Abstract:
The purpose of the present invention is to provide simpler and more reliable electrical wiring than a lead wire. A battery pack includes at least one rechargeable secondary battery ( 1 ), a battery holder ( 70 ) for housing the secondary battery ( 1 ) in a predetermined position, a pack circuit board ( 74 ) having a mounted electronic circuit for monitoring the secondary battery ( 1 ), and an electrical connection wire ( 85 ) for electrically wiring the pack circuit board ( 74 ). Here, the electrical connection wire ( 85 ) is a bent metal wire. Because wiring is realized using metal wire, and the metal connection is secured after the wiring has been completed, movement and deformation due to vibrations and other factors, such as that which occurs in the case of conventional lead wires, are avoided, and reliability can be improved. Because the present invention has the simple configuration of a bent metal wire, manufacturing can be simplified, manufacturing costs can be reduced, and components requiring insulation to improve reliability can be reduced, thereby lowering material costs.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a battery pack detachably installed in a battery-powered device such as a power tool, an electric lawn mower, or an electric blower to supply electric power. 
     BACKGROUND 
     A battery-powered device such as a power tool can be used cordlessly, for example, at a construction site, when a detachable battery pack containing rechargeable batteries is provided. When the remaining capacity of a battery pack is low, the battery pack is placed in a battery pack charger and recharged. 
       FIG. 28  through  FIG. 34  show an example of such a battery pack.  FIG. 28  is an external perspective view of the battery pack,  FIG. 29  is an exploded perspective view of the battery pack in  FIG. 28 ,  FIG. 30  is a perspective view of the battery holder  70 X in  FIG. 29 ,  FIG. 31  is a perspective view of the battery holder in  FIG. 30  with the pack circuit board  74 X removed from the battery holder  70 X,  FIG. 32  is a vertical cross-sectional view of the battery holder  70 X from line XXXII-XXXII in  FIG. 30 ,  FIG. 33  is an enlarged cross-sectional view of  FIG. 32 , and  FIG. 34  is a perspective view of the power lead. The battery pack in these drawings contains a battery holder  70 X in which a plurality of secondary batteries have been connected, and a pack circuit board  74 X on which electronic circuitry for monitoring the batteries has been mounted. Lead wires and battery lead plates  80 X are used to wire the pack circuit board  74 X and the secondary batteries. The end faces of the secondary batteries are connected using battery lead plates  80 X, and lead wires are used to connect the battery lead plates  80 X to the pack circuit board  74 X. A thick-diameter power lead  85 X is used to wire a high-voltage output line. 
     However, the thick power lead  85 X is wired in a tight space, and is not easy to solder. It is difficult to bend the power lead in the confined space as indicated by the solid arrows in  FIG. 33  and  FIG. 34 . Even when the power lead  85 X can be soldered, the power lead  85 X can still move freely after being wired. For example, the lead wire sometimes moves in the direction indicated by the broken line arrow in  FIG. 33 . Therefore, when the battery pack is subjected to vibrations or impacts, the power lead  85 X moves inside the battery pack. The lead wire may be worn down and exposed by friction, become disconnected, or come into contact with a component having a different voltage and short-circuit. 
     To resolve this problem, the wiring of the pack circuit board using metal lead plates has been considered. However, a large amount of space is required to arrange a circuit board using lead plates, and the conductivity is poor because thin plates are used. As battery packs get smaller, there will be increasing demand for reliable wiring in smaller wiring spaces. However, a wiring structure able to meet this demand has not yet been developed. 
     For an example, see Japanese Laid-open Patent Application No. 2010-146879. 
     SUMMARY 
     The present invention has been devised in view of the problem associated with the prior art. The main purpose of the present invention is to provide a battery pack with simpler and more reliable electrical wiring than a lead wire. 
     In order to achieve this purpose, a first aspect of the present invention is a battery pack includes at least one rechargeable secondary battery  1 , a battery holder  70  for housing the secondary battery  1  in a predetermined position, a pack circuit board  74  having a mounted electronic circuit for monitoring the secondary battery  1 , and an electrical connection wire  85  for electrically wiring the pack circuit board  74 . Here, the electrical connection wire  85  is a bent metal wire. Because wiring is realized using metal wire, and the metal connection is secured after the wiring has been completed, movement and deformation due to vibrations and other factors, such as that which occurs in the case of conventional lead wires, are avoided, and reliability can be improved. Because the present invention has the simple configuration of a bent metal wire, manufacturing can be simplified, manufacturing costs can be reduced, and components requiring insulation to improve reliability can be reduced, thereby lowering material costs. 
     A second aspect of the present invention is a battery pack in which the electrical connection wire  85  is an output line of the secondary battery  1 . In this way, a high-voltage output line can be used stably over a long time as a highly reliably electrical connection. 
     A third aspect of the present invention is a battery pack in which the electrical connection wire  85  has a bent portion  85   a  bent into a C-shape. In this way, the bent portion can be used to position the electrical connection properly. For example, twisting of the electrical connection can be prevented during wiring. Also, when the electrical connection is subjected to external shocks, deformation of the bent portion lessens the shock, and damage to the connection portion can be reduced. 
     A fourth aspect of the present invention is a battery pack in which the battery holder  70  has a plurality of holding ribs  78  for holding the bent portion  85   a  of the electrical connection wire  85  on the upper surface of the battery holder. In this way, the electrical connector with a bent portion can be positioned properly in both the length direction and the height direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a battery pack according to a first embodiment; 
         FIG. 2  is a perspective view showing a rear view of the battery pack in  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of the battery pack from the position in  FIG. 1 ; 
         FIG. 4  is an exploded perspective view of the battery pack from the position in  FIG. 2 ; 
         FIG. 5  is an exploded perspective view of the battery holder; 
         FIG. 6  is a perspective view of the battery holder; 
         FIG. 7  is a perspective view of the battery holder in  FIG. 6  with the pack circuit board removed; 
         FIG. 8  is a perspective view of the battery holder in  FIG. 7  with the electrical connection wires removed; 
         FIG. 9  is a perspective view of the battery holder in  FIG. 6  from the left side; 
         FIG. 10  is a top view of the battery holder in  FIG. 9 ; 
         FIG. 11  is a side view of the battery holder in  FIG. 10 ; 
         FIG. 12  is a vertical cross-sectional view of the battery holder from line XII-XII in  FIG. 10 ; 
         FIG. 13  is an external perspective view of an electrical connection wire; 
         FIG. 14  is a side view of a battery holder of the prior art; 
         FIG. 15  is an enlarged view of the main portion of the battery holder in  FIG. 14 ; 
         FIG. 16  is an enlarged view of portion XVI of the battery holder in  FIG. 11 ; 
         FIG. 17  is an enlarged view of portion XVII of the battery holder in  FIG. 10  in which a lead pin has been inserted into a lead hole in the battery lead plate; 
         FIG. 18  is a vertical cross-sectional view of the battery holder from line XVIII-XVIII in  FIG. 10 ; 
         FIG. 19  is an enlarged cross-sectional view of portion XIX in  FIG. 18  showing a guiding rib; 
         FIG. 20  is an enlarged perspective view showing a portion of the battery pack in  FIG. 10  in which a lead pin has been inserted into a lead hole using the guiding rib; 
         FIG. 21  is a vertical cross-sectional view of the battery holder from line XXI-XXI in  FIG. 11 ; 
         FIG. 22  is an enlarged cross-sectional view of portion XXII of the battery holder in  FIG. 21  in which a lead pin has been secured in a pin securing hole; 
         FIG. 23  is a top view showing a battery holder of the prior art; 
         FIG. 24  is an enlarged view of portion XXIV of the battery holder in  FIG. 23  in which a lead pin has been secured in a pin securing hole; 
         FIG. 25  is an exploded perspective view showing the lead pin in  FIG. 24  being secured in a pin securing hole; 
         FIG. 26  is an enlarged view of portion XXVI of the battery holder in  FIG. 10  in which a lead pin has been secured in a pin securing hole; 
         FIG. 27  is an exploded perspective view showing the lead pin in  FIG. 26  being secured in a pin securing hole; 
         FIG. 28  is an external perspective view showing a battery pack of the prior art; 
         FIG. 29  is an exploded perspective view of the battery pack in  FIG. 28 ; 
         FIG. 30  is a perspective view of the battery holder in  FIG. 29 ; 
         FIG. 31  is a perspective view of the battery holder in  FIG. 30  with the pack circuit board removed; 
         FIG. 32  is a vertical cross-sectional view of the battery holder from line XXXII-XXXII in  FIG. 30 ; 
         FIG. 33  is an enlarged cross-sectional view of  FIG. 32 ; and 
         FIG. 34  is a perspective view of the power lead shown in  FIG. 32 . 
     
    
    
     DETAILED DESCRIPTION 
     The following is an explanation of an embodiment of the present invention with reference to the drawings. The embodiment described below is used to illustrate a battery pack realizing the technical concepts of the present invention. The present invention is not specific to the battery pack described below. Also, the components described in the claims are not specific to the components in the embodiment. The dimensions, materials, shapes and relative arrangement of the configurational elements described in the embodiments, unless otherwise indicated, do not limit the scope of the present invention and server merely as an explanatory example. The sizes and relative positions of the components shown in the drawings may be exaggerated for illustrative purposes. In the following explanation, identical or similar components are indicated by the same name and are denoted by the same reference number. A detailed explanation is omitted where appropriate. A plurality of elements constituting the present invention may be combined into a single element, or a plurality of elements may work together as a single element. Conversely, the function of a single element may be divided and realized using a plurality of elements. Also, details described in one embodiment or example may be applied to another embodiment or example. 
     Example 1 
       FIG. 1  through  FIG. 4  show a battery pack for a power tool which is the battery pack in the first embodiment of the present invention.  FIG. 1  is a perspective view showing a battery pack  30 ,  FIG. 2  is a perspective view showing a rear view of the battery pack  30  in  FIG. 1 ,  FIG. 3  is an exploded perspective view of the battery pack  30  from the position in  FIG. 1 , and  FIG. 4  is an exploded perspective view of the battery pack  30  from the position in  FIG. 2 . The following is an explanation of a battery pack for a power tool. However, the battery pack of the present invention is not limited to battery packs for power tools. The present invention can be adapted for use in any other type of battery-powered device. 
     The battery pack  30  in these drawings has a box-like profile and contains secondary batteries  1 . More specifically, the battery pack  30  includes a battery holder  70  for housing a plurality of rechargeable secondary batteries  1 , battery lead plates  80  connected to the secondary batteries  1  on their end faces, a pack circuit board  74  on which a protection circuit for the secondary batteries  1  has been mounted, a plurality of external connection terminals  33  connected to the battery-operated device or battery pack charger, and a battery case  31  housing the battery holder  70  and the pack circuit board  74 . 
     (Battery Case  31 ) 
     As shown in  FIG. 1  and  FIG. 2 , the battery case  31  has a box-like profile with rounded corners. The external connection terminals  33  protrude from the surface to connect the case to the connection terminals of a battery-operated device or battery pack charger. The battery pack  30  has a latching unit  50  for securing the pack when it has been attached to a battery-operated device or battery pack charger. The battery case  31  is molded from a resin with superior insulating properties and strength. 
     As shown in the exploded perspective views of  FIG. 3  through  FIG. 4 , the battery case  31  is divided in half into an upper casing  31 A and a lower casing  31 B. A storage space is configured inside the battery case  31  for housing the battery holder  70 , the pack circuit board  74 , and the latching unit  50 . The sides of the battery case  31  are covered by side covers  31 C. The side covers  31 C are combined as separate components with the upper casing  31 A and the lower casing  31 B. The edges of the side covers  31 C are inserted into grooves provided in the upper casing  31 A and the lower casing  31 B, and are interposed between and secured by the upper casing  31 A and the lower casing  31 B. 
     (Battery Holder  70 ) 
     As shown in  FIG. 3  through  FIG. 5 , the battery holder  70  includes secondary batteries  1 , a pack circuit board  74 , battery lead plates  80 , and different types of lead wires. The battery holder  70  is also provided with a battery storage space for storing secondary batteries  1  on the lower surface, and a circuit board securing portion  75  for securing the pack circuit board  74  on the upper surface. The secondary batteries  1  are connected to the battery lead plates  80  on the end faces of the secondary batteries  1  exposed by the exposed portion  71  in the end face of the battery holder  70 , and the output of the battery core storing the secondary batteries  1  in the battery holder  70  is connected to the pack circuit board  74  via an output lead plate and an output lead wire. The battery lead plates  80  are also connected to the pack circuit board  74  via a signal lead wire  84 . 
     (External Connection Terminals  33 ) 
     The battery pack  30  has a plurality of external connection terminals  33  connected to a battery-operated device or battery pack charger. The external connection terminals  33  are secured to the pack circuit board  74 . In addition to the outputs from the secondary batteries  1 , signal terminals can be provided for exchanging signals with an externally connected battery pack charger or battery-operated device. These external connection terminals  33  are bent metal plates. As shown in  FIG. 6  and  FIG. 9 , each external connection terminal  33  has a rear end bent into a C-shape when viewed from above. The open end of the C-shape is bent in a tapered fashion so as to become gradually narrower at the tip connected electrically to a connection terminal on an externally connected device such as a battery pack charger or battery-operated device. The connection terminal on the externally connected device is inserted between the two bent metal plates, and is interposed between the two metal plates to establish an electrical connection. 
     (Latching Unit  50 ) 
     As shown in  FIG. 1  through  FIG. 4 , the latching unit  50  provided on the battery pack  30  is movably housed inside the battery case  31  and partially exposed inside the battery case  31 . The latching unit  50  has a detachment unit  52  on the front surface which is operated manually by the user, and an engaging hook  54  in the upper portion in the drawing which has both an inclined surface inclined in the forward direction when attached to the battery pack  30 , and a perpendicular surface formed continuously with the perpendicular surface. The engaging hook  54  is integrally molded with the detachment unit  52 . A hook protrusion window  15  is formed in the upper case  31 A from which the engaging hook  54  on the latching unit  50  protrudes. A holding recess  17  is formed in the detachment unit  52  in a position corresponding to the engaging hook  54 . This holding recess  17  also has a recessed inclined surface aligned with the inclined surface of the hook, and a recessed perpendicular surface aligned with the horizontal surface of the hook. 
     (Protection Circuit) 
     A protective circuit for the secondary batteries  1  is mounted on the pack circuit board  74 . The protective circuit is connected via battery lead plates  80  and a signal lead wire to detect the voltage of each secondary battery  1 . The external connection terminals  33  of the pack circuit board  74  include charge/discharge terminals, and signal terminals for outputting signals from the protective circuit and battery information. As shown in  FIG. 2 , these charge/discharge terminals and signal terminals are exposed on the surface of the battery case  31 . 
     (Secondary Batteries  1 ) 
     The battery case  31  is molded into a shape able to store secondary batteries  1 . Here, the secondary batteries  1  are cylindrical storage batteries in which the cylindrical outer canister is arranged in the longitudinal direction. As shown in  FIG. 4 , the battery case  31  includes a plurality of secondary batteries  1  arranged side-by-side on the same plane so as to be parallel to each other inside the battery case  31 . The secondary batteries  1  housed inside the battery pack  30  are lithium-ion batteries. However, the secondary batteries can be any other type of rechargeable battery, including nickel-metal hydride batteries, nickel-cadmium batteries, and polymer batteries. The secondary batteries can be connected in series to increase the output voltage, or connected in parallel to increase the output current. In this example, the secondary batteries  1  are lithium-ion batteries, five pairs of batteries arranged in parallel are connected in series, and the output voltage is 18 V. However, there are no restrictions on the number of secondary batteries or their connection arrangement. The battery pack can be designed freely based on the type of battery-operated device being used, the intended use of the battery-operated device, and the number of secondary batteries and the output voltage being used. 
     (Battery Storage Space) 
     As shown in the exploded perspective view of  FIG. 5 , the battery storage space of the battery holder  70  is divided in half into a first subholder  71 A and a second subholder  71 B, and the secondary batteries  1  are interposed between the first subholder  71 A and the second subholder  71 B. In this example, the battery holder holds ten secondary batteries  1 . In the battery holder  70 , the secondary batteries  1  housed inside the battery storage space are connected by their end surfaces exposed in the exposed portion  71  to the battery lead plates  80 . 
     (Battery Lead Plate  80 ) 
     As shown in the exploded perspective view of  FIG. 5 , the battery lead plates  80  are flat metal plates with superior conductive properties that are formed into a size that can be housed inside the battery storage space. Welding slits are formed in the battery lead plates  80  for spot welding, and are secured to the end surface of adjacent secondary batteries  1  housed inside the battery storage space. 
     (Circuit Board Securing Portion  75 ) 
     A circuit board securing portion  75  is provided in the upper surface of the battery holder  70  to secure the pack circuit board  74 .  FIG. 6  and  FIG. 7  show a pack circuit board  74  mounted in the circuit board securing portion  75 .  FIG. 6  is a perspective view of the battery holder  70 , and  FIG. 7  is a perspective view of the battery holder  70  in  FIG. 6  with the pack circuit board  74  removed. The battery holder  70  shown in these drawings has bosses  72  for supporting the pack circuit board  74 . Boss holes  76  are provided in the pack circuit board  74  in positions corresponding to the bosses  72 . The tip of a boss  72  is inserted into the boss hole  76  from the underside of the pack circuit board  74 , and secured using a screw or some other means. While not shown in the drawings, this example has a column protruding towards the pack circuit board  74  on the inner surface of the upper casing  31 A in each position corresponding to a boss  72 . Each column has an insertion pin on the tip. The insertion pin of each column is passed through a threaded hole in which a screw is inserted, and connected to a threaded hole  37  formed in the upper surface of the upper casing  31 A. As shown in  FIG. 3  and  FIG. 4 , a screw  38  can be screwed into the threaded hole  37  from the upper casing  31 A to secure the pack circuit board  74  to the upper casing  31 A. 
     (Electrical Connection Wire  85 ) 
     This pack circuit board  74  uses electrical connection wires  85  instead of power lead wires to connect the outputs from the secondary batteries  1  housed inside the battery holder  70 . This arrangement is shown in  FIG. 8  through  FIG. 13 .  FIG. 8  is a perspective view of the battery holder  70  in  FIG. 7  with the electrical connection wires  85  removed.  FIG. 9  is a perspective view of the battery holder  70  in  FIG. 6  from the left side.  FIG. 10  is a top view of the battery holder  70  in  FIG. 9 .  FIG. 11  is a side view of the battery holder  70  in  FIG. 10 .  FIG. 12  is a vertical cross-section sectional view of the battery holder  70  from line XII-XII in  FIG. 10 .  FIG. 13  is an external perspective view of an electrical connection wire  85 . The electrical connection wires  85  in these drawings are bent metal wires. Both ends of the metal electrical connection wires  85  are bent as shown in  FIG. 13 . As shown in  FIG. 9 , one end is inserted into the pack circuit board  74 , the other end is inserted into a battery lead plate  80 , and both ends are soldered in place. Both ends can be bent in different directions as shown in  FIG. 13 , and can flexibly conform to the connection route. A connection hole  74   c  is formed in the pack circuit board  74  for inserting an end of an electrical connection wire  85 . The end of the electrical connection wire  85  is inserted into the connection hole  74   c , and secured to the pack circuit board  74  using soldering or some other means. 
     The metal connection wires  85  can be made of a metal with superior electrical conductivity such as nickel, tin or copper. The wire can be round or flat like a lead plate, and suppress both resistivity and joule heat. The metal connection wires do not run along the surface of the pack circuit board  74  like a lead wire or lead plate. Instead, both ends are bent so that the wire floats above the surface of the pack circuit board  74 . Because there is space between the wire and the surface of the pack circuit board  74 , this arrangement is advantageous from the standpoint of insulating properties and heat dissipating properties. Because the wire is not flexible like a lead wire, it does not move on account of mechanical vibrations or impacts. It also does not wear down due to fiction and disconnect. Because the metal connection wire is a simple bent metal wire, manufacturing costs are kept down, and the metal connection wires are easy to machine. Use of bent metal electrical connection wires  85  in this way is superior to conventional lead wires and lead plates from the standpoint of reliability, workability, and machinability. 
     (Holding Ribs  78 ) 
     As shown in the exploded perspective view of  FIG. 8 , the electrical connection wires  85  are secured to the upper surface of the battery holder  70 . As shown in the exploded perspective view of  FIG. 7 , they are also secured to the pack circuit board  74 . A plurality of holding ribs  78  are formed in the upper surface of the battery holder  70  to hold the electrical connection wires  85 . 
     (Bent Portion  85   a ) 
     As shown in the perspective view of  FIG. 13 , the electrical connection wire  85  can be formed with a C-shaped (U-shaped) bent portion  85   a  in the middle. As shown in the exploded perspective view of  FIG. 8 , this bent portion can be held in a predetermined position by holding ribs  78  of different heights. In other words, among the holding ribs  78  provided on the upper surface of the battery holder  70 , the height of the pair of middle holding ribs  78   b  for holding the bent portion  85   a  can be increased in response to the depth of the bent portion  85   a . As a result, positioning of the electrical connection wire  85  is achieved which would be inherently easy to rotate when linear, and the ends can be inserted properly into the pack circuit board  74  and the battery lead plate  80 . In particular, when the end of an electrical connection wire  85  is inserted into a connection hole  74   c  in the pack circuit board  74  during assembly, turning of the metal wire is prevented by the middle holding ribs  78   b . Also, the electrical connection wire  85  can be positioned longitudinally by holding both ends of the C-shaped bent portion  85   a  using a pair of middle holding ribs  78   b . By guiding the electrical connection wire  85  using a plurality of holding ribs, the deformation of the electrical connection wire  85  can also be lessened when subjected to the force of an external impact. 
     The bent portion  85   a  is preferably positioned near the center of the electrical connection wire  85 . In this way, stable positioning can be achieved. When subjected to a strong external impact, a hard metal wire is more likely to transmit the impact than a flexible lead wire, so there is a possibility that the impact force will be transmitted to a connection and cause damage. By providing a bent portion  85   a , the impact force can be absorbed by the deformed bent portion  85   a . This can be expected to reduce the risk of damage to the connection. 
     In this example, the electrical connection wire  85  is an output line from a secondary battery. However, the present invention is not restricted to this example. The bent metal electrical connection wire  85  can also be a signal wire. 
     (Measuring Midpoint Potential) 
     In order to determine the status of each secondary battery  1  in a battery pack  30  in which a plurality of secondary batteries  1  have been connected, the midpoint potential is measured. When the secondary batteries  1  are lithium-ion batteries, the cell voltage of each secondary battery is measured. In this configuration, the voltage is measured at each battery lead plate  80  connected to secondary batteries, and the voltage value is transmitted to the pack circuit board  74 . More specifically, the pack circuit board  74  secured to the upper surface of the battery holder  70  is connected electrically to the battery lead plates  80 , and the protection circuit mounted on the pack circuit board  74  monitors the voltage status. Also, the battery lead plates  80  are secured to the secondary batteries  1  on the side surfaces of the battery holder  70 , and the status of the secondary batteries  1  is monitored by the pack circuit board  74 . A lead plate securing frame  86  is provided on the side surface of the battery lead plates  80  to secure each battery lead plate  80 . 
     (Lead Pin  90 ) 
     The pack circuit board and the battery lead plates are connected via lead pins. This arrangement will now be explained with reference to the side view of the battery holder  70 X shown in  FIG. 14  and the enlarged view in  FIG. 15  of the portion surrounded by the dotted lines in  FIG. 14 . As shown in the drawings, the lead pin  90  is a bent thin metal wire. The lead pin  90  is inserted into a pin securing hole  74   a  in the pack circuit board  74  and secured. The other end of the lead pin  90  engages a battery lead plate  80 X and is secured. The other end of the lead pin  90  is the engaging end  91  which is bent as shown in the enlarged view of  FIG. 15 . A slit  80   a  is provided in the battery lead plate  80 X to engage the engaging end  91  of the lead pin  90 . The slit  80   a  is formed in the far end of the battery lead plate  80 X as viewed from the pack circuit board  74 . When the other end of the lead pin  90  is engaged in the slit  80   a  in this manner, the lead pin  90  has been secured and will not come out. If necessary, the lead pin  90  and the battery lead plate  80 X can be secured using soldering. 
     In this configuration, the tip of the lead pin  90  has to be manually inserted into the slit in the battery lead plate  80 X by the operator. In order to guide the operator in cutting the other end of the lead pin  90  in the slit, the lead pin  90  is pulled once and pushed into the slit. It is then turned up in the opposite direction to secure the pin. In order to realize this engaging operation, as shown in the enlarged view of  FIG. 15 , the space indicated by d has to be provided between the edge of the battery lead plate  80 X including the slit and the lead plate securing frame  86  in the battery holder  70 X. This space is only required during assembly of the battery pack, and remains after assembly. However, narrowing the width of the upper portion of the battery lead plate  80 X to eliminate this inefficient use of space increases processing costs because of the need for a slit with a more complicated shape in the battery lead plate  80 X. It also reduces the strength of the portion in which the lead pin  90  is secured to the battery lead plate  80 X. 
     (Lead Opening  81 ) 
     By contrast, in battery pack  30  of the present embodiment, as shown in  FIG. 11  and  FIG. 16 , a lead opening  81  is formed in the upper end of the battery lead plate  80  for inserting the engaging end  91  of the lead pin  90 . This lead opening  81  is closed off. In other words, because the lead opening  81  does not have a slit leading to the edge of the battery lead plate  80 , the strength of the battery lead plate  80  is increased. Also, as is clear in a comparison of  FIG. 15  and  FIG. 16 , there is no guiding slit as in a battery lead plate  80  of the prior art. As a result, the upper end of the battery lead plate  80  can be increased by an equivalent amount. This increases the mechanical strength of the battery lead plate  80 , and the width of the lead opening can be extended in the length direction of the lead pin  90 . In other words, the width of the lead opening  81  can be increased. This makes the lead engaging end  91  easier to insert into the lead opening  81 , and contributes to improved workability during assembly. In addition, a complicated slit is not required. A hole is simply created in the battery lead plate  80  to serve as the lead opening  81 . Thus, the manufacturing and processing costs for electrode lead plates can be reduced. 
     The other end of the lead pin  90  is secured to a pin securing hole  74   a  formed beforehand in the pack circuit board  74 . As shown in the top view of  FIG. 10 , the lead engaging end  91  of the lead pin  90  is arranged so that it protrudes towards the lead opening  81 . The length of the lead pin  90  from the pin securing hole  74   a  to the lead engaging end  91  is designed to be roughly equal to the distance from the pin securing hole  74   a  to the battery lead plate  80 . When the lead engaging end  91  is inserted into the lead opening  81  in this way, the lead engaging end  91  is pushed from above the battery lead plate  80  as indicated by the dotted lines in  FIG. 16  using the pin securing hole  74   a  as the pivot point. This elastically deforms the lead engaging end  91  which then protrudes from the lead opening  81 . This operation is not complicated as in  FIG. 15  where the lead engaging end  91  is elongated and pushed back into a slit. In this simple operation, the lead engaging end  91  is simply pushed down, and the lead engaging end  91  inserts itself into the lead opening  81 . This greatly improves workability. Because the length of the lead engaging end  91  is less than the width of the lead opening  81 , the lead engaging end  91  can be elastically and easily pushed into the lead opening  81 . 
     (Guiding Rib  79 ) 
     In addition, a guiding rib  79  can be provided to guide the lead engaging end  91  into the lead opening  81  in the battery lead plate  80 . The following is an explanation of this arrangement with respect to  FIG. 17  through  FIG. 20 .  FIG. 17  is an enlarged view of portion XVII of the battery holder in  FIG. 10  in which a lead pin  90  has been inserted into a lead hole in the battery lead plate  80 .  FIG. 18  is a vertical cross-sectional view of the battery holder  70  from line XVIII-XVIII in  FIG. 10 .  FIG. 19  is an enlarged cross-sectional view of portion XIX in  FIG. 18  showing a guiding rib  79 .  FIG. 20  is an enlarged perspective view showing a portion of the battery pack in  FIG. 10  in which a lead pin  90  has been inserted into the lead hole using the guiding rib  79 . As shown in these drawings, the battery holder  70  is provided with a guiding rib  79  with an inclined surface in the battery lead plate  80  extending towards the lead opening  81 . As shown in the cross-sectional view of  FIG. 19 , the guiding rib  79  has an inclined surface or downward slope which extends towards the outside, that is, towards the battery lead plate  80 . Also, as shown in the top view of  FIG. 17 , there are two guiding tabs for each lead opening  81 . In this way, as shown in the perspective view of  FIG. 20  and the side view of  FIG. 16 , the lead pin  90  can be guided into the lead opening  81  using the guiding rib  79  so that the insertion operation is quick and reliable. 
     (Positioning of Pack Circuit Board  74  and Lead Pin  90 ) 
     The following is an explanation of the securing structure for the lead pin  90  and the pack circuit board  74  with reference to  FIG. 21  through  FIG. 27 .  FIG. 21  is a vertical cross-sectional view of the battery holder  70  from line XXI-XXI in  FIG. 11 .  FIG. 22  is an enlarged cross-sectional view of portion XXII of the battery holder in  FIG. 21  in which a lead pin  90  has been secured in a pin securing hole  74   a .  FIG. 23  is a top view showing a battery holder  70 Y of the prior art.  FIG. 24  is an enlarged view of portion XXIV of the battery holder in  FIG. 23  in which a lead pin  90 Y has been secured in a pin securing hole  74   x .  FIG. 25  is an exploded perspective view showing the lead pin  90 Y in  FIG. 24  being secured in a pin securing hole  74   x .  FIG. 26  is an enlarged view of portion XXVI of the battery holder in  FIG. 10  in which a lead pin  90  has been secured in a pin securing hole  74   a .  FIG. 27  is an exploded perspective view showing the lead pin  90  in  FIG. 26  being secured in a pin securing hole  74   a.    
     In the prior art, a lead pin  90 Y bent into a complicated shape as shown in  FIG. 25  is secured as shown in  FIG. 23  using a pin securing hole  74   x  and a pin securing slit  74   y  formed in the pack circuit board  74 Y as shown in  FIG. 24 . In other words, only one end of the lead pin is secured to the pack circuit board. Because the positioning and direction are indeterminate, a pin securing slit  74   y  is opened in the pack circuit board  74 Y, and a portion of the lead pin  90 Y is bent into a shape that allows it to be inserted into the pin securing slit  74   y . In this configuration, a pin securing slit  74   y  has to be opening in the pack circuit board  74 Y. Also, a portion of the lead pin  90 Y has to be bent in accordance with the pin securing slit  74   y . This processing is time-consuming. 
     The example of the present invention uses the pack circuit board  74  and lead pin  90  shown in  FIG. 26  and  FIG. 27  to position and secure the lead pin  90  in a predetermined position using a simpler structure. First, as shown in  FIG. 26 , the pack circuit board  74  has a pin engaging portion  74   b  formed on the edge of the pack circuit board  74  near the pin securing hole  74   a . As shown in  FIG. 27 , the end of the lead pin  90  opposite the end with the lead engaging end  91  is bent so as to be substantially parallel to the edge, and then bent into a C-shape (U-shape) to form a pin securing end  92 . The width of the bent portion of the pin securing end  92  is aligned with the width of the pin securing hole  74   a  and the pin engaging portion  74   b  of the pack circuit board  74 . Thus, as shown in  FIG. 22 , the lead pin  90  can be bent so that the pin securing end  92  is inserted and secured in the pin securing hole  74   a , and the C-shaped bent portion engages the pin engaging portion  74   b . In other words, the lead pin  90  can be positioned so that the pin securing end  92  bridges the pin securing hole  74   a  and the pin engaging portion  74   b , thereby making the lead pin  90  easy to insert into the pack circuit board  74 . The processing of the pack circuit board is much simpler because a pin securing slit does not have to be opened in the pack circuit board. A pin engaging portion  74   b  is simply formed in a portion of the edge. Manufacturing costs can also be reduced because the bent portion of the lead pin  90  has a simpler configuration. 
     The battery pack of the present invention can be used as a battery pack for operating battery-operated machinery such as a power tool, or as a battery pack for operating mobile equipment and devices such as a motor-assisted bicycle, an electric bicycle, or a mobile phone.