Patent Publication Number: US-9899645-B2

Title: Battery pack

Description:
This application is a Continuation Application of U.S. patent application Ser. No. 15/134,782 filed Apr. 21, 2016, which is a Continuation Application of U.S. patent application Ser. No. 14/459,457 filed Aug. 14, 2014, which is a Continuation of U.S. application Ser. No. 13/860,208, now U.S. Pat. No. 9,196,879, filed Apr. 10, 2013, which is a Continuation of PCT Application No. PCT/JP2011/073073 filed Oct. 6, 2011, which claims priority from Japanese Application No. 2010-290018 filed Dec. 27, 2010 and Japanese Application No. 2010-247214 filed Nov. 4, 2010. The disclosure of each of the earlier applications is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention relates to a battery pack configured to be capable of being mounted to a tool body of an electric tool as a power source of the electric tool. 
     BACKGROUND ART 
     In the related art, an electric tool includes a tool body driven by electric power, and a battery pack that serves as a power source for the tool body. The battery pack is configured to be detachably mounted to the tool body. The battery pack includes a housing case that forms an exterior cover, and a battery body that is installed in the housing case. The battery body includes a plurality of battery cells that can be charged and discharged, and a control board that controls the charge and discharge operations. Lead plates are connected to electrodes of the plurality of battery cells so that the battery cells are electrically connected in series or in parallel to each other. 
     Meanwhile, there may be an occasion that the afore-mentioned electric tool is used outdoors. Therefore, water such as raindrops may be splashed on such a battery pack, so that water may enter into the housing case. Here, when water enters into the housing case to cause the above-mentioned lead plates to be soaked in the water, unintended lead plates may be electrically connected to each other to the result that electricity, which is charged in battery cells, leaks. 
     For this reason, among battery packs, a battery pack has been known that is provided with a drain hole at a bottom portion of a housing case in order to discharge the water, which has been entered into the housing case, to the outside of the housing case (for example, see JP-A-2006-196277). According to this battery pack, it is possible to drain the water, which has been entered into the housing case, to the outside of the housing case from the drain hole, and therefore, it is possible to avoid the soaking of the lead plates in water, so that electricity charged in the battery cells may not leak. 
     Incidentally, in order to improve the drainage effect described above, it has been considered to provide a plurality of the drain holes formed at the bottom portion of the housing case. 
     However, if the plurality of drain holes are merely formed at the bottom portion of the housing case, conversely, water or dust may easily enter into the housing case from the drain holes. For this reason, it is preferable that the number of the drain holes is as small as possible, while the drainage effect described above is enhanced. 
     It is an object of the invention to provide a battery pack that is configured to be capable of being mounted on a tool body of an electric tool as a power source of the electric tool, can efficiently drain water having been introduced into a housing case to the outside of the housing case so as to prevent the leakage of the electricity charged in battery cells, and can make the number of drain holes be as small as possible. 
     SUMMARY OF THE INVENTION 
     In one aspect according to the present teachings, a battery pack may include a drainage device provided at a bottom portion of the housing case. The drainage device may include a drain hole communicating between inside and outside of the housing case, so that water introduced into the housing case is discharged to the outside of the housing case. The drainage device may be disposed at least between two of terminal members that are connected to electrodes of the battery cells. 
     According to a first embodiment, there is provided a battery pack configured to be able to be mounted on a tool body of an electric tool as a power source of the electric tool. The battery pack has a housing case forming an outer cover and a plurality of battery cells disposed in the housing case. A drainage function-shape portion is provided at a bottom portion of the housing case and includes a drain hole communicating with the inside of the housing case and the outside of the housing case for discharging water, which has been introduced into the housing case, to the outside of the housing case. An arrangement position of the drainage function-shape portion is set to be present at least between terminal members connected to electrodes of the battery cells. 
     Here, the drainage function-shape portion may include a drain hole communicating between the inside of the housing case and the outside of the housing case. This means that the drainage function-shape portion may be formed of only the drain hole or may include the drain hole and a structure that guides water to the drain hole. 
     According to the battery pack of the first embodiment, since the arrangement position of the drainage function-shape portion, which is disposed at the bottom portion of the housing case, is set to be present at least between the terminal members connected to the electrodes of the battery cells, it is possible to discharge water, which is present between the terminal members, to the outside of the housing case from the inside of the housing case. Accordingly, it is possible to drain water so that water presented at least between the terminal members is removed. As a result, it is possible to prevent the electrical connection between the terminal members, which may be caused when the terminal members soak in water. That is, even in the case that an appropriate rib shape is formed in the housing case for supporting the battery cells, it is possible to prevent electrical connection, which may be caused when at least the terminal members soak in the water, while allowing a puddle to be formed by the rib shape. 
     Accordingly, it is possible to prevent unintended electrical connection between the terminal members, which may be caused when the terminal members become soaked in water. That is, it is possible to efficiently drain water, which has been introduced into the housing case, to the outside of the housing case so that leakage of the electricity charged in the battery cells is prevented. Further, since the drain holes to be arranged are suppressed to minimal positions where the unintended electrical connection between the terminal members can be prevented, it is possible to make the number of drain holes be as small as possible. 
     According to a second embodiment, in the battery pack according to the first aspect, the terminal members, between which the arrangement position of the drainage function-shape portion is set, are terminal members that have a mutually adjacent arrangement relationship along an adjacently arranged direction of the electrodes of the plurality of battery cells. The battery cells are arranged in parallel so that the electrodes are arranged adjacent to each other, and have electrical potentials different from each other. 
     With the battery pack of the second embodiment, the terminal members, between which the arrangement position of the drainage function-shape portion is set, are terminal members which have a mutually adjacent arrangement relationship and have electrical potentials different from each other. Accordingly, a position where water is to be drained, can be set to be between the terminal members having a mutually adjacent arrangement relationship and have electrical potentials different from each other. Therefore, it is possible to set a position where it is desirous to drain and remove water for maintaining an insulation state, to a position where a short circuit between the terminal members is apt to occur, so that it is possible to more reliably prevent a short circuit, which may be caused when the terminal members soak in water. 
     According to a third embodiment, in the battery pack according to the first or second embodiment, an outer end edge of the drain hole disposed on an outer side of the housing case is formed and set to have a shape so that the outer end edge rises toward the inside of the housing case as compared to at least a peripheral portion of the outer end edge. 
     With the battery pack of the third embodiment, the outer end edge of the drain hole disposed on an outer side of the housing case is formed and set to have a shape so that the outer end edge rises toward the inside of the housing case as compared to at least the peripheral portion of the outer end edge. Accordingly, even in the case that the battery pack mounted on the tool body is placed on a desk or the ground and the bottom portion of the battery pack comes into contact with a placement surface of the desk or the ground, the outer end edge of the drain hole is positioned above the placement surface. Therefore, since it is possible to prevent the drain hole from being closed by the placement surface, it is possible to discharge the water, which is introduced into the housing case, to the outside of the housing case from the drain hole. 
     In addition, since it is possible to form at least a small clearance between the outer end edge of the drain hole and the placement surface, it is possible to easily guide the water, which is present in the housing case, to the outside of the housing case by utilizing the surface tension of the water introduced into the clearance. Accordingly, it is possible to efficiently drain the water, which has been introduced into the housing case, to the outside of the housing case. 
     According to a fourth embodiment, in the battery pack according to any one of the first to third embodiments, the drainage function-shape portion includes a flow guide device for guiding the flow of water so that water flows toward the drain hole, and the flow guide device is formed as a drain passage, so that the bottom portion of an inner side of the housing case is inclined downward toward the lower side of the bottom portion along a direction toward the drain hole. 
     With the battery pack of the fourth embodiment, since the flow guide device is formed as a drain passage, so that the bottom portion of an inner side of the housing case is inclined downward toward the lower side of the bottom portion along a direction toward the drain hole, it is possible to make the water, which has been introduced into the housing case, flow toward the drain hole by the inclined structure of the drain passage. Accordingly, it is possible to improve the drainage performance of not only the periphery of the drain hole but also a portion forming the drain passage, so that it is possible to expand a range, for which it is desired to improved the drainage performance. 
     Meanwhile, the arrangement portion where the drain passage is arranged may be present between the terminal members that are connected to the electrodes of the battery cells, or may be present at a position other than the position between the terminal members. Further, the drain passage may be formed to be inclined relative to the inner surface of the bottom portion, and may be formed flush with the outer surface of the bottom portion. 
     According to a fifth embodiment, in the battery pack according to any one of the first to fourth embodiments, the drainage function-shape portion includes a draw guide device for guiding the draw of water so that water is collected toward the drain hole, and the draw guide device is formed as a drawing groove that extends in a concave groove shape along an inner surface of the housing case from an inner end edge of the drain hole disposed on an inner side of the housing case, and acts so as to draw water toward the drain hole. 
     With the battery pack of the fifth embodiment, the draw guide device is formed as a drawing groove that extends in a concave groove shape along an inner surface of the housing case from an inner end edge of the drain hole disposed on an inner side of the housing case, and acts so as to draw water toward the drain hole. 
     Accordingly, it is possible to make the complete drainage of the water, which is present between the terminal members, so as to affect to the peripheral portion of the drain hole. Therefore, it is possible to more reliably prevent the electrical connection between the terminal members, which may be caused when the terminal members are soaked in water. 
     According to a sixth embodiment, in the battery pack according to any one of the first to fifth embodiments, a foreign material-introduction restricting rib is provided in the housing case so as to cross an opening shape of the drain hole in the housing case while maintaining an opened state of the drain hole. 
     With the battery pack of the sixth embodiment, the foreign material-introduction restricting rib is provided in the housing case so as to cross an opening shape of the drain hole in the housing case. Accordingly, even in the case that foreign materials are likely introduced into the housing case from the outside of the housing case through the drain hole, it is possible to hinder the introduction of the foreign materials by the foreign material-introduction regulating rib. Therefore, it is possible to maintain a clean inside of the housing case. 
     According to a seventh embodiment, in the battery pack according to any one of the first to sixth embodiments, an arrangement position of the drain hole is set to be present between the terminal members, and an arrangement position of any one or both of the flow guide device and the draw guide device is set to a position that is different from the position set between the terminal members. According to the battery pack of the seventh aspect, since the arrangement position of the drain hole is set to be present between the terminal members, it is possible to drain the water, which is present between the terminal members, to the outside of the housing case from the inside of the housing case. Accordingly, it is possible to guide the water, which is present in the vicinity of the drain hole, to the drain hole by the flow guide device or the draw guide device and to completely remove the water, which is present between these terminal members, by the presence of the drain hole. Therefore, it is possible to reliably prevent the unintended electrical connection between the terminal members. 
     According to an eighth embodiment, in the battery pack according to any one of the first to sixth embodiments, at least a part of any one or both of the flow guide device and the draw guide device is set to be present between the terminal members, and an arrangement position of the drain hole is set to a position that is different from the position set between the terminal members. 
     With the battery pack of the eighth embodiment, the arrangement position of the drain hole is set to a position that is different from the position set between the terminal members, and at least a part of any one or both of the flow guide device and the draw guide device is set to be present between the terminal members. Accordingly, the arrangement position of the drain hole can be set to a suitable portion of the housing case according to the design of the battery pack, while it is possible to drain water, which is present between these terminal members, to the outside of the housing case from the inside of the housing case. Therefore, it is possible to increase the degree of freedom of the arrangement position of the drain hole, so that it is also possible to increase the degree of freedom in the design of the battery pack. 
     Further, according to a ninth embodiment, in the battery pack according to the first embodiment, the housing case forming the outer cover of the battery pack is provided with a communication opening that communicates with the inside of the housing case from the outside of the housing case, and the housing case is provided with a water-introduction restricting portion that restricts the introduction of water, which is present in the vicinity of the communication opening, into the communication opening. 
     With the battery pack of the ninth embodiment, the housing case is provided with a water-introduction restricting portion that restricts the introduction of the water, which is present in the vicinity of the communication opening, into the communication opening, and therefore, the water-introduction regulating portion can restrict the introduction of water into the communication opening. Accordingly, it is possible to improve the waterproof property of the battery pack by restricting the intrusion of water into the housing case from the outside of the housing case. 
     According to a tenth embodiment, in the battery pack according to the ninth aspect, the water-introduction restricting portion is configured to have an inclined structure that makes water, which is present in the vicinity of the communication opening, flow in a direction away from the communication opening. 
     With the battery pack of the tenth embodiment, since the water-introduction restricting portion is configured to have an inclined structure that makes water, which is present in the vicinity of the communication opening, flow in a direction away from the communication opening, it is possible to make the water, which is present in the vicinity of the communication opening, flow in the direction away from the communication opening by the inclined structure of the water-introduction restricting portion. Accordingly, it is possible to restrict the introduction of water into the housing case from the outside of the housing case by isolating water from the communication opening, so that it is possible to improve the waterproof property of the battery pack. 
     According to an eleventh embodiment, in the battery pack according to the tenth embodiment, a battery-side connection terminal that is electrically connected to a connection terminal provided on a mounting target when the battery pack is mounted on the mounting target such as the tool body, wherein the communication opening is positioned at an arrangement portion where the battery-side connection terminal is arranged, and the water-introduction restricting portion is set for the periphery of the arrangement portion of the battery-side connection terminal, which is set to be the vicinity of the communication opening. The mounting target may be, for example, a tool body that is driven by the electric power, or a dedicated charger that is used during charging. 
     With the battery pack of the eleventh embodiment, since the water-introduction restriction portion is set for the periphery of the arrangement portion of the battery-side connection terminal, it is possible to make the water, which is present in the vicinity of the arrangement portion of the battery-side connection terminal, flow in the direction away from the periphery of the arrangement portion of the battery-side connection terminal using the inclined structure of the water-introduction restricting portion. Accordingly, it is possible to separate water from the arrangement portion of the battery-side connection terminal, and therefore, it is possible to improve the waterproof property of the battery pack by restricting the intrusion of water into the housing case from the outside of the housing case, so that it is possible to make the contact between water such as raindrops and the battery-side connection terminal more difficult. 
     According to a twelfth embodiment, the water-introduction restricting portion is formed in an uneven shape that isolates the water, which is present in the vicinity of the communication opening, from the communication opening. 
     With the battery pack of the twelfth embodiment, since the water-introduction restricting portion is formed in an uneven shape that isolates the water, which is present in the vicinity of the communication opening, from the communication opening, it is possible to isolate water, which is present in the vicinity of the communication opening, from the communication opening by the uneven shape of the water-introduction restricting portion. Accordingly, it is possible to restrict the intrusion of water into the housing case from the outside of the housing case by isolating water from the communication opening, so that it is possible to improve the waterproof property of the battery pack. 
     Here, the “uneven shape” may include, for example, a convex wall structure having ribs in the shape of a protrusion, a concave groove, or any appropriate uneven step shape, or the like. It may also include any of a concave shape, a convex shape, and an uneven shape that function to isolate the water, which is present in the vicinity of the communication opening, from the communication opening. 
     In a thirteenth embodiment, constructed similar to a battery pack of the twelfth embodiment, a male hook portion is fitted to a female hook portion provided on a mounting target when the battery pack is mounted on a mounting target such as the tool body. The communication opening is set to an arrangement portion where the male hook portion is arranged, and the water-introduction restricting portion is provided as the periphery of the arrangement portion of the male hook portion. Such water-introduction restricting portion is set to be the vicinity of the communication opening. 
     With the battery pack of the thirteenth embodiment, since the water-introduction restricting portion is provided for on the periphery of the arrangement portion of the male hook portion, it is possible to isolate the water, which is present in the periphery of the arrangement portion of the male hook portion, from the arrangement portion of the male hook portion, by the uneven shape of the water-introduction restricting portion. Accordingly, it is possible to restrict the introduction of water into the housing case from the outside of the housing case by isolating water from the arrangement portion of the male hook portion, so that it is possible to improve the waterproof property of the battery pack. 
     According to a fourteenth embodiment, in the battery pack according to the twelfth embodiment, there is provided a vent hole through which air flows into the housing case from the outside of the housing case, wherein the communication opening is set to an arrangement portion where the vent hole is arranged. The water-introduction restricting portion is provided on the periphery of the arrangement portion of the vent hole, which is set to be the periphery of the communication opening. 
     With the battery pack of the fourteenth embodiment, since the water-introduction restricting portion is provided on the periphery of the arrangement portion of the vent hole, it is possible to isolate the water, which is present in the periphery of the arrangement portion of the vent hole, from the arrangement portion of the vent hole by the uneven shape of the water-introduction restricting portion. Accordingly, it is possible to restrict the introduction of water into the housing case from the outside of the housing case by isolating water from the arrangement portion of the vent hole portion, so that it is possible to improve the waterproof property of the battery pack. 
     Advantageous Effects of Embodiments 
     According to the battery pack of the first embodiment, it is possible to efficiently drain water, which has been introduced into the housing case, to the outside of the housing case so as to prevent the leakage of the electricity charged in battery cells, and to make the number of drain holes be as small as possible. 
     According to the battery pack of the second embodiment, it is possible to set a position, for which it is desirous to maintain an insulation state, to a position where a short circuit between the terminal members easily occurs, and therefore, it is possible to more reliably prevent a short circuit. 
     According to the battery pack of the third embodiment, it is possible to prevent the drain hole from being closed by the placement surface, and therefore, it is possible to easily guide the water, which is present in the housing case, to the outside of the housing case. 
     According to the battery pack of the fourth embodiment, it is possible to improve the drainage performance of not only the periphery of the drain hole but also a portion forming the drain passage, so that it is possible to expand a range, for which it is desired to improved the drainage performance. 
     According to the battery pack of the fifth embodiment, it is possible to more reliably prevent the electrical connection between the terminal members, which may be caused when the terminal members soak in water. 
     According to the battery pack of the sixth embodiment, it is possible to maintain the inside of the housing case clean. 
     According to the battery pack of the seventh embodiment, it is possible to completely remove water, which is present between the terminal members, by the presence of the drain hole, so that it is possible to reliably prevent the unintended electrical connection between the terminal members. 
     According to the battery pack of the eighth embodiment, it is possible to increase the degree of freedom of the arrangement position of the drain hole, so that it is also possible to increase the degree of freedom in the design of the battery pack. 
     According to the battery pack of the ninth embodiment, it is possible to restrict the introduction of water into the housing case from the outside of the housing case, so that it is possible to improve the waterproof property of the battery pack. 
     According to the battery pack of the tenth embodiment, it is possible to restrict the introduction of water by isolating water from the communication opening, so that it is possible to improve the waterproof property of the battery pack. 
     According to the battery pack of the eleventh embodiment, it is possible to improve the waterproof property of the battery pack, so that it is possible to make the contact between water such as raindrops and the battery-side connection terminal more difficult. 
     According to the battery pack of the twelfth embodiment, the introduction of water into the housing case from the outside of the housing case is restricted by isolating water from the communication opening. Accordingly, the waterproof property of the battery pack is improved. 
     According to the battery pack of the thirteenth embodiment, the introduction of water is restricted by isolating water from the arrangement portion of the male hook portion. Accordingly, the waterproof property of the battery pack is improved. 
     According to the battery pack of the fourteenth embodiment, the introduction of water is restricted by isolating water from the arrangement portion of the vent hole. Accordingly, the waterproof property of the battery pack is improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an exploded perspective view of a battery pack of a first embodiment that is embodied in a first example. 
         FIG. 2  is a bottom view of the battery pack of  FIG. 1  when seen from the bottom. 
         FIG. 3  is a cross-sectional view of the battery pack taken along line III-III in  FIG. 2 . 
         FIG. 4  is a cross-sectional view of the battery pack taken along line IV-IV in  FIG. 2 . 
         FIG. 5  is a cross-sectional view of the battery pack taken along line V-V in  FIG. 2 . 
         FIG. 6  is an enlarged cross-sectional view of an arrangement portion of a case body of  FIG. 5  where a drain hole is arranged. 
         FIG. 7  is a top view of the case body that is seen from the top so that the inside of the case body is seen. 
         FIG. 8  is an enlarged top view of the arrangement portion of the case body where the drain hole is arranged. 
         FIG. 9  is a cross-sectional view of a battery pack showing an example where drain passages are provided. 
         FIG. 10  is an enlarged top view of the drain hole showing an example where drawing grooves are provided. 
         FIG. 11  is a perspective view of the case body that is seen in perspective so that the inside of the case body is seen. 
         FIG. 12  is a cross-sectional view of the case body taken along line XII-XII in  FIG. 11 . 
         FIG. 13  is a perspective view of the appearance of a battery pack of a third embodiment that is embodied in a second example. 
         FIG. 14  is a top view of the battery pack of  FIG. 13 . 
         FIG. 15  is a cross-sectional view of the battery pack taken along line XV-XV in  FIG. 14 . 
         FIG. 16  is a cross-sectional view of the battery pack taken along line XVI-XVI in  FIG. 14 . 
         FIG. 17  is an enlarged cross-sectional view of the upper surface of the battery pack shown in  FIG. 16 . 
         FIG. 18  is a perspective view of the appearance of a battery pack of a fourth embodiment that is embodied in the second example. 
         FIG. 19  is a top view of the battery pack of  FIG. 18 . 
         FIG. 20  is a cross-sectional view taken along line XX-XX in  FIG. 19 . 
         FIG. 21  is a cross-sectional view taken along line XXI-XXI in  FIG. 19 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First and second embodiments, which are embodied in a first example shown in  FIGS. 1 to 12 , will be described below. 
     First Embodiment 
     The first embodiment, which embodies a battery pack according to the invention, will be described below with reference to  FIGS. 1 to 10 . 
     An exploded perspective view of  FIG. 1  shows a battery pack  10  of a first embodiment that is embodied in a first example. This exploded perspective view shows the battery pack  10  so that the inside of a battery pack body  40  is seen. Meanwhile, in the following description, an electrical connection side of the battery pack  10  will be defined as the upper side and a slide mounting direction of the battery pack  10  will be defined as a forward direction. 
     The battery pack  10  is configured to be detachably mounted by sliding onto a tool body (mounting target) of an electric tool that is typified by, for example, an electric screwdriver. The battery pack  10  serves as a drive power source of the tool body having on the battery pack  10  mounted thereon. For this reason, when the charge amount of the battery pack  10  is reduced, the battery pack  10  is removed from the tool body and charged by a dedicated external charger (mounting target), and when it is completely charged by the dedicated charger, the battery pack  10  is remounted on the tool body and functions as a drive power source. 
     As shown in the exploded perspective view of  FIG. 1 , the battery pack  10  generally includes a housing case  20  and a battery pack body  40 . The housing case  20  is formed in the shape of a case in which the battery pack body  40  is disposed and which forms an outer cover. Further, the battery pack body  40  is mounted within the housing case  20 . 
     Prior to the description of the housing case  20 , the structure of the battery pack body  40  will be described. 
     The battery pack body  40  is disposed in the housing case  20  described in detail below and generally includes a plurality of battery cells  41 , a connection control board  51 , and a male hook mechanism  55  as shown in  FIG. 1 . 
     The battery cells  41  are battery cells that are broadly used and can be charged and discharged. As shown in  FIG. 1 , the battery cells  41  of the battery pack body  40  are disposed in parallel so that a total of ten battery cells  41  form two stages each of which includes five battery cells and electrodes  42  of the battery cells  41  are adjacent to each other. Specifically, a total of ten battery cells  41  are arranged side by side to form two stages each having five battery cells, so that the electrodes  42  of the battery cells  41  are positioned on both the left and right sides of the battery pack. Meanwhile, for the purpose of explanation of the battery cells  41  arranged side by side in this way, the battery cells  41  are denoted by reference numerals as a first battery cell  410 , a second battery cell  411 , a third battery cell  412 , a fourth battery cell  413 , . . . in this order from the upper side and the front side of the battery pack  10 . Further, a lead base end of a lead wire of the electrode  42  of each battery cell  41 , which is shown in the drawing, is shown as a circular mark in a lead plate  45 . However, this lead wire is led from an end portion of the battery cell  41  that is positioned at the circular mark of the lead plate  45 . 
     The electrodes  42  of the battery cells  41 , which have been arranged side by side as described above, are positioned at both left and right ends of the battery pack  10 . That is, ten electrodes  42  of the respective battery cells  41  are positioned at each of both left and right ends of the battery pack  10 . Lead plates  45 , which are to be electrically connected, are mounted on the respective electrodes  42  of these battery cells  41 . Specifically, left lead plates  46 , which are electrically connected, are mounted on the electrodes  42 , which are positioned at the left ends, of the ten battery cells  41 ; right lead plates  47 , which are electrically connected, are mounted on the electrodes  42 , which are positioned at the right ends, of the ten battery cells  41 . These left and right lead plates  46  and  47  correspond to terminal members according to the invention, and function as plate-like terminals that are broadly used. Moreover, the other sides of the lead plates  45  (the left and right lead plates  46  and  47 ) of which one sides are connected to the electrodes  42  of the battery cells  41  in this way are electrically connected to the connection control board  51  that will be described below. Meanwhile, these left and right lead plates  46  and  47  will be described in detail later. 
     Next, the connection control board  51  and the male hook mechanism  55  will be described. 
     The connection control board  51  is electrically connected to the battery cells  41  that can be charged and discharged, and controls the charge and discharge of the battery cells  41 . That is, the connection control board  51  is disposed above the above-mentioned plurality of battery cells  41 , and generally includes a control board  52  and connection terminal portions  53  that are provided on the control board  52 . The control board  52  performs appropriate electrical controls when the battery cells  41  are charged and discharged. The connection terminal portions  53  serve as terminals that are electrically connected to a tool body or a dedicated charger (not shown) serving as a mounting target. That is, the connection terminal portions  53  include three kinds of connection terminals, that is, a positive connection terminal  531  that is connected to a positive terminal of, for example, the tool body serving as the mounting target; a negative connection terminal  532  that is connected to a negative terminal of, for example, the tool body; and a control connection terminal  533  that is connected to a control terminal of, for example, the tool body. Meanwhile, these connection terminal portions  53  are formed by leaf spring-type metal terminals that are disposed so as to face each other. 
     The male hook mechanism  55  has the structure that is removably locked to the tool body when sliding to be mounted on, for example, the tool body serving as the above-mentioned mounting target. For this reason, the male hook mechanism  55  has a hook shape for locking to the tool body and a finger-engaging shape for a release operation. Specifically, the male hook mechanism  55  includes a hook-type structure  56  that has the hook shape and the finger-engaging shape and a biasing spring  57  that biases the hook-type structure  56  in a locking direction. The male hook mechanism  55  having the above-mentioned structure automatically locks the hook-type structure  56  to the tool body by a biasing force of the biasing spring  57  when slid to be mounted on the tool body. Further, when a release operation is performed against the biasing force of the biasing spring  57 , the locking of the hook-type structure  56  to the tool body is released. When the battery pack  10  is slid in this state, the male hook mechanism  55  can be removed from the tool body. 
     Next, the above-mentioned left and right lead plates  46  and  47  will be described in detail. 
     The left and right lead plates  46  and  47  are formed of plate-like terminals, respectively, and are mounted over the electrodes  42  of the plurality of battery cells  41 , respectively. 
     A bottom view of  FIG. 2  shows the battery pack  10  that is seen from the bottom. A cross-sectional view of  FIG. 3  shows the cross-section of the battery pack  10  of  FIG. 2  taken along line III-III so that the left lead plates  46  positioned on the left side of the battery pack  10  are seen. A cross-sectional view of  FIG. 4  shows the cross-section of the battery pack  10  of  FIG. 2  taken along line IV-IV so that the right lead plates  47  positioned on the right side of the battery pack  10  are seen. 
     As shown in  FIG. 3 , the left lead plates  46  are formed of three plate-like terminals that are separated from each other. The three left lead plates  46  are denoted by reference numerals as a first left lead plate  461 , a second left lead plate  462 , and a third left lead plate  463  in this order from the front side. That is, as shown in  FIG. 3 , the first left lead plate  461  is mounted to extend between the two left electrodes  42  of the first battery cell  410  and the second battery cell  411  among ten electrodes  42  that are formed at the left ends of the battery cells  41 . Further, the second left lead plate  462  is mounted to extend between the four left electrodes  42  of the third battery cell  412 , the fourth battery cell  413 , the fifth battery cell  414 , and the sixth battery cell  415 . Furthermore, the third left lead plate  463  is mounted to extend between the four left electrodes  42  of the seventh battery cell  416 , the eighth battery cell  417 , the ninth battery cell  418 , and the tenth battery cell  419 . 
     Meanwhile, conversely, as shown in  FIG. 3 , the first and second left lead plates  461  and  462  are arranged and constructed to form a separate configuration such that the first and second battery cells  410  and  411  and the third and fourth battery cells  412  and  413  are not electrically connected to each other so as to be divided and separated from each other. According to the arrangement relationship between these left lead plates, the first and second left lead plates  461  and  462  adjacent to each other serve as the lead plates  45  of which the electrical potentials are different from each other. Further, the second and third left lead plates  462  and  463  are arranged and constructed to form a separate configuration such that the fifth and sixth battery cells  414  and  415  and the seventh and eighth battery cells  416  and  417  are not electrically connected to each other so as to be divided and separated from each other. According to the arrangement relationship between these left lead plates, the second and third left lead plates  462  and  463  adjacent to each other serve as the lead plates  45  of which the electrical potentials are different from each other. That is, individually, the left lead plates  46  ( 461 ,  462 , and  463 ) are arranged adjacent to each other along the direction where the electrodes  42  of the ten battery cells  41  disposed in parallel are adjacent to each other, and the electrical potentials of the left lead plates  46  are different from each other. 
     Moreover, as shown in  FIG. 4 , the right lead plates  47  are also formed of three plate-like terminals that are separated from each other. The three right lead plates  47  are denoted by reference numerals as a first right lead plate  471 , a second right lead plate  472 , and a third right lead plate  473  in this order from the front side. That is, as shown in  FIG. 4 , the first right lead plate  471  is mounted to extend between the four right electrodes  42  of the first battery cell  410 , the second battery cell  411 , the third battery cell  412 , and the fourth battery cell  413  among ten electrodes  42  that are formed at the right ends of the battery cells  41 . Further, the second right lead plate  472  is mounted to extend between the four right electrodes  42  of the fifth battery cell  414 , the sixth battery cell  415 , the seventh battery cell  416 , and the eighth battery cell  417 . Furthermore, the third right lead plate  473  is mounted to extend between the two right electrodes  42  of the ninth battery cell  418  and the tenth battery cell  419 . 
     Meanwhile, conversely, as shown in  FIG. 4 , the first and second right lead plates  471  and  472  are arranged and constructed to form a separate configuration such that the third and fourth battery cells  412  and  413  and the fifth and sixth battery cells  414  and  415  are not electrically connected to each other so as to be divided and separated from each other. According to the arrangement relationship between these right lead plates, the first and second right lead plates  471  and  472  adjacent to each other are formed of the lead plates  45  of which the electrical potentials are different from each other. Further, the second and third right lead plates  472  and  473  are arranged and constructed to form a separate configuration such that the seventh and eighth battery cells  416  and  417  and the ninth and tenth battery cells  418  and  419  are not electrically connected to each other so as to be divided and separated from each other. According to the arrangement relationship between these right lead plates, the second and third right lead plates  472  and  473  adjacent to each other are formed of the lead plates  45  of which the electrical potentials are different from each other. That is, individually, the right lead plates  47  ( 471 ,  472 , and  473 ) are also arranged adjacent to each other along the direction where the electrodes  42  of the ten battery cells  41  disposed in parallel are adjacent to each other, and the electrical potentials of the right lead plates  47  are different from each other. 
     Next, the housing case  20  in which the above-mentioned battery pack body  40  is disposed will be described. 
     The housing case  20  has a function as an outer cover case of the battery pack  10  and also has a function as a housing in which the battery pack body  40  is disposed. The housing case  20  includes a box-shaped case body  21  with an opened upper portion, and an upper cover member  31  that closes the opened upper portion of the case body  21  as an upper cover of the case body  21 . The case body  21  and the upper cover member  31  are fastened to each other by screw members  39 . 
     First, the upper cover member  31  of the housing case  20  will be described. 
     The upper cover member  31  serves as a connection-side outer cover of the housing case  20  when the battery pack  10  is slid to be mounted. That is, the upper cover member  31  is formed to have a structure capable of sliding to be mounted on the mounting target such as the tool body. Specifically, slide guide portions  32 , which guide the slide mounting, are formed at the middle portion of the upper cover member  31 . Further, the upper cover member  31  is provided with connection openings  33  that allow the terminals of the mounting target to be connected to the above-mentioned connection terminal portions  53  (the connection control board  51 ). The upper cover member  31  is provided with a hook-exposure opening  34  through which the hook-type structure  56  (the male hook mechanism  55 ) to be locked to the mounting target is exposed to the outside. The upper cover member  31  is provided with an air vent opening  35  through which air is sent to cool the inside of the housing case  20 . The air vent opening  35  includes a first air vent opening  36  through which cooling air is sent into the housing case  20  and second air vent openings  37  through which the cooling air sent into the housing case  20  is discharged to the outside of the housing case  20  after cooling the battery cells  41 . Meanwhile, the slide guide portions  32 , the connection openings  33 , and the like are formed to have shapes that cope with the slide mounting of the battery pack  10 . 
     Next, the case body  21  of the housing case  20  will be described. 
     A cross-sectional view of  FIG. 5  shows the cross-section of the battery pack  10  of  FIG. 2  taken along line V-V. A cross-sectional view of  FIG. 6  is an enlarged cross-sectional view of a portion (a portion that is marked with a circle shown in  FIG. 5  by a chain line) of the case body  21  of  FIG. 5  where a drain hole  25  is disposed. A top view of  FIG. 7  shows the case body  21  that is seen from the top so that the inside of the case body  21  is seen. A top view of  FIG. 8  enlarges and shows the portion (the portion that is marked with a circle shown in  FIG. 5  by a chain line) of the case body  21  of  FIG. 7  where the drain hole  25  is disposed. Meanwhile, in  FIGS. 5 and 6 , the battery pack  10  is placed on a placement surface F that forms a horizontal surface. 
     As also shown in  FIG. 1 , the case body  21  is formed in the shape of a box which is surrounded by one bottom wall portion  211  and four side wall portions  212  and of which the upper portion is opened so that the above-mentioned battery pack body  40  can be installed. Meanwhile, the bottom wall portion  211  of the case body  21  corresponds to a bottom portion according to the invention. As shown in  FIG. 5 , the case body  21  is formed so that the above-mentioned battery cells  41  can be installed in the case body  21 . An outer surface  221  of the bottom wall portion  211  of the case body  21  is formed substantially flush as shown in  FIG. 5 , while ribs  23 , which appropriately have concave and convex shapes, are provided on an inner surface  222  of the bottom wall portion. The ribs  23  have an appropriately uneven shape, and are formed so as to protrude toward the inside of the case body  21 . The ribs  23  are formed of three kinds of ribs, that is, support ribs  231 , air guide ribs  232 , and foreign material-introduction restricting ribs  233 . As shown in  FIGS. 5 and 6 , the support ribs  231  mainly function as ribs that support the battery cells  41  to be installed in order to stabilize the installation state of the battery cells  41  that are to be installed in the case body  21 . For this reason, the support ribs  231  are formed in the shapes of concave curved surfaces corresponding to the curved surface shapes of the outer peripheries of the battery cells  41  to be installed. Meanwhile, the support ribs  231  also contribute to improve the strength of the strength of the case body  21 . Further, as shown in  FIG. 6 , the air guide ribs  232  function as guides for guiding cooling air when cooling air is sent to the second air vent openings  37  from the first air vent opening  36  for cooling the battery cells  41 . For this purpose, the shapes of the air guide ribs  232  are selected so that air sent into the case body  21  can efficiently cool the battery cells  41 . Meanwhile, the air guide ribs  232  also have the same function as the above-mentioned support ribs  231 , that is, a function as ribs, which support the battery cells  41  to be installed, and the like. The foreign material-introduction restricting ribs  233  will be described after the description of the drain holes  25  that will be described next. 
     As shown in  FIGS. 3 and 4 , the case body  21  is provided with drain holes  25  having a function of discharging the water, which has been introduced into the housing case  20 , to the outside of the housing case  20 . Meanwhile, the drain holes  25  are included in a drainage function-shape portion according to the invention. The drain holes  25  are disposed at the bottom wall portion  211 , which forms the bottom portion of the housing case  20 , so that the inside and the outside of the housing case  20  communicate with each other. The arrangement positions of the drain holes  25  are set to be present between the lead plates  45 , which are connected to the electrodes  42  of the above-mentioned battery cells  41 , at the bottom wall portion  211  of the housing case  20 . For this reason, as understood from the comparison between  FIG. 2  and  FIGS. 3 and 4 , the drain holes  25  are disposed so as to be present between the four of the respective lead plates  45 . 
     Individually and specifically, at the left portion of the bottom wall portion  211  of the housing case  20 , a first drain hole  251  is disposed between the above-mentioned first and second left lead plates  461  and  462 ; a second drain hole  252  is disposed between the above-mentioned second and third left lead plates  462  and  463 . In contrast, at the right portion of the bottom wall portion  211  of the housing case  20 , a third drain hole  253  is disposed between the above-mentioned first and second right lead plates  471  and  472 ; a fourth drain hole  254  is disposed between the above-mentioned second and third right lead plates  472  and  473 . 
     That is, there are a total of four drain holes  25  disposed on the case body  21 . There are a total of six lead plates  45 , which means there are two fewer drain holes  25  than head plates  45 . There are ten total battery cells  41 , which means there are four fewer drain holes  25  than battery cells  41 . Meanwhile, as shown in  FIG. 8 , the shapes of these drain holes  25  are set to have a circular shape in top view, and the diameters of the drain holes  25  are set to 2.5 mm that is not an excessively large diameter. 
     In other words, the first drain hole  251  drains water that is present between the first and second left lead plates  461  and  462 , and the second drain hole  252  drains water that is present between the second and third left lead plates  462  and  463 . Further, the third drain hole  253  drains water that is present between the first and second right lead plates  471  and  472 , and the fourth drain hole  254  drains water that is present between the second and third right lead plates  472  and  473 . 
     Here, the respective drain holes  25  ( 251 ,  252 ,  253 , and  254 ) are set as described below and are disposed at the bottom wall portion  211  of the housing case  20 . The drain hole  25  will be described with reference to  FIGS. 6 and 8  that are enlarged views. Meanwhile, in the drain hole  25 , an opening end edge of the drain hole  25 , which is disposed at the outer portion of the housing case  20 , is set as an outer end edge  261 ; an opening end edge of the drain hole  25 , which is disposed at the inner portion of the housing case  20 , is set as an inner end edge  262 . That is, as shown in  FIG. 6 , the shape of the outer end edge  261  of the drain hole  25  ( 251 ) is set so that the outer end edge  261  slightly rises toward the inside of the housing case  20  as compared with a support lower surface  201  of the housing case  20  that corresponds to the peripheral portion of the outer end edge  261 . For this reason, a clearance C is formed between the outer end edge  261  and the placement surface F with which the support lower surface  201  of the housing case  20  corresponding to the peripheral portion of the outer end edge  261  comes into contact. 
     Further, the foreign material-introduction restricting ribs  233  are provided in the housing case  20 . That is, as shown in  FIG. 6 , the foreign material-introduction restricting rib  233  is provided at a position, which is spaced upward from the inner end edge  262  of the drain hole  25 , on a portion that is positioned above the inner end edge  262  of the above-mentioned drain hole  25 . That is, the foreign material-introduction restricting rib  233  is provided so as to be spaced upward from the inner end edge  262  of the drain hole  25  while the opened state of the drain hole  25  is maintained. Furthermore, as shown in  FIG. 8 , the foreign material-introduction regulating rib  233  is provided in the housing case  20  so as to cross the shape of the opening of the drain hole  25 . 
     According to the battery pack  10  having the above-mentioned structure, it is possible to obtain the following functions and effects. 
     That is, according to the above-mentioned battery pack  10 , since the arrangement positions of the drain holes  25  are set to be present between the lead plates  45  that are connected to the electrodes  42  of the battery cells  41 , it is possible to discharge the water, which is present between the lead plates  45 , to the outside of the housing case  20  from the inside of the housing case  20 . Accordingly, since it is possible to drain water so that the water present at least between the lead plates  45  is removed, it is possible to prevent the electrical connection between the lead plates  45 , which may be caused when the lead plates  45  soak in water. That is, even though appropriate ribs  23 , such as the support ribs  231  and the air guide ribs  232 , are formed in the housing case  20  so as to support the battery cells  41 , it is possible to prevent the electrical connection between the lead plates  45 , which may be caused when at least the lead plates  45  soak in the water, while allowing a puddle to be formed by the ribs  23 . Accordingly, it is possible to prevent the unintended electrical connection between the lead plates  45 , which may be caused when the lead plates  45  soak in water. That is, it is possible to efficiently drain the water, which has been introduced into the housing case  20 , to the outside of the housing case  20  so that the leakage of the electricity charged in the battery cells  41  is prevented. Further, since positions of the drain holes  25  to be disposed is suppressed to be minimum positions that can prevent the unintended electrical connection between the lead plates  45 , it is possible to make the number of holes for drainage be as small as possible. 
     Furthermore, according to the above-mentioned battery pack  10 , since the lead plates  45  between which the arrangement positions of the drain holes  25  are set are the lead plates  45  that are adjacent to each other and have different electrical potentials, it is possible to set a position, where water is drained so as to be removed, between the lead plates  45  that are adjacent to each other and have different electrical potentials. Accordingly, since it is possible to set a position, where water is to be drained so as to be removed and an insulation state is to be maintained, to a position where a short circuit between the lead plates  45  easily occurs, it is possible to more reliably prevent a short circuit that is caused when the lead plates  45  soak in water. 
     Moreover, according to the above-mentioned battery pack  10 , the shape of the outer end edge  261  of the drain hole  25 , which is disposed at the outer portion of the housing case  20 , is set so that the outer end edge  261  rises toward the inside of the housing case  20  as compared with the support lower surface  201  corresponding to at least the peripheral portion of the outer end edge  261 . Accordingly, even when the battery pack  10  mounted on the tool body (not shown) is placed on a desk or the ground such that the support lower surface  201 , which is the bottom portion of the battery pack  10 , comes into contact with the placement surface F, the outer end edge  261  of the drain hole  25  is positioned above the placement surface F by the clearance C. Therefore, it is possible to prevent the drain hole  25  from being closed by the placement surface F, and hence it is possible to discharge the water, which is introduced into the housing case  20 , to the outside of the housing case  20  from the drain hole  25 . In addition, since it is possible to form the small clearance C between the outer end edge  261  of the drain hole  25  and the placement surface F, it is possible to easily guide the water, which is present in the housing case  20 , to the outside of the housing case  20  by the surface tension of the water that has been introduced into the clearance C. Accordingly, it is possible to efficiently drain the water, which has been introduced into the housing case  20 , to the outside of the housing case  20 . 
     Further, according to the above-mentioned battery pack  10 , the foreign material-introduction restriction rib  233 , which crosses the shape of the opening of the drain hole  25  in the housing case  20 , is provided in the housing case  20 . Accordingly, even in the case of possible introduction of foreign materials into the housing case  20  from the outside of the housing case  20  through the drain hole  25 , it is possible to hinder the introduction of the foreign materials by the foreign material-introduction restricting rib  233 . Therefore, it is possible to maintain the inside of the housing case  20  clean. 
     Next, two modifications of the battery pack  10  of the first embodiment will be described with reference to  FIGS. 9 and 10 .  FIG. 9  is a cross-sectional view of a battery pack  10 A showing a modification where drain passages  27  are provided.  FIG. 10  is an enlarged top view of a drain hole  25 A showing a modification where drawing grooves  28  are provided. 
     The two modifications shown in  FIGS. 9 and 10  are examples where the arrangement positions of the drain holes  25  are set to be present between the lead plates  45  as described above. The two modifications are examples where a flow guide device or a draw guide mean device is provided at a position different from the position between the lead plates  45  where the arrangement positions of the drain holes  25  are set. 
     Meanwhile, the flow guide device and the draw guide device are included in the drainage function-shape portion according to the invention. The flow guide device and the draw guide device are formed by forming a shape, which has a function of discharging the water having been introduced into the housing case  20  to the outside of the housing case  20 , on the housing case  20 . 
     These modifications are different from the above-mentioned battery pack  10  in that the structure of the drain passages  27  as the flow guide device or the structure of the drawing grooves  28  as the draw guide device is provided. For this reason, this battery pack  10  configuration is the same as the above-mentioned battery pack  10  except for the different drain passage  27 . Accordingly, portions having the same structure as the structure of the portions of the above-mentioned battery pack  10  are denoted by the same reference numerals as the reference numerals used in the above-mentioned battery pack  10  or the same reference numerals that have “A” at the ends thereof and the description thereof will be omitted. 
     Meanwhile, in the modifications that will be described below, the arrangement positions of the drain holes  25  are set to be present between the lead plates  45  as in the above-mentioned battery pack  10 . In contrast, the structure of the drain passages  27  as the flow guide device or the structure of the drawing grooves  28  as the draw guide device is set at a position different from the position between the lead plates  45 . 
     First, a modification where the drain passages  27  are provided in the battery pack  10 A will be described. The battery pack  10 A shown in  FIG. 9  is provided with the drain passages  27  as the flow guide device. The drain passages  27  serve to guide the flow of water so that water flows toward the drain holes  25 . That is, the drain passages  27  are formed on a bottom surface  223  of the bottom wall portion  211  of the case body  21  that forms the inner surface  222  of the housing case  20 . The drain passage  27  is formed so that the bottom surface  223  is inclined downward toward the drain hole  25 . Specifically, on the bottom surface  223  that is positioned below the second left lead plate  462 , a front half of the drain passage is formed as a first drain passage  271  inclined downward toward the first drain hole  251 ; a rear half thereof is formed as a second drain passage  272  inclined downward toward the second drain hole  252 . That is, the bottom surface  223 , which is positioned below the second left lead plate  462 , is formed in the shape of a mountain, of which the bases extend forward and rearward from a portion positioned below the middle of the second left lead plate  462  as a peak. Further, on the bottom surface  223  that is positioned below the third left lead plate  463 , a front half of the drain passage is formed as a third drain passage  273  inclined downward toward the second drain hole  252 . That is, the bottom surface  223 , which is positioned below the third left lead plate  463 , is formed in the shape of the half of a mountain, of which the base extends forward from a portion positioned below the middle of the third left lead plate  463  as a peak. Meanwhile, the bottom surface  223 , which forms the inner surface  222 , of the bottom wall portion  211  of the case body  21  is formed obliquely; the outer surface  221 , which comes into contact with the above-mentioned placement surface F so as to be supported, is formed to be flush. 
     According to the battery pack  10 A of this modification, it is possible to obtain the following functions and effects in addition to the functions and effects that are obtained by the above-mentioned battery pack  10 . That is, according to the above-mentioned battery pack  10 A, since the drain passages  27  as the flow guide device are formed so that the bottom surface  223  of the housing case  20  is inclined downward toward the drain holes  25 , it is possible to make the water, which has been introduced into the housing case  20 , flow toward the drain holes  25  by the inclined structure of the drain passages  27 . Accordingly, it is possible to improve the drainage performance of not only the vicinity of the drain holes  25  but also portions forming the drain passages  27 , so that it is possible to expand a range that is desired to improve the drainage performance. Further, according to this battery pack  10 A, it is possible to guide the water, which is present in the peripheral portion of the drain holes  25 , to the drain holes  25  by the drain passages  27  as the flow guide device, while it is possible to completely remove the water, which is present between these lead plates  45 , by using the presence of the drain holes  25 . Accordingly, it is possible to reliably prevent the unintended electrical connection between the lead plates  45 . 
     Next, a modification where the drawing grooves  28  are provided at drain holes  25 A will be described. 
     The drain hole  25 A shown in  FIG. 10  is provided with the drawing grooves  28  as the draw guide device. The drawing grooves  28  serve to draw and guide water so that water is collected toward the drain hole  25 A. That is, the drawing grooves  28  act so as to draw water toward the drain hole  25 . In other words, the drawing grooves  28  are formed in a concave groove shape so as to radially extend on the inner surface  222  of the housing case  20  from the inner end edge  262  of the drain hole  25 . Specifically, five drawing grooves  28 , which radially extend in a concave groove shape, are formed in a peripheral portion, which is shown on the left side in the drawing, of the drain hole  25 A. The five drawing grooves  28  are appropriately cut into a surface of the peripheral portion so as to have a small depth and are formed at appropriate intervals from each other. 
     According to the drain hole  25 A of this modification, it is possible to obtain the following functions and effects in addition to the functions and effects that are obtained by the above-mentioned battery pack  10 . That is, since the drawing grooves  28  as the draw guide device are formed in a concave groove shape so as to radially extend on the inner surface  222  of the housing case  20  from the inner end edge  262  of the drain hole  25 , the drawing grooves  28  can act so as to draw the water, which is present in the peripheral portion of the inner end edge  262 , toward the drain hole  25 . For this reason, it is possible to make the complete drainage of the water, which is present between the lead plates  45 , so as to affect to the peripheral portion of the drain hole  25 A. Accordingly, it is possible to more reliably prevent the electrical connection between the lead plates, which may be caused when the above-mentioned lead plates  45  soak in water. Further, with the battery pack provided with the drain holes  25 A, it is possible to guide the water, which is present in the peripheral portion of the drain holes  25 , to the drain holes  25 A by the drawing grooves  28  as the draw guide device and to completely remove the water, which is present between these lead plates  45 , by using the presence of the drain holes  25 A. Accordingly, it is possible to reliably prevent the unintended electrical connection between the lead plates  45 . 
     Second Embodiment 
     Next, the second embodiment, which embodies the battery pack according to the invention, will be described with reference to  FIGS. 11 and 12 . Here, a perspective view of  FIG. 11  is a perspective view of a case body  21 B that is viewed in perspective so that the inside of the case body is seen. Further, a cross-sectional view of  FIG. 12  is a cross-sectional view of the case body  21 B of  FIG. 11  taken along line XII-XII. 
     That is, although the entire view is not shown, the battery pack of the second embodiment is different from the battery pack  10  of the above-mentioned first embodiment only in the structure of the case body  21 . That is, in the battery pack of the second embodiment, a part of the structure of a drain passage  27 B as a flow guide device is set to be present between the lead plates  45 ; a drain hole  25 B is set to a position different from the position between the lead plates  45  unlike in the modification of the above-mentioned first embodiment. 
     The second embodiment is different from the above-mentioned battery pack  10  in the arrangement structure of the drain passage  27 B used as a flow guide device and in the arrangement structure of the drain hole  25 B. For this reason, since the structure, except for these different structures, is the same as that of the above-mentioned battery pack  10 , the same reference numerals as the reference numerals described in the above-mentioned battery pack  10  are given in the drawings and the description of the same structure will be omitted. 
     That is, as shown in  FIGS. 11 and 12 , the bottom wall portion  211  of the case body  21 B corresponding to the bottom portion according to the invention is provided with the drain hole  25 B. As shown in  FIGS. 11 and 12 , the drain hole  25 B is formed substantially at the center of the bottom wall portion  211 . Like the above-mentioned drain hole  25 , the drain hole  25 B has a function of discharging the water, which has been introduced into the housing case  20 , to the outside of the housing case  20 . However, while the arrangement position of the drain hole  25  of the battery pack  10  of the above-mentioned first embodiment has been set to be present between the lead plates  45 , the arrangement position of the drain hole  25 B of the battery pack of the second embodiment is set to the middle of the bottom wall portion  211  with respect to a left and right direction. Like the above-mentioned drain hole  25 , the drain hole  25 B is disposed so that the inside and the outside of the housing case  20  communicate with each other. In contrast, the drain passage  27 B is formed on the bottom surface  223  of the bottom wall portion  211  of the case body  21 , which forms the inner surface  222  of the housing case  20 , so as to extend in the left and right direction of the case body  21 . Specifically, the drain passage  27 B is formed in the shape of a groove that is inclined downward toward the drain hole  25 B, which is formed substantially at the center of the bottom wall portion  211 , from a portion (a portion that is marked with a circle shown in  FIGS. 11 and 12  by a phantom line), where the first drain hole  251  of the above-mentioned first embodiment is disposed, as a peak. That is, the highest portion of the drain passage  27 B is set to be positioned between the above-mentioned first and second left lead plates  461  and  462  (corresponding to a position where the first drain hole  251  of the first embodiment is disposed). Further, the lowest portion of the drain passage  27 B is a portion where the drain hole  25 B is disposed. 
     According to the battery pack of the second embodiment, the arrangement position of the drain hole  25 B is set substantially to the center of the bottom wall portion  211  and a peak portion of the drain passage  27 B is set to be positioned between the first and second left lead plates  461  and  462  (corresponding to the position where the first drain hole  251  of the first embodiment is disposed). Accordingly, it is possible to drain the water, which is present between the lead plates  45 , to the outside of the housing case  20  from the inside of the housing case  20  and to set the arrangement position of the drain hole  25 B substantially to the center of the bottom portion of the housing case  20  according to the design of the battery pack. Therefore, it is possible to increase the degree of freedom of the arrangement position of the drain hole  25 B, so that it is also possible to increase the degree of freedom in the design of the battery pack. 
     Meanwhile, the battery pack according to the invention is not limited to the above-mentioned embodiments and portions may be appropriately changed as will be described below. 
     That is, in the above-mentioned embodiments, the inclined structure of the drain passages  27  as the flow guide device and the drawing structure of the drawing grooves  28  have been described as an example of the drainage function-shape portion. However, the drainage function-shape portion according to the invention is not limited to such an example, and may be of any portion as long as it is formed to have a function of discharging the water, which has been introduced into the housing case, to the outside of the housing case while including a drain hole that makes the inside and outside of the housing case  20  communicate with each other. For example, various shapes, such as those having an appropriate inclination, appropriate grooves, or appropriate steps, may be selected. Further, the drain holes  25 , which makes the inside and outside of the housing case communicate with each other as described above, may form the drainage function-shape portion according to the invention alone. 
     Second Example 
     Next, third and fourth embodiments, which are embodied in a second example shown in  FIGS. 13 to 21 , will be described. 
     Third Embodiment 
     The third embodiment, which embodies the battery pack according to the invention, will be described below with reference to  FIGS. 13 to 17 . 
       FIG. 13  shows the appearance of a battery pack  110 , which is the third embodiment embodied in the second example, in perspective.  FIG. 14  shows the battery pack  110  that is seen from above.  FIG. 15  shows the cross-section of the internal structure of the battery pack  110  taken along line XV-XV in  FIG. 14 .  FIG. 16  shows the cross-section of the internal structure of the battery pack  110  taken along line XVI-XVI in  FIG. 14 . Meanwhile, in the following description, the electrical connection side of the battery pack  110  is defined as the upper side and the slide mounting direction of the battery pack  110  is defined as a front side. 
     The battery pack  110  shown in  FIGS. 13 to 16  is adapted to be detachably mounted by sliding onto a tool body of an electric tool that is typified by, for example, an electric screwdriver. The battery pack  110  serves as a drive power source of the tool body on which the battery pack  110  has been mounted. That is, when the charge amount of the battery pack  110  is reduced, the battery pack  110  is removed from the tool body and charged by a dedicated external charger. After being completely charged by the dedicated charger, the battery pack  110  is mounted on the tool body and functions as a drive power source. Meanwhile, the battery pack  110  is adapted to be mounted (slid to be mounted) on a tool body (not shown) or a dedicated charger (not shown) by sliding when the battery pack  110  is to be mounted on the tool body or the dedicated charger. 
     As shown in  FIG. 15 , etc., the battery pack  110  generally includes a housing case  111  and an internal installation body  121 . 
     The housing case  111  has a function as an outer cover of the battery pack  110  and a function as a housing in which the internal installation body  121  is disposed. The housing case  111  includes a box-shaped case body  112  of which an upper portion is opened, and an upper cover member  116  that closes the opened upper portion of the case body  112  as an upper cover of the case body  112 . The case body  112  is configured so that the internal installation body  121  can be disposed in the box-shaped inner portion of the case body. The upper cover member  116  is mounted so as to close the opened upper portion of the case body  112  where the internal installation body  121  is disposed in the box-shaped inner portion, and is fastened by fastening screws  119  as shown in  FIGS. 13 and 14 . Accordingly, the housing case  111  is formed of a housing in which the internal installation body  121  is disposed. Meanwhile, an opening shape is formed on the housing case  111  for communicating with the inside of the housing case  111  from the outside of the housing case  111  in order to arrange electrical connection portions  134  and a male hook mechanism  140  that will be described in detail below. 
     The internal installation body  121  has a function as a power source of the battery pack  110 . That is, as shown in  FIGS. 15 and 16 , the internal installation body  121  includes a plurality of battery cells  122  and a control board  126  that is electrically connected to the plurality of battery cells  122 . The battery cells  122  are formed of battery cells, which can be charged, so that the battery pack  110  functions as a drive power source of a tool body. The plurality of battery cells  122  are disposed within the above-mentioned housing case  111 , and are electrically connected to the control board  126 . The control board  126  appropriately performs controls when the battery cells  122  are charged or discharged. Meanwhile, the control board  126  is electrically connected to a connection terminal  1361  of a positive connection portion  1341 , a connection terminal  1362  of a negative connection portion  1342 , and a connection terminal  1363  of a control connection portion  1343  that are shown in  FIG. 14  and will be described below. 
     Incidentally, a slide mounting portion  130 , which is to be mounted on a tool body (not shown) or a dedicated charger (not shown), is provided on the upper surface of the above-mentioned housing case  111 . The slide mounting portion  130  has a function of allowing the battery pack  110  to slide to be mounted on the tool body (not shown) or the dedicated charger (not shown). For this reason, the slide mounting portion  130  has a function of guiding the slide mounting of the battery pack  110 , and a function as an electrical connection portion for allowing the electrical connection with the battery pack  110  that is mounted by sliding. That is, the slide mounting portion  130  includes the slide guide portions  131  that guide the slide mounting of the battery pack  110 , and the electrical connection portions  134  that electrically connect the battery pack  110 . 
     The slide guide portions  131  are formed in male guide shapes that protrude in a left-and-right width direction in the shape of an outer flange and extend in a front and rear direction. The slide guide portions  131  can be fitted to female guide shapes, which are formed on the tool body (not shown) or the dedicated charger (not shown), in the slide direction. For this reason, the slide guide portions  131  are formed in the shapes of outer flanges, which appropriately protrude in the left-and-right width direction, so as to make a pair in the left-and-right width direction on an upper surface  117  of the battery pack  110 . Meanwhile, the front side of the battery pack  110 , which is defined in the drawings as described above, conforms to the slide mounting direction and the rear side of the battery pack  110 . The rear side of the battery pack is defined in the drawings and conforms to a removal direction. 
     The electrical connection portions  134  are provided on the rear side of the above-mentioned slide guide portions  131 . The electrical connection portions  134  are portions that are electrically connected to the connection terminals provided on the tool body when the battery pack  110  is slid to be mounted on the tool body as a mounting target. For this reason, the electrical connection portions  134  are formed of the three connection portions. That is, the positive and negative connection portions  1341  and  1342  that are connection portions for the charge or discharge of electric power, while the control connection portion  1343  is a connection portion to be connected to the above-mentioned control board  126 . 
     These three electrical connection portions  134  (the positive connection portion  1341 , the negative connection portion  1342 , and the control connection portion  1343 ) generally include terminal receiving grooves  135  and battery-side connection terminals  136 , which are individually and specifically configured as described below. Meanwhile, since the positive and negative connection portions  1341  and  1342  are symmetrically formed so as to make a pair, the positive connection portion  1341  will be described in the following description, and the same description will be applied to the negative connection portion  1342 . 
     That is, the positive connection portion  1341  (the negative connection portion  1342 ) includes a receiving groove  1351  (a receiving groove  1352 ) as the terminal receiving groove  135  and a connection terminal  1361  (a connection terminal  1362 ) as the battery-side connection terminal  136 . The receiving groove  1351  is a concave groove that extends in the front and rear direction of the battery pack  110 . For example, a tool body-side connection terminal (not shown) for supplying electric power is slid to be fitted into the receiving groove  1351 . The connection terminal  1361  is disposed in the receiving groove  1351 . The connection terminal  1361  is electrically connected to the tool body-side connection terminal (not shown) that is slid to be fitted into the concave groove of above-mentioned receiving groove  1351 . The connection terminal  1361  is formed by leaf spring-type metal terminals that are disposed so as to face each other as shown in  FIGS. 14 and 16 . 
     The control connection portion  1343  is provided between the above-mentioned positive and negative connection portions  1341  and  1342 . The control connection portion  1343  includes a receiving groove  1353  as the terminal receiving groove  135  and a connection terminal  1363  as the battery-side connection terminal  136 . The receiving groove  1353  is a concave groove extending in the front and rear direction of the battery pack  110 . For example, a tool body-side control connection terminal (not shown) is slid to be fitted into the receiving groove  1353 . Meanwhile, the length of the receiving groove  1353  is set to be shorter than the length of the receiving groove  1351  (the receiving groove  1352 ) of the above-mentioned positive connection portion  1341  (the negative connection portion  1342 ). The connection terminal  1363 , which has the same structure as the structure of the connection terminal  1361  (the connection terminal  1362 ) of the above-mentioned positive connection portion  1341  (the negative connection portion  1342 ), is disposed in the receiving groove  1353 . 
     Meanwhile, the connection terminal  1361  of the positive connection portion  1341 , the connection terminal  1362  of the negative connection portion  1342 , and the connection terminal  1363  of the control connection portion  1343  are electrically connected to the above-mentioned control board  126 . For this purpose, opening shapes, which communicate with the inside of the housing case  111  from the outside of the housing case  111  for allowing connection to the control board  126 , are formed at a portion where the connection terminal  1361  (the positive connection portion  1341 ) is arranged, an portion where the connection terminal  1362  (the negative connection portion  1342 ) is arranged, and a portion where the connection terminal  1363  (the control connection portion  1343 ) is arranged. The communicating opening shapes correspond to a communication opening according to the invention. 
     For this reason, the peripheral portion of the portion where the connection terminal  1361  (the positive connection portion  1341 ) is arranged, the peripheral portion where the connection terminal  1362  (the negative connection portion  1342 ) is arranged, and the peripheral portion where the connection terminal  1363  (the control connection portion  1343 ) is arranged are portions that correspond to the vicinity of the communication opening according to the invention. Specifically, portions on the front side of the electrical connection portions  134 , which include these connection terminals  1361 ,  1362 , and  1363 , are set as the peripheral portions of the arrangement portions of these connection terminals  1361 ,  1362 , and  1363  and are portions that correspond to the vicinity of the communication opening according to the invention. Here, portions on the front side of the electrical connection portions  134  including the connection terminals  1361 ,  1362 , and  1363  are positioned between the slide guide portions  131 . They also serve as upper surface portions of the upper cover member  116 . Additionally, they serve as the upper surface of the housing case  111 . Finally, they also serve as the upper surface  117  of the battery pack  110  as a whole. 
       FIG. 17  shows the upper surface  117  of the battery pack  110  in an enlarged version of that shown in  FIG. 16  for easy understanding of the upper surface  117  of the battery pack  110  positioned on the front side of the electrical connection portions  134  having the connection terminals  1361 ,  1362 , and  1363 . Meanwhile, the battery pack  110  shown in  FIG. 17  is shown as the upper surface  117  of the battery pack  110  when the battery pack  110  is placed on the horizontal surface. Further, in  FIG. 17 , a horizontal line is shown for the upper surface  117  for easy understanding of the inclined structure of the upper surface  117  of the battery pack  110 . 
     As shown in  FIG. 17 , the upper surface  117  of the battery pack  110  is formed to have an inclined structure (the shape of an inclined flat surface). The upper surface  117  of the battery pack  110  has the shape of a substantially flat surface, and has an angle of inclination such that it is inclined downward with respect to the battery pack  110  toward the front side of the battery pack  110 . In other words, the upper surface  117  of the battery pack  110  is formed in the shape of a flat surface that is inclined upward toward the electrical connection portions  134  positioned at the rear portion of the battery pack  110 . 
     That is, since the upper surface  117  of the battery pack  110  has an inclined structure having the shape of a flat surface that is inclined downward with respect to the battery pack  110  toward the front side of the battery pack  110 , the upper surface  117  of the battery pack  110  constitutes a water-introduction restricting portion according to the invention. That is, when water is put on the upper surface  117  of the battery pack  110  such as when water is splashed on the battery pack  110 , the water present on the upper surface  117  of the battery pack  110  does not flow toward the portions where the electrical connection portions  134  are arranged (the portion where the connection terminal  1361  of the positive connection portion  1341  is arranged, the portion where the connection terminal  1362  of the negative connection portion  1342  is arranged, and the portion where the connection terminal  1363  of the control connection portion  1343  is arranged) on the upper surface  117  of the battery pack  110  but flows toward the front side of the battery pack  110  that is opposite to the portions where the electrical connection portions  134  are arranged. In other words, water present on the upper surface  117  of the battery pack  110  flows in the direction away from the portions where the electrical connection portions  134  are arranged (the portion where the connection terminal  1361  of the positive connection portion  1341  is arranged, the portion where the connection terminal  1362  of the negative connection portion  1342  is arranged, and the portion where the connection terminal  1363  of the control connection portion  1343  is arranged), so that the introduction of water into the portions where the electrical connection portions  134  (the connection terminals  1361 ,  1362 , and  1363 ) are arranged is restricted. 
     Incidentally, as shown in  FIG. 17 , a stepped portion  137  is formed at a boundary portion between the above-mentioned electrical connection portion  134  (the positive connection portion  1341 ) and the upper surface  117  of the battery pack  110  positioned on the front side of the electrical connection portion  134  (the positive connection portion  1341 ). The stepped portion  137  is formed by making the front end portion of the electrical connection portion  134  (the positive connection portion  1341 ), which is set at the boundary portion, to have a shape protruding toward the upper side of the battery pack  110 . 
     Meanwhile, since  FIG. 17  is an enlarged view of  FIG. 16 , the stepped portion  137  formed at the front end portion of the positive connection portion  1341  as the electrical connection portions  134  has been described. However, the same stepped portions  137  as the stepped portion  137  formed at the front end portion of the positive connection portion  1341  are also formed at the respective front end portions of the negative connection portion  1342  and the control connection portion  1343  as the electrical connection portions  134 . 
     On the other hand, a male hook mechanism  140 , which is fitted to a female hook portion (not shown) formed on the tool body when the battery pack is mounted on the above-mentioned tool body (mounting target), is formed at the rear portion of the above-mentioned battery pack  110 . The male hook mechanism  140  corresponds to a male hook portion according to the invention. The male hook mechanism  140  is disposed so as to be received in a receiving space (a mechanism receiving space  118 ) that is formed between the above-mentioned housing case  111  and the internal installation body  121 . A male hook mechanism  140  disposed in the mechanism receiving space  118  will be explained below. 
     As shown in  FIGS. 15 and 16 , the male hook mechanism  140  includes a base member  141 , a male hook body  145 , and a biasing coil spring  149 . As shown in  FIG. 15 , the base member  141  is fixed to the housing case  111  by a screw member  142 , so that the base member  141  is disposed in the above-mentioned mechanism receiving space  118 . The base member  141  has a structure that isolates the above-mentioned housing case  111  and the internal installation body  121  from each other. That is, although not specifically shown, the base member  141  is formed so that substantially the entire peripheral edge of the base member comes into contact with the inner surface of the housing case  111 . Thus, since substantially the entire peripheral edge of the base member comes into contact with the housing case  111  as described above, the base member  141  may isolate the housing case  111  and the internal installation body  121  from each other. For this reason, the inside of the base member  141  is not seen in  FIG. 16  that is a cross-sectional view of the battery pack  110  of  FIG. 14  taken along line XVI-XVI. 
     The male hook body  145  is disposed between the above-mentioned base member  141  and the housing case  111 . The male hook body  145  is a member that moves up and down relative to the base member  141  and the housing case  111 . For this reason, as shown in  FIG. 15 , the male hook body  145  is formed so as to extend in the up and down direction in the housing case  111  while being bent along the upper and rear surfaces of the housing case  111 . The male hook body  145  generally includes a biasing guide portion  146 , an operation portion  147 , and a hook portion  148  in order from the lower side to the upper side shown in  FIG. 15 . 
     The biasing guide portion  146  forms the lower portion of the male hook body  145 , and comes into contact with the upper end of the biasing coil spring  149 . Further, the biasing guide portion  146  is positioned between the above-mentioned base member  141  and the housing case  111 , so that the movement of the biasing guide portion  146  in the front and rear direction and the left and right direction is restricted. For this reason, the biasing guide portion  146  has a function of guiding the movement of the male hook body  145  in the up and down direction while receiving a biasing force of the biasing coil spring  149 . In contrast, the operation portion  147  and the hook portion  148  are formed so as to be exposed to the outside. The operation portion  147  is formed in the middle portion of the male hook body  145 , and is formed in an appropriate concave shape that allows an operation finger of a user to be caught as also shown in  FIG. 13 . The operation portion  147  is adapted to be exposed to the outside through an operation portion exposure window  1111  that is formed at the rear portion of the housing case  111 . The hook portion  148  is formed at the upper end of the male hook body  145 , and is formed in the shape of a male hook protruding upward as also shown in  FIG. 13 . The hook portion  148  is adapted to be exposed to the outside through a hook portion exposure window  1112  that is formed at the upper portion of the housing case  111 . The hook portion  148  is formed in the shape of a male hook having an appropriate tapered shape so as to be capable of being fitted to a female hook portion (not shown), which is provided on the tool body or the dedicated charger, according to the slide mounting of the battery pack  110 . 
     For this purpose, the operation portion exposure window  1111  and the hook portion exposure window  1112 , which have shapes of openings communicating with the inside of the housing case  111  from the outside of the housing case  111 , are formed at the housing case  111  in order to expose the above-mentioned operation portion  147  and the hook portion  148  to the outside. Specifically, the operation portion exposure window  1111  is formed at the rear portion of the housing case  111  so that the above-mentioned operation portion  147  can be operated up and down. Specifically, as shown in  FIGS. 13 and 14 , the operation portion exposure window  1111  is formed in the shape of a rectangular opening that communicates with the inside of the housing case  111  from the outside of the housing case  111 . Further, as shown in  FIGS. 13 and 14 , the hook portion exposure window  1112  is formed at the upper portion of the housing case  111  so that the above-mentioned hook portion  148  can protrude from and retreat into the hook portion exposure window  1112 . The hook portion exposure window  1112  is formed in the shape of a U-shaped opening that communicates with the inside of the housing case  111  from the outside of the housing case  111 . Here, the operation portion exposure window  1111  and the hook portion exposure window  1112 , which have the shapes of communication openings, correspond to the communication opening according to the invention. For this reason, the peripheral portions of the arrangement portions of the operation portion exposure window  1111  and the hook portion exposure window  1112  correspond to the vicinity of the communication opening according to the invention. 
     The biasing coil spring  149  is a coil spring that is widely used. The lower end of the biasing coil spring  149  comes into contact with the inner surface of the base member  141 , and the upper end of the biasing coil spring  149  comes into contact with the lower portion of the male hook body  145 . Accordingly, the biasing coil spring  149  biases the male hook body  145  upward. In this way, the male hook mechanism  140  in the normal state urges the hook portion  148  of the male hook body  145  to protrude from the hook portion exposure window  1112  by the biasing force of the biasing coil spring  149 . That is, the hook portion can be fitted to a female hook portion (not shown) that is provided on the tool body. On the other hand, when the operation portion  147  exposed to the outside through the operation portion exposure window  1111  is moved downward against the biasing force of the biasing coil spring  149 , the hook portion  148  of the male hook body  145  protruding from the hook portion exposure window  1112  retreats. That is, it is possible to release the fitting between the hook portion  148  and the female hook portion (not shown). 
     Here, a stepped guide portion  150  is provided on the housing case  111  at a position on the upper side of the portion where the operation portion exposure window  1111  is arranged. The stepped guide portion  150  is formed in a convex shape that separates the water, which is present at the peripheral portion of the arrangement portion of the hook portion exposure window  1112 , from the hook portion exposure window  1112 . As shown in  FIGS. 13 and 14 , the stepped guide portion  150  is formed so that the water, which is present on the outer surface of the housing case  111 , flows along the outer surface of the housing case  111  without reaching the hook portion exposure window  1112 . Specifically, as shown in  FIGS. 13 and 14 , a stepped portion protruding outward in a shape of a mountain with its upper side being convex, is formed at the stepped guide portion  150 . The mountain-shaped stepped portion of the stepped guide portion  150  is formed so that a mountain-shaped peak portion (reference numeral  151 ) is positioned above the portion where the operation portion exposure window  1111  is arranged and both mountain-shaped bases (reference numeral  152 ) are positioned on both left and right sides of the portion where the operation portion exposure window  1111  is arranged. Meanwhile, the protruding height of the stepped guide portion  150 , which is a difference in level, is set so as to be reduced from the mountain-shaped peak portion (reference numeral  151 ) toward both the mountain-shaped bases (reference numeral  152 ). The mountain-shaped stepped portion of the stepped guide portion  150  forms the water-introduction restricting portion according to the invention. That is, the stepped guide portion  150  guides the movement of water so as to restrict the introduction of water into the operation portion exposure window  1111  when water is splashed on the battery pack  110  or the like. 
     Meanwhile, since the above-mentioned base member  141  is configured so as to have a structure for isolating the housing case  111  and the internal installation body  121  from each other, it is possible to restrict the intrusion of the water, which is introduced into the housing case  111 , into the internal installation body  121  by the base member  141  even in the case that water has been introduced into the housing case  111  from the operation portion exposure window  1111  and the hook portion exposure window  1112 . 
     According to the above-mentioned battery pack  110 , it is possible to obtain the following functions and effects. 
     That is, according to the above-mentioned battery pack  110 , opening shapes are formed in order to arrange the electrical connection portions  134  and the male hook mechanism  140 . Here, the stepped guide portion  150  and the upper surface  117  of the above-mentioned battery pack  110  as the water-introduction restricting portion, which is provided on the housing case  111 , act so as to restrict the introduction of the water, which is splashed from the outside, into the opening shapes. Accordingly, it is possible to improve the waterproof property of the battery pack  110  by restricting the intrusion of water into the housing case  111  from the outside of the housing case  111 . 
     Further, according to the above-mentioned battery pack  110 , the inclined structure of the upper surface  117  of the battery pack  110  is provided on the front side of the portions where the battery-side connection terminals  136  (the connection terminal  1361  of the positive connection portion  1341 , the connection terminal  1362  of the negative connection portion  1342 , and the connection terminal  1363  of the control connection portion  1343 ) are arranged. Accordingly, it is possible to make the water, which is present in the periphery of the portions where the battery-side connection terminals  136  are arranged, to flow in the direction away from the portions where the battery-side connection terminals  136  are arranged, by the inclined structure. Therefore, since it is possible to separate the water, which is present on the upper surface  117  of the battery pack  110 , from the portions where the battery-side connection terminals  136  are arranged, it is possible to improve the waterproof property of the battery pack  110  by restricting the introduction of water into the housing case  111  from the outside of the housing case  111 . Accordingly, it is possible to make the contact between water such as raindrops and the battery-side connection terminals  136  more difficult. 
     Furthermore, according to the above-mentioned battery pack  110 , since the water-introduction restricting portion is formed in the uneven shape that isolates the water, which is present in the vicinity of the communication opening, from the communication opening, it is possible to separate the water, which is present in the vicinity of the communication opening, from the communication opening. Accordingly, it is possible to restrict the introduction of water into the housing case  111  from the outside of the housing case  111  by separating water from the communication opening, so that it is possible to improve the waterproof property of the battery pack  110 . 
     Moreover, according to the above-mentioned battery pack  110 , the stepped guide portion  150  is provided on the housing case  111  on the upper side of the operation portion exposure window  1111 , which is a portion where the male hook mechanism  140  as a male hook portion is arranged. Due to the stepped convex shape of the stepped guide portion  150 , it is possible to isolate the water, which is present in the periphery of the operation portion exposure window  1111 , from the operation portion exposure window  1111 . Accordingly, it is possible to restrict the introduction of water into the housing case  111  from the outside of the housing case  111  by isolating water from the operation portion exposure window  1111 , so that it is possible to improve the waterproof property of the battery pack  110 . 
     Further, according to the above-mentioned battery pack  110 , the stepped portions  137  are formed at the boundary portions between the electrical connection portions  134  (the positive connection portion  1341 , the negative connection portion  1342 , and the control connection portion  1343 ) and the upper surface  117  of the battery pack  110  positioned on the front side of the electrical connection portions  134 . Accordingly, due to the stepped convex shape, it is possible to isolate the water, which is present in the periphery of the electrical connection portions  134 , from the electrical connection portions  134 . Therefore, it is possible to restrict the introduction of water into the housing case  111  from the outside of the housing case  111  by isolating water from the electrical connection portions  134 , so that it is possible to improve the waterproof property of the battery pack  110 . 
     Fourth Embodiment 
     Next, the fourth embodiment, which embodies the battery pack according to the invention, will be described with reference to  FIG. 18  and its subsequent figures. Meanwhile, a battery pack  160  of the fourth embodiment is an embodiment where vent holes  171  and  181  are formed in the structure of the battery pack  110  of the above-mentioned third embodiment. That is, the battery pack  160  of the fourth embodiment has substantially the same structure as the structure of the battery pack  110  of the third embodiment. For this reason, the same portions of the battery pack  160  of the fourth embodiment as the portions of the battery pack  110  of the above-mentioned third embodiment are denoted by the reference numerals having been used in the description of the battery pack  110  of the third embodiment, and the description thereof will be omitted. Meanwhile, the structure of a male hook mechanism  140 A of the battery pack  160  of the fourth embodiment is slightly different from that of the male hook mechanism  140  of the battery pack  110  of the third embodiment. That is, the male hook mechanism  140 A of the fourth embodiment is different from the male hook mechanism  140  of the third embodiment in terms of the structure of the biasing coil spring  149 , and other structures of the fourth embodiment are the same as those of the third embodiment. For this reason, portions of the male hook mechanism  140 A of the fourth embodiment are denoted by reference numerals having “A” at the ends thereof, and the description thereof will be omitted. 
       FIG. 18  shows the appearance of the battery pack  160 , which is the fourth embodiment, in perspective.  FIG. 19  shows the battery pack  160  that is seen from above.  FIG. 20  shows the cross-section of the internal structure of the battery pack  160  taken along line XX-XX in  FIG. 19 .  FIG. 21  shows the cross-section of the internal structure of the battery pack  160  taken along line XXI-XXI in  FIG. 19 . Meanwhile, in the following description, the electrical connection side of the battery pack  160  is defined as the upper side and the slide mounting direction of the battery pack  160  is defined as a front side. 
     Two vent holes  171  and  181  having appropriate opening shapes are formed in an upper surface  161  of the battery pack  160  shown in  FIGS. 18 to 21 . That is, reference numeral  171  denotes an intake-side vent hole. The intake-side vent hole  171  is adapted to send cooling air, which has been sent from a dedicated charger or the like, toward an internal installation body  121  that is disposed in a housing case  111 . Further, reference numeral  181  denotes an exhaust-side vent hole. The exhaust-side vent hole  181  is adapted to discharge the cooling air that has been sent to the internal installation body  121  and passed through the internal installation body  121 . These vent holes  171  and  181  allow the temperature of the internal installation body  121  (battery cells  122  and a control board  126 ) to be lowered by cooling air and allow the time, which is required until the battery pack  160  is fully charged, to be shortened. In detail, during charging the battery pack  160  by a dedicated charger, the temperature of the internal installation body  121  (the battery cells  122  and the control board  126 ) rises due to the charge of the battery pack  160 . However, since the temperature of the internal installation body  121  can be lowered by the cooling air sent from the vent holes  171  and  181 , a charge effect is improved. As a result, the time, which is required until the battery pack  160  is fully charged, is shortened. That is, the cooling air, which is sent from a dedicated charger or the like, is introduced into the housing case  111  from the intake-side vent hole  171 , cools the internal installation body  121 , and is discharged to the outside of the housing case  111  from the exhaust-side vent hole  181 . Meanwhile, the exhaust-side vent hole  181  is formed in a shape that is merely opened, unlike the intake-side vent hole  171  that will be described in detail below. 
     As shown in  FIGS. 18 to 21 , the two vent holes  171  and  181  are formed on the upper surface  161  of the battery pack  160  at two portions, that is, rear and front portions of the battery pack  160 . That is, the intake-side vent hole  171  is formed at the rear portion of the upper surface  161  of the battery pack  160 . The intake-side vent hole  171  is formed on the upper surface  161  of the battery pack  160  that is present between the male hook mechanism  140 A and the electrical connection portions  134  (a positive connection portion  1341 , a negative connection portion  1342 , and a control connection portion  1343 ). As also shown in  FIG. 18 , the intake-side vent hole  171  is formed in a shape of an opening in the upper surface  161  of the battery pack  160  so that air can be introduced into the housing case  111  from the outside of the housing case  111 . For this reason, the intake-side vent hole  171  corresponds to the communication opening according to the invention. Further, the periphery of the portion where the intake-side vent hole  171  is arranged corresponds to the vicinity of the communication opening according to the invention. Specifically, a peripheral edge  172  of the intake-side vent hole  171  and a periphery  173  of the peripheral edge  172  are set as the periphery of the portion where the intake-side vent hole  171  is arranged. Here, a first convex rib  175 , which protrudes upward, is formed at the peripheral edge  172  of the intake-side vent hole  171 . The first convex rib  175  protrudes upward so as to be higher than the periphery  173  of the intake-side vent hole  171  that forms the upper surfaces of the electrical connection portions  134 . For this reason, due to the convex shape of the first convex rib  175 , it is possible to isolate the water, which is present in the periphery  173  of the portion where the intake-side vent hole  171  is arranged, from the portion where the intake-side vent hole  171  is arranged. Accordingly, it is possible to improve the waterproof property of the battery pack  160  by restricting the intrusion of water into the housing case  111  from the intake-side vent hole  171 . 
     Moreover, second convex ribs  177  are formed at the boundary portions between the periphery  173  of the portion where the above-mentioned intake-side vent hole  171  is arranged and the above-mentioned electrical connection portions  134  (the positive connection portion  1341 , the negative connection portion  1342 , and the control connection portion  1343 ). Like the above-mentioned first convex rib  175 , the second convex ribs  177  protrude upward so as to be higher than the periphery  173  of the intake-side vent hole  171  that forms the upper surfaces of the electrical connection portions  134 . For this reason, due to the convex shape of the second convex ribs  177 , it is possible to isolate the water, which is present in the vicinity  173  of the portions where the electrical connection portions  134  are arranged, from the portions where the electrical connection portions  134  are arranged. Accordingly, it is possible to improve the waterproof property of the battery pack  160  by restricting the intrusion of water into the housing case  111  from the electrical connection portions  134 . 
     Meanwhile, the battery pack according to the invention is not limited to the above-mentioned embodiments, and appropriate portions of the battery pack may be modified as described below. 
     That is, the electrical connection portions  134  (the positive connection portion  1341 , the negative connection portion  1342 , and the control connection portion  1343 ), the operation portion exposure window  1111 , the hook portion exposure window  1112 , and the intake-side vent hole  171  have been exemplified as the communication opening of the above-mentioned embodiment. However, the communication opening according to the invention is not limited to the above-mentioned embodiment, and any construction allowing communication with the inside of the housing case from the outside of the housing case may correspond to the communication opening according to the invention. Further, the water-introduction regulating portion according to the invention is also not limited to the above-mentioned embodiment, and any construction restricting the introduction of the water, which is present in the vicinity of the communication opening, into the communication opening may correspond to the water-introduction regulating portion according to the invention. That is, the water-introduction regulating portion according to the invention may be the inclined structure that makes the water, which is present in the vicinity of the communication opening, flow in the direction away from the communication opening. Alternatively, it can be any structure that is formed in an uneven shape for isolating water present in the vicinity of the communication opening from the communication opening. Furthermore, the “uneven shape” is not limited to, for example, the above-mentioned convex ribs  175  and  177  having the shape of protrusions, but may include a convex wall structure having convex ribs, a concave groove structure, and/or an appropriate uneven step shaped structure. 
     Meanwhile, the battery pack  160  of the above-mentioned fourth embodiment may be positively provided with a water release passage as will be described below. That is, the periphery  173  of the portion where the intake-side vent hole  171  is arranged is isolated due to the convex shapes of the above-mentioned first and second convex ribs  175  and  177 , and therefore, water is apt to be collected due to these convex shapes. For this reason, a water release passage may be formed to allow release of water collected in the vicinity  173  of the portion where the intake-side vent hole  171  is arranged due to these convex shapes escapes. A structure having an appropriate shape may be proposed as the water release passage, but, for example, the following structure may be used as the water release passage. That is, the hook clearance  179  formed between the hook portion exposure window  1112  and the hook portion  148 A of the male hook body  145 A described in the above-mentioned third embodiment may be configured as an inlet of the water release passage, and the above-mentioned operation portion exposure window  1111  may be configured as an outlet of the water release passage. If the hook clearance  179  is configured as the inlet of the water release passage as described above, water is temporarily introduced into the housing case  111 , flows along the base member  141 A, and is discharged to the outside of the housing case  111  from the operation portion exposure window  1111 . Meanwhile, since the base member  141 A isolates the housing case  111  and the internal installation body  121  from each other as described above, water that has been temporarily introduced into the housing case  111  may not reach the internal installation body  121 . That is, it is possible to allow water to flow along the base member  141 A and to be discharged to the outside of the housing case  111  from the operation portion exposure window  1111 . Meanwhile, other than using the operation portion exposure window  1111 , the outlet of the water release passage may be appropriately formed. For example, a case communication hole, which is formed at the housing case  111  near the lower end of the base member  141 A and communicates the inside of the housing case  111  with the outside of the housing case  111  in a vertical direction, may be formed as the outlet of the water release passage. If the outlet of the water release passage is formed to allow for communication between the inside of the housing case  111  and the outside of the housing case  111  in the vertical direction as described above, water is easily discharged to the outside of the housing case  111  from the lower portion of the housing case  111 . 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
         
           
               10 ,  10 A: battery pack 
               20 : housing case 
               201 : support lower surface 
               21 ,  21 B: case body 
               211 : bottom wall portion 
               212 : side wall portion 
               221 : outer surface 
               222 : inner surface 
               223 : bottom surface 
               23 : rib 
               231 : support rib 
               232 : air guide rib 
               233 : foreign material-introduction restricting rib 
               25 ,  25 A,  25 B: drain hole (drainage function-shape portion) 
               261 : outer end edge 
               262 : inner end edge 
               27 ,  27 B: drain passage (drainage function-shape portion, flow guide means) 
               28 : drawing groove (drainage function-shape portion, draw guide means) 
               31 : upper cover member 
               32 : slide guide portion 
               33 : connection opening 
               34 : hook-exposure opening 
               35 : air vent opening 
               39 : screw member 
               40 : battery pack body 
               41 : battery cell 
               42 : electrode 
               45 : lead plate 
               46  ( 461 ,  462 ,  463 ): left lead plate 
               47  ( 471 ,  472 ,  473 ): right lead plate 
               51 : connection control board 
               52 : control board 
               53 : connection terminal portion 
               55 : male hook mechanism 
               56 : hook-type structure 
             C: clearance 
             F: placement surface