1  exposes part of the connector  9 , which is mounted on the circuit board  3 , to the outside. In addition, the thin band  1   a  attached around the perimeter of the battery  2  is also formed. Further, one part of the molded plastic piece can also be inserted in the molded resin region. 
       (4) Mold Ejection Step 
       [0054]    After the molten synthetic resin injected into the mold cavity  31  has cooled and hardened, the mold  30  is opened and the battery pack is ejected from the mold  30 . The battery pack ejected from the mold  30  has part of the battery pack core  10  inserted in the molded resin region  1  formed in the mold cavity  31  and the molded resin region  1  is tightly joined to the battery  2 . 
         [0055]    Finally, although not illustrated, the battery pack is inserted in surface covering sheet, which is cylindrical heat shrink tubing. Heat is applied to the heat shrink tubing to tightly attach it to the surface of the battery pack. The surface covering sheet tightly attaches to the surface of the thin band  1   a  of the molded resin region  1  and to the surface of the second thin band  23   a  of the molded plastic piece  23 . This solidly connects the molded resin region  1  and the molded plastic piece  23  to the battery  2 . 
         [0056]    It should be apparent to those with an ordinary skill in the art that while various preferred embodiments of the invention have been shown and described, it is contemplated that the invention is not limited to the particular embodiments disclosed, which are deemed to be merely illustrative of the inventive concepts and should not be interpreted as limiting the scope of the invention, and which are suitable for all modifications and changes falling within the spirit and scope of the invention as defined in the appended claims. The present application is based on Application No. 2006-324649 filed in Japan on Nov. 30, 2006, the content of which is incorporated herein by reference.