Patent Publication Number: US-2020303692-A1

Title: Battery pack

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This is a continuation application of U.S. patent application Ser. No. 15/842,931, filed Dec. 15, 2017, which is a continuation of U.S. patent application Ser. No. 14/692,407, filed Apr. 21, 2015, now U.S. Pat. No. 9,882,186, which is a continuation of U.S. patent application Ser. No. 12/041,376, filed Mar. 3, 2008, now U.S. Pat. No. 9,040,195, which contains subject matter related to Japanese Patent Application JP 2007-095323, Japanese Patent Application JP 2007-095331, Japanese Patent Application JP 2007-095327, Japanese Patent Application JP 2007-095321, Japanese Patent Application JP 2007-095322, and Japanese Patent Application JP 2007-095324 which are filed in the Japan Patent Office on Mar. 30, 2007, the entire contents of which being incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a battery pack which is formed so that it can be attached to and detached from an electronic apparatus and in which battery cells for supplying driving electric power to the apparatus main body is contained. 
     2. Description of the Related Art 
     As portable electronic apparatuses such as digital still cameras and camcorders, there have widely been used those which are provided with a battery mounting portion such that a battery pack loaded with battery cells is attached thereto and detached therefrom by the user himself. At the time of using such an apparatus, a previously charged battery pack is attached to the battery mounting portion, and, when the battery has run down, the battery is replaced with a separately charged spare battery pack, whereby the apparatus can be used for a long time. 
     In addition, the lithium ion secondary batteries used for portable electronic apparatuses in recent years include those for which the smart battery specification is adopted as a specification for specifying the management of data between the electronic apparatus and the battery pack and the charger and which include data communication terminals conforming to the SMBus (System Management Bus) communication protocol, in addition to positive and negative electrode terminals. In this kind of battery pack, a smart battery standard IC is mounted, and the residual battery capacity, i.e., how long the battery can be used more, is computed based on such data as temperature characteristics, cycle characteristics, etc. of battery cells incorporated in the battery pack and the environment and history of use of the battery pack, and is communicated to the electronic apparatus side. Further, in order to cope with pirated products, there has been proposed a system in which ID information indicating that the battery pack mounted in position is a genuine product and the like are transmitted to the electronic apparatus, and the battery in question is accepted on the electronic apparatus side only when the battery pack is certified as a genuine product. 
     It is convenient to arrange such communication terminals side by side with the electrode terminals at a face of the battery pack, from the viewpoints of attachment and detachment of the battery pack to and from the battery mounting portion as well as the configurations of the battery pack and the battery mounting portion. However, where the communication terminals are arranged side by side with the electrode terminals, electromagnetic radiation from the electrode terminals or electrode tabs connected to the battery cells may influence heavily or hamper the accurate data communication. 
     Each of this kind of battery packs is provided with terminal portions corresponding to electrode terminals disposed on the battery mounting portion side, and is attached to the battery mounting portion in such a manner that the terminal portions are mated to the electrode terminals. Here, in business-use camcorder and the like, the battery capacity required is higher, the battery cells incorporated therein are hence larger and the battery pack is larger in size and weight, since the use time is longer and the use frequency is higher, as compared with private-use camcorders and the like. In the business-use camcorders and the like, therefore, the loads exerted on the engaging members provided between the battery pack and the battery mounting portion to which the battery pack is attached have been increasing, and, when vibration is generated on the apparatus main body side during use, excessive loads would be exerted on the engaging members. Therefore, the engaging members formed in the battery mounting portion and the battery pack are enlarged in size in order to be enhanced in strength. 
     Meanwhile, of the battery packs, those ones in which lithium ion batteries are used have, incorporated therein, a circuit board including a protective circuit for stopping charging upon overcharge, for stopping discharging upon over-discharge, for stopping a large-current discharge such as an external short-circuit and for the like purposes. When an engaging portion formed in a battery pack is enlarged in size, the engaging portion protrudes largely to the inner side, so that the circuit board disposing region would be narrowed, restrictions would be imposed on mounting regions or patterning regions for circuit elements, and the degree of freedom in designing the circuit board would be spoiled. In addition, if the circuit board is disposed while avoiding the engaging portion, the battery pack would be enlarged in size accordingly, and a dead space would be generated between the circuit board and the battery pack. 
     Further, this kind of battery pack is provided at one surface thereof with terminal portions to be joined to electrode terminals formed at a battery mounting portion of an electronic apparatus. Electrode tabs which are connected to battery cells contained in the battery pack and electrode members which are connected to the electrode tabs and to which the electrode terminals on the battery mounting portion side are joined, are disposed at the terminal portions. The electrode member includes a terminal plate, a metallic bearing or the like according to the shape of the electrode terminal on the battery mounting portion side. In the battery pack, the one surface is provided with a recessed surface portion, and end faces of the electrode members are exposed from a bottom surface of the recessed surface portion, whereby the electrode members are prevented from short-circuiting or being broken. 
     However, disposing the electrode members at the bottom surface of the recessed surface portion has been found unsatisfactory for preventing the electrode members from short-circuiting or being broken. Besides, in the case where the electrode member is configured as a metallic bearing, the insertion of terminal pins constituting the electrode terminals on the battery mounting portion side into opening ends of the metallic bearings exposed from the bottom surface of the recessed surface portion could not be smoothly carried out, due to interference of the terminal pins with the bottom surface or the like. 
     Still further, if the residual capacities of batteries can be checked at the time of loading or replacing a battery pack, it is possible to select a spare battery pack with more residual capacity from among a plurality of spare battery packs and to discriminate the spare battery pack with more residual capacity from already exhausted battery packs, which is convenient. However, where there are a plurality of spare battery packs, it is time consuming to confirm the residual capacities of the battery packs one by one. Therefore, it has been desired that the residual capacities of a plurality of spare battery packs can be checked collectively, in the case where speedy battery replacement is necessary, such as during shooting. 
     In addition, a battery pack of the type in which the residual battery capacity is displayed with light emitting elements turned ON has the problem that the visibility of the residual battery capacity display would be lowered outdoors in a fine weather or in a light-illuminated place. On the other hand, a residual capacity display method in which the light emitting elements are normally turned ON at a high luminance consumes a considerable amount of electric power and is uneconomic. 
     Still further, this type of battery packs are each provided with terminal portions corresponding to electrode terminals disposed on the battery mounting portion side, and need to be mounted to the battery mounting portion so that the electrode terminals are mated with the terminal portions. In this kind of electronic apparatuses, therefore, various mechanisms for preventing mis-mounting of battery pack are adopted, such as a mechanism in which the battery pack cannot be inserted into the battery mounting portion if the battery pack is about to be inserted in a wrong mounting direction and a mechanism in which the battery pack cannot be inserted to the depth of the battery mounting portion in such a situation. 
     However, all of these methods have problems as follows. Whether or not the mounting direction is right cannot be judged unless it is once tried to insert the battery pack into the battery mounting portion. Therefore, in order to mount the battery pack correctly, it would be necessary to visually check the orientation of the battery pack before mounting. 
     However, in the case where replacement of battery pack is necessary during use of a digital still camera or a camcorder, there is often little time to visually confirm the orientation of the battery pack. Besides, the electronic apparatus is not necessarily used in a light place, and it may be difficult to visually check the orientation of the battery pack in relation to the battery mounting portion. 
     Meanwhile, it is convenient that the loading/unloading direction of the one surface provided with the terminal portions in relation to the surface provided with the electrode terminals on the battery mounting portion side can be judged intuitively without needing visual confirmation. In general, however, this kind of battery pack is substantially rectangular in shape, and the electrode terminals are not exposed to the outside, so that it is difficult, by relying on the outside shape only, to check the loading/unloading direction of the battery pack in relation to the battery mounting portion. 
     Furthermore, in business-use camcorders and the like, the use time is longer and the use frequency is higher, so that the battery capacity required would be higher, as compared with private-use camcorders and the like. Accordingly, the battery packs for business-use camcorders and the like are enlarged in size and weight, which may lead to accidental dropping of the battery pack at the time of replacement thereof. 
     Still further, each of this kind of battery packs is provided with terminal portions corresponding to electrode terminals disposed on the battery mounting portion side, and is attached to the battery mounting portion in such a manner that the terminal portions are mated to the electrode terminals. Here, in business-use camcorders and the like, the battery capacity required is higher and the battery pack is hence larger in size and weight, since the use time is longer and the use frequency is higher, as compared with private-use camcorders and the like. In the business-use camcorders and the like, therefore, if chattering is present between the battery pack and the battery mounting portion to which the battery pack is mounted, the loads exerted on the battery pack and the battery mounting portion due to vibrations on the apparatus main body side during use would be high. 
     On the other hand, in the case where a recess shape for contriving engagement with a protrusion shape projectingly provided at the battery mounting portion is formed in a large size in a mount surface, for mounting to the battery mounting portion, of the battery pack in order to prevent the chattering, the identification label adhering region of the mount surface would be narrowed, and the size of the circuit board disposed on the inner surface side of the mount surface and an electronic part mounting region would be limited. 
     [Patent Document 1]
     Japanese Patent Laid-open No. Hei 9-243718   

     [Patent Document 2]
     Japanese Patent Application No. Hei 10-144195   

     [Patent Document 3]
     Japanese Patent Laid-open No. Hei 10-312782   

     [Patent Document 4]
     Japanese Patent Laid-open No. Hei 5-101852   

     [Patent Document 5]
     Japanese Patent Laid-open No. 2002-124223   

     [Patent Document 6]
     Japanese Patent Laid-open No. 2006-228471   

     SUMMARY OF THE INVENTION 
     Thus, there is a need for a battery pack which includes electrode terminals and data communication terminals and with which accurate data communication can be achieved through suppressing the influence of the terminal electrodes. 
     According to one embodiment of the present invention, there is provided a battery pack including first to fifth terminal portions sequentially arrayed at one side surface of a housing, wherein of the terminal portions, the first terminal portion formed on one end side of the one side surface is a positive electrode terminal, the fifth terminal portion formed on the other end side of the one side surface is a negative electrode terminal, the fourth terminal portion formed adjacently to the fifth terminal portion is an ID terminal for identification of the battery pack, and the fourth terminal portion and the fifth terminal portion are proximate to each other; and a guide portion for guiding the loading and unloading of the battery pack into and from a battery mounting portion is formed substantially in the center of the one side surface in array with the terminal portions, and the third terminal portion arranged centrally is formed at a position deviated toward the one end side or the other end side. 
     According to another embodiment of the present invention, there is provided a battery pack including a battery cell, and a circuit board provided with at least a protective circuit for said battery cell, the battery cell and the circuit board being contained in a housing, and the battery pack being loaded and unloaded by sliding the housing in a battery mounting portion, wherein the housing is provided with a lock recess for engagement with a lock protrusion formed to protrude from a battery mounting portion on the electronic apparatus side, the lock recess provided in one or each of side surfaces adjacent to a mount surface for mounting to the battery mounting portion through a side edge parallel to the sliding direction of the mount surface; and the lock recess includes an inclined surface portion for drawing in the lock protrusion, a clamped portion to be clamped between a bottom surface of the battery mounting portion and the lock protrusion, and an orthogonal surface portion continuous with the inclined surface portion and extended in a height direction substantially orthogonal to the mount surface. 
     According to a further embodiment of the present invention, there is provided a battery pack including a terminal portion including a terminal hole which is formed in one surface of a battery case and in which a terminal pin is inserted, and a metallic bearing which is disposed in continuity with the terminal hole and which is connected to the terminal pin inserted into the battery case through the terminal hole, wherein the terminal hole includes a recessed surface portion which is formed in the one surface and which is provided in its bottom surface with an insertion hole for inserting the terminal pin therein, and a guide portion which is formed in an insertion hole formed in the recessed surface portion and which guides the terminal pin to the metallic bearing; and the metallic bearing is formed to be approximately equal in diameter to the guide portion and disposed to be continuous with the guide portion. 
     According to yet another embodiment of the present invention, there is provided a battery pack including: a display unit configured to display the residual capacity of a battery; a residual capacity display switch configured to turn on the display unit; detecting means for detecting a depressed state of the residual capacity display switch; and control means for changing over the display condition of the display unit according to the time for which the residual capacity display switch is depressed. 
     According to a yet further embodiment of the present invention, there is provided a battery pack which has a roughly rectangular shape and in which a battery cell is contained, wherein an identification portion is formed at a grip surface which is adjacent to one surface where a terminal portion for connection with a terminal provided on the battery mounting portion side fronts and to another surface opposite to the one surface and which is gripped at the time of loading and unloading the battery pack to and from the battery mounting portion, the identification portion being formed along the direction of loading and unloading the battery pack to and from the battery mounting portion. 
     According to still another embodiment of the present invention, there is provided a battery pack loaded and unloaded to and from a battery mounting portion while sliding one surface thereof, wherein the one surface is provided with an insertion guide groove along the sliding direction; and the insertion guide groove is provided with a guide groove portion in which a protrusion protruding from the battery mounting portion is inserted, and a lock recess which is continuous with one end on the rear end side, in the direction of mounting to the battery mounting portion, of the guide groove portion, which is larger in width than the guide groove portion and which has a lock wall for locking a lock member provided in the battery mounting portion. 
     In accordance with the present invention, especially the one embodiment of the invention, the fourth terminal portion constituting an ID terminal is disposed proximate to the fifth terminal portion constituting the negative electrode terminal, so that the distance between the ID detecting device and the negative electrode line can be designed to be short, making it possible to perform accurate ID detection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are perspective views of a large size battery; 
         FIG. 2  is an exploded perspective view of the battery; 
         FIGS. 3A and 3B  are perspective views of a small size battery; 
         FIG. 4  is a side view of a camcorder in which a battery is to be mounted; 
         FIG. 5  is a perspective view of the camcorder with the battery mounted therein; 
         FIGS. 6A and 6B  are bottom views each showing the bottom surface of a housing, wherein  FIG. 6A  shows the large size battery, while  FIG. 6B  shows the small size battery; 
         FIG. 7  is a sectional view showing a circuit board disposed inside the housing; 
         FIG. 8  is a perspective view showing a battery mounting portion; 
         FIG. 9  is a perspective view showing a battery to be attached to the battery mounting portion; 
         FIGS. 10A and 10B  are side views showing a detection recess and a lock recess, respectively; 
         FIGS. 11A and 11B  each show a side view of the housing in the case where a battery of a wrong size is erroneously inserted into the battery mounting portion; 
         FIG. 12  is a perspective view showing terminal portions in a partly cut state; 
         FIG. 13  is a perspective view showing the terminal portion in a partly cut state; 
         FIG. 14  is a perspective view showing the manner in which a terminal case connected to battery cells and the circuit board is contained in a lower case; 
         FIG. 15  is a perspective view of the terminal portions formed in the housing, as viewed from inside; 
         FIG. 16  is a front view of the terminal portions; 
         FIGS. 17A and 17B  show a terminal case connected to the battery cells and the circuit board, wherein  FIG. 17A  is a front view, and  FIG. 17B  is a bottom view; 
         FIG. 18  is an exploded perspective view of a battery containing portion; 
         FIG. 19  is a perspective view of the battery containing portion; 
         FIGS. 20A and 20B  are perspective views of a terminal plate, wherein  FIG. 20A  shows a one surface side, and  FIG. 20B  shows the bottom surface side; 
         FIG. 21  is a perspective view of a containing case; 
         FIG. 22  is a perspective view of a support plate; 
         FIG. 23  is a block diagram of a residual capacity display portion; 
         FIG. 24  is a table showing the ON/OFF conditions of the residual capacity display portion; and 
         FIG. 25  is a flow chart showing the flow of display in the residual capacity display portion. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, a battery pack based on embodiments according to the present invention will be described in detail below, referring to the drawings. As shown in  FIGS. 1A and 1B , the battery pack  1  has a housing  2  containing battery cells therein and formed in a substantially rectangular shape, with terminal holes in a front surface thereof. As shown in  FIG. 2 , the housing  2  has an upper cover  3  and a lower case  4  abuttingly coupled to each other, and a plurality of battery cells  8  composed of lithium ion secondary batteries and a circuit board  9  on which a protective circuit, an SMBus (System Management Bus) controller, an ID resistor and the like are mounted and which is provided with an SMBus line are contained in the housing  2 . Besides, as shown in  FIGS. 1A, 1B, 3A and 3B , the battery packs  1  are prepared in two kinds, namely, for example, large size battery packs  1   a  and small size battery packs  1   b  made to be different from each other in electric capacity according to the number of the battery cells  8  to be contained in the housing  2 , and the two kinds of the battery packs  1  are used selectively according to the electronic apparatus for which they are used. Specifically, the large size battery pack  1   a  contains eight battery cells in two rows and four layers, while the small size battery pack  1   b  contains four battery cells in two rows and two layers. 
     Of the housing  2  thus containing the battery cells, a lower surface  2   a  is made to be a mount surface which is mounted on a battery mounting portion  5  on the electronic apparatus side, and first to fifth terminal portions  6   a  to  6   e  are disposed fronting on a front surface  2   b  which is continuous with the mount surface. Terminals formed at the terminal portions  6   a  to  6   e  have respectively predetermined functions; more specifically, the first terminal portion  6   a  is a positive electrode terminal of the battery pack  1 , the second terminal portion  6   b  is a clock line terminal in the SMBus line, the third terminal portion  6   c  is a data line terminal in the SMBus line, the fourth terminal portion  6   d  is an ID terminal connected with an ID resistor, and the fifth terminal portion  6   e  is a negative electrode terminal of the battery pack  1 . 
     In mounting the battery pack  1  in the electronic apparatus, it is inserted into the battery mounting portion  5  on the electronic apparatus side, with the lower surface  2   a  as an insertion end, and, after the lower surface  2   a  comes into abutment on a bottom surface  5   a  of the battery mounting portion  5 , the battery pack  1  is slid toward the side of the front surface  2   b , whereby lock recesses  55  and  56  provided in both side surfaces  2   c  and  2   d  of the housing  2  are locked by lock protrusions  70  formed in the battery mounting portion  5 , resulting in that the battery pack  1  is mounted in the electronic apparatus. To detach the battery pack  1  from the electronic apparatus, the battery pack  1  is slid toward the side of a back surface  2   e  opposite to the front surface  2   b  of the housing  2 , and then the battery pack  1  is pulled up toward the side of an upper surface  2   f  opposite to the lower surface  2   a , whereby the battery pack  1  is detached. 
     Examples of the electronic apparatus for which the battery pack  1  is used include a camcorder  7  shown in  FIG. 4 . The camcorder  7  is one for business use, and is provided with the battery mounting portion  5  at a back surface  7   a  of a main body thereof. The battery mounting portion  5  is so set that only the large size battery pack  1   a  having a considerable battery capacity can be mounted therein, in view of the use time and frequency of the business-use camcorder  7  and the like factors. 
     As shown in  FIG. 5 , the battery pack  1  is inserted into the battery mounting portion  5  of the camcorder  7  in the direction of an arrow D in the figure along the right side of a back surface  7   a  of the camcorder  7 , with its lower surface  2   a  as an insertion end, until it comes to a loading/unloading position where the lower surface  2   a  abuts on the bottom surface  5   a  of the battery mounting portion  5 . Next, the battery pack  1  inserted to the loading/unloading position inside the battery mounting portion  5  is slid in the direction of an arrow S, namely, leftwards in  FIG. 5 , until it comes to a mounting position where terminal pins  101  fronting on the inside of the battery mounting portion  5  are inserted in the terminal portions  6  provided at the front surface  2   b  of the battery pack  1  and, simultaneously, the lock recesses  55  and  56  provided in both side surfaces  2   c  and  2   d  of the battery pack  1  are locked by the lock protrusions  70 , whereby the mounting is completed. 
     Incidentally, the battery cells  8  are contained in two rows in the battery pack  1 , irrespectively of whether the battery pack  1  is the large size battery pack  1   a  or the small size battery pack  1   b ; therefore, the area of the lower surface  2   a  serving as a mount surface for mounting into the battery mounting portion  5  is set substantially the area occupied by two battery cells  8  disposed side by side. Accordingly, even in the camcorder  7  for which the large size battery pack  1   a  is used, the area of the battery mounting portion  5  need not be so large, and other switches can be arranged at the back surface  7   a  of the main body of the camcorder  7 . 
     Now, the configuration of the battery pack  1  will be specifically described below. The housing  2  of the battery pack  1  is formed from a synthetic resin. As shown in  FIGS. 1B and 3B , one side surface of the battery pack  1  which is adjacent to the front surface  2   b  and the back surface  2   e  and which is directed vertically upwards at the time of mounting the battery pack  1  into the battery mounting portion  5  is provided with an identification portion  10  for identifying gripping surfaces according to the mounting direction. In addition, the front surface  2   b  and the back surface  2   e  of the housing  2  are provided with anti-slip portions  11  at positions to be gripped by the user. With the identification portion  10  and the anti-slip portion  11  thus formed, it can be seen if the housing  2  is gripped correctly in mounting the battery pack  1  into the battery mounting portion  5 . Besides, the housing  2  can be gripped assuredly even where the housing  2  has an increased weight. 
     Specifically, at the time of mounting the battery pack  1  into the battery mounting portion  5 , the battery pack  1  is inserted in such a manner that its lower surface  2   a  serving as the mount surface is used as the insertion end, and the front surface  2   b  provided with the terminal portions  6  is slid in a horizontal direction, as above-mentioned. Therefore, it would be necessary for the user to grip the battery pack  1  in the condition where the front surface  2   b  is directed toward the terminal side in the battery mounting portion  5 . 
     The identification portion  10  is for permitting the user to discriminate the gripping surfaces of the housing  2  at the time of mounting the battery pack  1  into the battery mounting portion  5 . The identification portion  10  is formed by a method in which one side surface  2   c  is provided with a recessed surface portion  10   a , the inside of the recessed surface portion  10   a  is grained, and, further, the recessed surface portion  10   a  is provided with grains composed of protrusions extending in the front-rear direction. When the user grips the battery pack  1  with his right hand, the index finger or the middle finger is put on the one side surface  2   c  so that the identification portion  10  makes contact with the fingertip; as a result, it can be intuitively perceived that the housing  2  is correctly gripped with its one side surface  2   c  directed vertically upwards, and the sliding direction upon insertion of the housing  2  into the battery mounting portion  5  can also be grasped intuitively. 
     In addition, as above-mentioned, where the battery pack  1  is the large size battery pack  1   a , a total of eight battery cells  8  are contained in two rows and four layers, and where the battery pack  1  is the small size battery pack  1   b , a total of four battery cells  8  are contained in two rows and two layers. As a result, the large size battery pack  1   a  is about 550 g in weight, while the small size battery pack  1   b  is 300 g in weight, heavier than a private-use battery in which battery cells are contained in two rows and one layer. Accordingly, the battery packs should be prevented from slipping down from the user&#39;s hand. 
     The anti-slip portions  11  formed in the front surface  2   b  and the back surface  2   e  are for preventing the slipping-down of the battery pack  1  by making the housing  2  easier to grip by the user&#39;s hand at the time of mounting the battery pack  1  into the battery mounting portion  5 . The anti-slip portions  11  are formed by forming recessed surface portions  11   a  at upper portions of the front surface  2   b  and the back surface  2   e , and graining the inside of the recessed surface portions  11   a . When gripping the battery pack  1  with the right hand, the user put the thumb on the anti-slip portion  11  in the front surface  2   b , and put the middle finger or the third finger and the little finger on the anti-slip portion  11  in the back surface  2   e , whereby the rugged surfaces of the anti-slip portions  11  function to give frictional resistance, ensuring that the housing  2  can be held securely without slipping. Incidentally, as the shape of the grains imparted to the recessed surface portions  11   a  of the anti-slip portions  11 , any of a variety of shapes can be adopted. 
     Incidentally, the housing  2  is provided with a grain different from those of the identification portion  10  and the anti-slip portions  11 , in other regions than the identification portion  10  and the anti-slip portions  11  of the upper cover  3 . 
     Now, the configuration of the lower surface  2   a  serving as the mount surface for mounting into the battery mounting portion  5  will be described below. The lower surface  2   a  is provided with a pair of insertion guide grooves  15  and  16  which extend along and are spaced from each other along the direction of sliding between the mounting position and the lading/unloading position inside the battery mounting portion  5 , and other region than the insertion guide grooves  15  and  16  is used as a region for adhering an identification label  14  (see  FIG. 2 ). Into the insertion guide grooves  15  and  16 , guide protrusions  30  and  31  projectingly provided on the bottom surface  5   a  of the battery mounting portion  5  are inserted, whereby the operations of mounting and dismounting the housing  2  are guided, and the housing  2  mounted in the battery mounting portion  5  is prevented from chattering in the direction of both side surfaces  2   c  and  2   d.    
     As shown in  FIGS. 6A and 6B , the housing  2  has the lower surface  2   a  provided with the insertion guide grooves  15  and  16  spaced from each other along the sliding direction, whereby a substantially central portion can be made to be wide, and a side adhering region for the identification label  14  can be secured. In addition, since the lower surface of the housing  2  is not cut up into left and right portions by the insertion guide grooves  15  and  16 , as shown in  FIG. 2 , a large single identification label  14  formed in a substantially H shape can be adhered. 
     Furthermore, since the housing  2  has the lower surface  2   a  provided with the insertion guide grooves  15  and  16  spaced from each other along the sliding direction, as shown in  FIG. 7 , that region of the inside surface of the lower surface  2   a  which is occupied by protrusions present due to the insertion guide grooves  15  and  16  projecting to the inside of the housing  2  can be minimized. Therefore, in the housing  2 , a wide electronic part mounting region and a wide patterning region can be secured on the lower surface  2   a  side of the circuit board  9  disposed on the inside of the lower surface  2   a , and efficient use of space can be realized. 
     The insertion guide grooves  15  and  16  are formed substantially in the center in the width direction of the lower surface  2   a  along the front-rear direction. In addition, the front surface side insertion guide groove  15  formed on the front surface  2   b  side has an end face fronting on a lower portion of the front surface  2   b , while the back surface side insertion guide groove  16  formed on the back surface  2   e  side has an end face fronting on a lower portion of the back surface  2   e  and is provided with a lock recess  17  by which a lock piece  35  provided in the battery mounting portion  5  is locked. 
     The front surface side insertion guide groove  15  is provided with an L-shaped opening  18  where its insertion end fronting on the front surface  2   b  is opened in a substantially L shape, and a front surface side guide groove portion  20  continued through a stepped portion  19  formed on the back surface side relative to the L-shaped opening  18 . As shown in  FIG. 8 , a front surface side guide protrusion  30  formed at the deepest portion in the sliding direction of the battery mounting portion  5  is passed through the front surface side insertion guide groove  15 . The front surface side guide protrusion  30  is provided with a front surface side protruding bar  32  to be inserted in the front surface side guide groove portion  20 , and a lock protrusion  33  substantially L-shaped in section which is formed on the deeper side of the front surface side protruding bar  32  and which is locked by the L-shaped opening  18 . The front surface side insertion guide groove  15  is so formed that when the housing  2  is inserted to the loading/unloading position in the battery mounting portion  5  and is slid toward the front surface  2   b  side to the mounting position, the front surface side protruding bar  32  of the front surface side guide protrusion  30  is inserted in the front surface side guide groove portion  20 , an end face of the lock protrusion  33  abuts on the stepped portion  19 , and the lock protrusion  33  is locked by the L-shaped opening  18 . 
     The back surface side insertion guide groove  16  is provided with the lock recess  17  for locking the lock piece  35 , by forming an end portion fronting on the back surface  2   e  in a substantially rectangular shape, and with a back surface side guide groove portion  21  formed on the front surface side relative to the lock recess  17 . The back surface side guide groove portion  21  is formed in line with the front surface side guide groove portion  20 . In addition, the lock recess  17  is formed to be wider than the back surface side guide groove portion  21 , and is formed to be continuous with the back surface side guide groove portion  21 , whereby a lock wall  22  for locking the lock piece  35  is provided on the front surface side of the housing  2 . 
     Into the back surface side insertion guide groove  16 , a back surface side guide protrusion  31  formed in the battery mounting portion  5  is inserted. The back surface side guide protrusion  31  is provided with a back surface side protruding bar  34  to be passed through the back surface side guide groove portion  21 , and the lock piece  35  to be locked by the lock recess  17 . The back surface side protruding bar  34  is formed in line with the front surface side protruding bar  32 . Besides, the lock piece  35  is inserted in the battery mounting portion  5  through a lock hole  36  opened in the bottom surface  5   a  of the battery mounting portion  5 , as shown in  FIG. 8 , whereby its tip portion is brought into abutment on the lock wall  22 . The lock piece  35  can be turned into and out of the battery mounting portion  5  by a turning mechanism  40 . 
     The turning mechanism  40  is mounted to a back surface wall of the battery mounting portion  5 , and includes a support plate  41  for supporting the lock piece  35 , a push bar  42  for pushing the lock piece  35 , and an operating button  43  for operating the push bar  42 . The support plate  41  supports a turning shaft  44  passed through a turning bearing  35   a  formed at a rear end portion of the lock piece  35 . In addition, the turning shaft  44  is fitted with a coil spring  45  of which one end is locked on the support plate  41  and the other end is locked on the lock piece  35 . This ensures that the lock piece  35  is constantly turningly urged by the coil spring  45  in the direction of an arrow L in  FIG. 8  so that its tip portion is made to front on the inside of the battery mounting portion  5  through the lock hole  36 . The push bar  42  for pushing the lock piece  35  is for turning the lock piece  35 , which is urged toward the direction of the arrow L, in the direction opposite to the arrow L, and is supported by the support plate  41  so as to be movable up and down between the support plate  41  and a side surface of the battery mounting portion  5 . The push bar  42  abutting on the lock piece  35  at its one end is provided with an inclined surface portion  42   a  at its other end opposite to the one end, and the operating button  43  abuts on the inclined surface portion  42   a . The operating button  43  is for turning the lock piece  35  in the direction opposite to the arrow L by sliding the push bar  42  through pushing the inclined surface portion  42   a  of the push bar  42 . The operating button  43  is supported on a side surface of the battery mounting portion  5  by a support member (not shown), and is constantly urged by the coil spring  45  in such a direction that its tip portion is spaced away from the inclined surface portion  42   a  of the push bar  42 . 
     The back surface side insertion guide groove  16  is so configured that, when the housing  2  is inserted into the battery mounting portion  5  and is slid toward the front surface  2   b  side, the back surface side protruding bar  34  is inserted in the back surface side guide groove portion  21 , and the lock piece  35  is inserted in the lock recess  17  so as to abut on the lock wall  22  formed between the lock recess  17  and the front surface side guide groove portion  20 . 
     As a result, the housing  2  is guided in the sliding inside the battery mounting portion  5 , and is prevented from chattering in a direction orthogonal to the sliding direction. More specifically, with the front surface side guide protrusion  30  inserted in the front surface side insertion guide groove  15  and with the back surface side guide protrusion  31  inserted in the back surface side insertion guide groove  16 , the housing  2  is prevented from chattering in the direction of both side surfaces  2   c  and  2   d.    
     In addition, with the lock protrusion  33  engaged with the L-shaped opening  18 , the housing  2  is prevented from chattering in the direction of both side surfaces  2   c  and  2   d  and from chattering in the direction of the upper and lower surfaces  2   f  and  2   a . Therefore, the housing  2  can be secured in reliability of connection to the battery mounting portion  5 . Besides, with the L-shaped opening  18  is made to be exposed side by side with the terminal portions  6   a  to  6   e , stresses pertaining to the terminal portions  6   a  to  6   e  can be suppressed, and reliability of electrical connection can be secured. 
     Furthermore, when the housing  2  is slid to the mounting position, the lock piece  35  abuts on the lock wall  22 , whereby the housing  2  is prevented from sliding in the direction of the back surface  2   e , namely, in the direction from the mounting position toward the loading/unloading position, and is prevented from slipping off the battery mounting portion  5  due to vibration, shock or the like. In addition, the housing  2  is prevented from chattering in the battery mounting portion  5 , also by the locking of the lock piece  35  in the lock recess  17 . 
     Incidentally, in detaching (unloading) the battery pack  1  from the battery mounting portion  5 , the operating button  43  of the turning mechanism  40  is depressed, upon which the tip of the operating button  43  pushes the inclined surface portion  42   a  of the push bar  42 , and the push bar  42  is slid toward the bottom surface  5   a  side. As a result, the lock piece  35  pushed by the push bar  42  so as to be urged turningly in the direction opposite to the arrow L, so that the lock piece  35  is retracted from the inside of the battery mounting portion  5 , and is disengaged from the lock recess  17  of the housing  2 . This results in that the housing  2  can be slid in the direction of the back surface  2   e.    
     Thus, the back surface side insertion guide groove  16  is provided with the lock recess  17  continuous with the back surface side guide groove portion  21 , whereby it is promised that the housing  2  is prevented from chattering in the battery mounting portion  5  and from sliding in the direction of the back surface  2   e . In addition, that region of the lower surface  2   a  which is occupied by the back surface side insertion guide groove  16  can be reduced, and efficient utilization of the lower surface  2   a  can be contrived. Therefore, the housing  2  is provided with a wider region for adhering the identification label  14  onto the lower surface  2   a , and with an enlarged region for disposing the circuit board  9  on the inside of the lower surface  2   a.    
     Now, the configuration of both side surfaces  2   c  and  2   d  of the housing  2  will be described below. The housing  2  is provided with a detection recess or recesses  50  for detecting the kind of the battery pack  1 , at an edge or edges formed between the lower surface  2   a  and one or both of the side surfaces  2   c  and  2   d . As above-mentioned, the battery packs  1  prepared are classified into the large size battery packs  1   a  and the small size battery packs  1   b , according to the magnitude of battery capacity. In the large size battery pack  1   a , the detection recesses  50  are provided respectively in both side surfaces  2   c  and  2   d , as shown in  FIG. 6A ; in the small size battery pack  1   b , on the other hand, the detection recess  50  is provided only on the side of the other side surface  2   d , as shown in  FIG. 6B . 
     In addition, as shown in  FIG. 9 , the battery mounting portion  5  is provided with mis-insertion preventive engaging protrusions  51  corresponding to the detection recess  50 , on side surfaces opposed to the side surfaces  2   c  and  2   d . With such engaging protrusions  51  projectingly provided, mis-mounting of a battery pack of a non-compatible size can be obviated. Specifically, since the large size battery pack  1   a  is provided with a pair of the detection recesses  50  in both side surfaces  2   c  and  2   d , the battery mounting portion  5  of an electronic apparatus corresponding to the large size battery pack  1   a  is provided with a pair of the engaging protrusions  51  for engagement with both detection recesses, whereby the small size battery pack  1   b  provided with the detection recess  50  only in the other side surface  2   d  can be prevented from being erroneously mounted into the battery mounting portion  5  in consideration. In this case, the engaging protrusion  51  projectingly provided on the side surface opposite to the other side surface  2   d  of the small size battery pack  1   b  interferes with the edge formed between the other side surface  2   d  and the lower surface  2   a  of the housing  2 , whereby the small size battery pack  1   b  is prevented from being mounted into the battery mounting portion  5 . As a result, in the case of a camcorder  7  for business use, for example, the power consumption is large and, therefore, only the large size battery pack  1   a  having a great battery capacity can be mounted. 
     Other configurations than the above may also be considered. For example, the L side battery packs  1   a  may be business-use batteries with comparatively large size and capacity, while the small size battery packs  1   b  may be private-use batteries with comparatively small size and capacity. In this case, a system may be adopted in which only the large size battery packs  1   a  can be mounted in the electronic apparatuses for business use, while both size battery packs  1   a  and  1   b  can be mounted in electronic apparatuses for private use. 
     In addition, the housing  2  is provided with the detection recess(es)  50  not in the front surface  2   b  where a type discriminating rugged pattern has generally been provided, but at the edge(s) formed between the lower surface  2   a  and one or both of the side surfaces  2   c  and  2   d . This ensures that the housing  2  can be securely provided in its front surface  2   b  with a space where five terminal portions  6  and an end face of the front surface side insertion guide groove  15  are frontingly provided side by side. 
     Incidentally, the battery mounting portion  5  may have a configuration in which type discriminating switches  52  corresponding to the detection recesses  50  are projectingly provided on side surfaces opposed to both side surfaces  2   c  and  2   d  of the housing  2 , in place of the engaging protrusions  51 . In this case, when the battery pack  1  is mounted in the battery mounting portion  5 , none of the switches  52  is pushed in the case of the large size battery pack  1   a , whereas the switch  52  on the side surface opposed to the one side surface  2   c  of the housing  2  is pushed in the case of the small size battery pack  1   b . By detecting the pushed states of the switches  52 , it can be discriminated on the electronic apparatus size which of the large size battery pack  1   a  and the small size battery pack  1   b  has been mounted. 
     As a result, a treatment in which an alarm is issued to the user on the electronic apparatus side, a treatment in which supply of electric power from the small size battery pack  1   b  is not accepted and no operation is conducted, or the like treatment can be carried out in the case where the small size battery pack  1   b  is mounted. 
     Now, lock recesses  55  and  56  formed on both sides of the detection recess  50  in the housing  2  and operative to lock the housing  2  in the battery mounting portion  5  will be described below. The lock recesses  55  and  56  are formed on both sides of the detection recess  50  at each of the edges formed between the lower surface  2   a  and the side surfaces  2   c  and  2   d . The lock recesses  55  and  56  ensure that when the housing  2  is inserted into the battery mounting portion  5  and is slid to the mounting position, lock protrusions  70  projectingly provided on side surfaces of the battery mounting portion  5  correspondingly to the lock recesses  55  and  56  are locked. 
     As shown in  FIG. 9 , the front surface side lock recess  55  provided on the side of the front surface  2   b  of the housing  2  includes an inclined surface portion  57  for drawing in the lock protrusion  70 , a clamped portion  58  to be clamped between the lock protrusion  70  and the bottom surface  5   a  of the battery mounting portion  5 , and an orthogonal surface portion  59  continuous with the inclined surface portion  57  and extended in the height direction substantially orthogonal to the lower surface  2   a . The front surface side lock recess  55  is provided with an opening  60  through which the lock protrusion  70  is put into and out of a clamped state between the inclined surface portion  57  and the clamped portion  58 . 
     Further, the back surface side lock recess  56  provided on the side of the back surface  2   e  of the housing  2  includes an inclined surface portion  61  for drawing in the lock protrusion  70 , a clamped portion  62  to be clamped between the lock protrusion  70  and the bottom surface  5   a  of the battery mounting portion  5 . The back surface side lock recess  56  is provided with an opening  63  through which the lock protrusion  70  is put into and out of a clamped state between the inclined surface portion  61  and the clamped portion  62 . 
     Each of the lock protrusions  70  to be locked at the front surface side lock recess  55  and the back surface side lock recess  56  includes a base portion  71  provided erectingly from the bottom surface  5   a  of the battery mounting portion  5 , and a lock portion  72  extended from the base portion  71  toward the back surface side of the battery mounting portion  5  and located at upper surfaces of the clamped portions  58  and  62 . The lock portion  72  is so configured that its distance from the bottom surface  5   a  of the battery mounting portion  5  is roughly equal to or slightly smaller than the thickness of the clamped portions  58  and  62  of the housing  2  of which the lower surface  2   a  is mounted on the bottom surface  5   a  of the battery mounting portion  5 . When the housing  2  is slid to the battery mounting position, the clamped portions  58  and  62  are each pressed into the gap between the lock portion  72  and the bottom surface  5   a  of the battery mounting portion  5 , so as to hold the clamped portions  58  and  62 , thereby locking the housing  2  in the battery mounting portion  5 . 
     When the housing  2  is inserted in the direction of an arrow D in  FIG. 9  until it comes to the loading/unloading position where its lower surface  2   a  as the mount surface abuts on the bottom surface  5   a  of the battery mounting portion  5 , the lock portions  72  of the lock protrusions  70  go forward through the openings  60  and  63 . In this case, the inclined surface portions  57  and  61  and the orthogonal surface portion  59  of the housing  2  slide on the lock protrusions  70 , whereby the lock portions  72  are made to be at the same height as the upper surfaces of the clamped portions  58  and  62  and are guided to such positions as to permit mutual locking. Incidentally, the detection recess  50  is also made to go forward toward the engaging protrusion  51  projectingly provided on the side wall of the battery mounting portion  5 . Next, the housing  2  is slid in the direction of an arrow S in  FIG. 9 , namely, toward the side of the front surface  2   b . As a result, terminal pins  101  on the side of the battery mounting portion  5  are inserted into and engaged with the terminal portions  6  made to front on the front surface  2   b , and the clamped portions  58  and  62  of the lock recesses  55  and  56  come to be clamped between the lock portions  72  of the lock protrusions  70  and the bottom surface  5   a  of the battery mounting portion  5 . 
     Incidentally, it suffices for the lock portions  72  to be capable of clamping the clamped portions  58  and  62  between themselves and the bottom surface  5   a  of the battery mounting portion  5 , and they may not necessarily be clamped between the upper surfaces of the clamped portions  58  and  62  and the ceiling surfaces of the lock recesses  55  and  56  opposed to the upper surfaces. Therefore, a configuration may be adopted in which the lock portions  72  do not have a thickness and that gaps are left between the lock portions  72  and the ceiling surfaces of the lock recesses  55  and  56 . It is to be noted here that, naturally, the lock portions  72  may be clamped between the upper surfaces of the clamped portions  58  and  62  and the ceiling surfaces of the lock recesses  55  and  56 . 
     At the time of detaching (unloading) the housing  2  from the battery mounting portion  5 , the housing  2  is slid in the direction opposite to the arrow S in  FIG. 9  from the mounting position to the loading/unloading position, whereby the clamped portions  58  and  62  are drawn out of the gaps between the lock portions  72  and the bottom surface  5   a  of the battery mounting portion  5 . In this instance, the lock portions  72  of the lock protrusions  70  are located in the openings  60  and  63  of the lock recesses  55  and  56 , so that the housing  2  can be moved in the direction opposite to the arrow D, namely, in the direction toward the side of the upper surface  2   f.    
     Here, the front surface side lock recess  55  is provided with the orthogonal surface portion  59  continuous with the inclined surface portion  57  and orthogonal to the lower surface  2   a . Near the orthogonal surface portion  59 , the circuit board  9  is disposed on the inside of the housing  2 . In the housing  2 , the circuit board  9  is disposed at a height where the inclined surface portion  57  and the orthogonal surface portion  59  meet each other. Specifically, since the housing  2  is provided with the orthogonal surface portion  59  extending in the height direction orthogonal to the lower surface  2   a , the circuit board  9  can be held on the inside of the orthogonal surface portion  59  at the height of the meeting point between the inclined surface portion  57  and the orthogonal surface portion  59 , whereby the circuit board  9  can be disposed at the height at which the front surface side lock recess  55  is formed. 
     In the large size battery pack  1   a  enlarged in size and weight correspondingly to the business-use camcorder  7 , in order to secure reliability of connection between the lock recesses  55  and  56  of the housing  2  and the lock protrusions  70  on the side of the battery mounting portion  5 , it would be necessary to make the clamped portions  58  and  62  thicker as compared with the related art and to form the lock portions  72  of the lock protrusions  70  to be larger as compared with the related art. Attendant on the increase in the thickness of the clamped portions  58  and  62  and enlargement of the lock portions  72 , the lock recesses  55  and  56  are also enlarged in size in the height direction of the housing  2 . Since the lock recesses  55  and  56  are projected to the inside of the housing  2  in the same shape, an attempt to ensure that the circuit board  9  disposed on the lower surface  2   a  side is arranged while avoiding the projected shape results in that the lock recesses  55  and  56  are naturally disposed on the upper side. 
     However, when it is attempted to set the circuit board  9  more on the upper side of the lower surface  2   a , the region for arranging the battery cells  8  connected to the circuit board  9  are also disposed more on the upper side, which leads to an increase in the size of the housing  2  and, on the other hand, generates a dead space between the circuit board  9  and the lower surface  2   a . In connection with this, when the housing  2  has a configuration in which an increase in the size of the lock recesses  55  and  56  is contrived and the orthogonal surface portion  59  is provided to thereby arrange the circuit board  9  on the inside of the orthogonal surface portion  59 , the height at which to dispose the circuit board  9  can be set closer to the lower surface  2   a , and the housing  2  can be prevented from becoming larger in size. In addition, with the orthogonal surface portion  59  formed in continuity with the inclined surface portion  57 , the circuit board  9  can be held at the height of the meeting point between the inclined surface portion  57  and the orthogonal surface portion  59 , and an increase in the size of the lock recesses  55  and  56  can be attained while maintaining the area and the arranging position of the circuit board  9 . Incidentally, the orthogonal surface portion may be formed not only in the front surface side lock recess  55  but also in the back surface side lock recess  56 . 
     Besides, the lock recesses  55  and  56  have the clamped portions  58  and  62  formed to have a thickness larger than the depth of the detection recess  50  in the height direction orthogonal to the lower surface  2   a . This can prevent the lock protrusion  70  from being erroneously inserted into the detection recess  50  in putting the housing  2  in position. 
     More specifically, in the case where the lower surface  2   a  is mounted on the bottom surface  5   a  without the housing  2  being guided by a side wall of the battery mounting portion  5  or the like case, the lock protrusion  70  might be erroneously inserted into the detection recess  50 . In this case, as shown in  FIG. 10A , a configuration in which the depth of the detection recess  50  is smaller than the thickness of the clamped portions  58  and  62  ensures that the housing  2  cannot be inserted to the loading/unloading position where its lower surface  2   a  abuts on the bottom surface  5   a  of the battery mounting portion  5  and that an inclination of the housing  2  or the like abnormality is found, which permits the user to recognize that appropriate insertion has not been made. 
     On the other hand, if the depth of the detection recess  50  is larger than the thickness of the clamped portions  58  and  62 , as shown in  FIG. 10B , the housing  2  can be inserted to the loading/unloading position where its lower surface  2   a  abuts on the bottom surface  5   a  of the battery mounting portion  5  even in the case where the lock protrusion  70  is erroneously inserted into the detection recess  50 . As above-mentioned, the lock portions  72  of the lock protrusions  70  are necessary only to be capable of clamping the clamped portions  58  and  62  and may not necessarily be thick, and, therefore, they can be formed in a suppressed thickness. Accordingly, where the depth of the detection recess  50  is formed to be larger, if only a little, than the thickness of the clamped portions  58  and  62 , the housing  2  can be inserted to the bottom surface  5   a  of the battery mounting portion  5  while the lock protrusion  70  is kept erroneously inserted in the detection recess  50 . 
     However, in the present battery pack  1 , the thickness of the clamped portions  58  and  62  is set to be larger than the depth of the detection recess  50 , so that if the lock protrusion  70  is erroneously inserted in the detection recess  50 , the housing  2  cannot be inserted to the bottom surface  5   a  of the battery mounting portion  5 . Accordingly, the user can easily discriminate whether or not the housing  2  is erroneously inserted in the battery mounting portion  5 . 
     Now, the depth of the detection recess  50  and the depths of the front surface side lock recess  55  and the back surface side lock recess  56  in the width direction of the lower surface  2   a  will be described below. As shown in  FIG. 6 , the housing  2  has a configuration in which the depth of the detection recess  50  in the width direction of the lower surface  2   a , i.e., the depth of the detection recess(es)  50  in the lower surface  2   a  from the side surface(s)  2   c  and  2   d  in the direction orthogonal to the direction of sliding of the housing  2  between the loading/unloading position and the mounting position, is set to be larger than the depth of the front surface side lock recess  55  and the back surface side lock recess  56  in the same direction. As has been above-mentioned, the detection recess  50  is for engagement with the engaging protrusion  51  projectingly provided on the side wall of the battery mounting portion  5 . In the large size battery pack  1   a , both side surfaces  2   c  and  2   d  of the housing  2  are each provided with the detection recess  50 , whereas in the small size battery pack  1   b , only the other side surface  2   d  of the housing  2  is provided with the detection recess  50 . Besides, the engaging protrusion  51  for engagement with the detection recess  50  is projectingly provided at each of those side surfaces of the battery mounting portion  5  of the electronic apparatus used with the large size battery pack  1   a  which face the side surfaces  2   c  and  2   d  of the housing  2 ; on the other hand, the detection recess  50  is projectingly provided only at that side surface of the battery mounting portion  5  of the electronic apparatus used with the small size battery pack  1   b  which faces the other side surface  2   d  of the housing  2 . 
     Each of these engaging protrusions  51  is so formed that its protrusion amount from the side surface of the battery mounting portion  5  is roughly equal to the depth of the detection recess  50  in the width direction of the lower surface  2   a . Therefore, when the engaging protrusion  51  is inserted in the detection recess  50 , it is substantially entirely engaged in the detection recess  50 . In addition, if a non-compatible small size battery pack  1   b  is about to be inserted in the battery mounting portion  5 , the engaging protrusion  51  abuts on that one side surface  2   c  of the housing  2  which is not provided with the detection recess  50 , whereby insertion of the non-compatible small size battery pack  1   b  into the battery mounting portion  5  is prevented. 
     Here, the protrusion amount of the engaging protrusion  51  is set to be approximately equal to the depth of the detection recess  50  in the width direction of the lower surface  2   a , and the depth of the detection recess  50  is set to be larger than the depth of the lock recesses  55  and  56  in the same direction. In other words, the engaging protrusion  51  is formed to protrude by an amount larger than the depth of the lock recesses  55  and  56 . Besides, the lock protrusions  70  are formed to have a protrusion amount according to the depth of the lock recesses  55  and  56  in the width direction of the lower surface  2   a . Accordingly, the engaging protrusion  51  is formed to have a protrusion amount larger than that of the lock protrusion  70 . 
     Therefore, as shown in  FIG. 11A , when the small size battery pack  1   b  is mounted in the battery mounting portion  5  of an electronic apparatus for exclusive use with the large size battery pack  1   a , the engaging protrusion  51  protruding from a side surface of the battery mounting portion  5  abuts on one side surface  2   c  of the housing  2 . In this case, since the engaging protrusion  51  is formed to have a protrusion amount larger than that of the lock protrusions  70 , the lock protrusions  70  are also not inserted into the lock recesses  55  and  56 . Since none of the engaging protrusion  51  and the lock protrusions  70  is engaged with the detection recess  50  and the lock recesses  55  and  56 , the housing  2  cannot be mounted into the battery mounting portion  5 . Therefore, in the camcorder  7  or the like as shown in  FIG. 5 , for example, wherein the lower surface  2   a  is inserted in a horizontal direction, the housing  2  is not held by the battery mounting portion  5  even if it is being inserted, and it is difficult to slide the housing  2  toward the side of the front surface  2   b . Therefore, the user can easily judge that the small size battery pack  1   b  is being erroneously inserted into the electronic apparatus for exclusive use with the large size battery pack  1   a.    
     On the other hand, in the case where the depth of the detection recess  50  in the width direction of the lower surface  2   a  is set to be smaller than the depth of the lock recesses  55  and  56  in the same direction, the engaging protrusion  51  on the battery mounting portion  5  side is also formed to have a protrusion amount smaller than that of the lock protrusions  70 . Therefore, as shown in  FIG. 11B , where the small size battery pack  1   b  is mounted in the battery mounting portion  5  of an electronic apparatus for exclusive use with the large size battery pack  1   a , the lock protrusions  70  would be inserted into the lock recesses  55  and  56  even if the engaging protrusion  51  abuts on the one side surface  2   c . Accordingly, it is difficult for the user to judge that erroneous insertion of the battery pack  1  is occurring, and might irrationally slide the housing  2  toward the front surface  2   b  side so as to mount the housing  2  into the battery mounting portion  5 . 
     In connection with this point, in the battery pack  1  based on the embodiment according to the present invention, the detection recess  50  is formed to be deeper than the lock recesses  55  and  56 , so that the engaging protrusion  51  is also protruding more than the lock protrusions  70 , and, when the engaging protrusion  51  abuts on the one side surface  2   c , the lock protrusions  70  are also prevented from being inserted into the lock recesses  55  and  56 . This ensures that, in the case of the battery pack  1 , erroneous mounting of the small size battery pack  1   b  into the electronic apparatus for exclusive use with the large size battery pack  1   a  can be prevented. 
     Now, the terminal portions  6  formed at a lower portion of the front surface  2   b  of the housing  2  will be described below. As shown in  FIG. 12 , the terminal portion  6  includes a terminal hole  80  which is formed in the lower case  4  of the housing  2  and is made to front on the outer side of the front surface  2   b , and a metallic bearing  82  which is fitted in a terminal case  81  disposed on the inside of the terminal hole  80  and in which the terminal pin  101  formed on the battery mounting portion  5  side is inserted. 
     As shown in  FIG. 13 , the terminal hole  80  includes a recessed surface portion  84  provided with an insertion hole  83  in which the terminal pin  101  is inserted, and a guide portion  85  which is formed at the inner peripheral surface of the insertion hole  83  and which is continuous with the recessed surface portion  84  and the metallic bearing  82 . The recessed surface portion  84  is a roughly rectangularly shaped recess formed in the front surface  2   b  of the housing  2 , and a roughly central portion of the bottom surface thereof is opened in a circular shape to form the insertion hole  83  in which the terminal pin  101  is to be inserted. The guide portion  85  includes an inclined surface portion  86  which is formed at the inner peripheral surface of the insertion hole  83  and which guides the terminal pin  101  into the metallic bearing  82 , and a support surface portion  87  which is formed to be substantially equal to the metallic bearing  82  in diameter and which supports the terminal pin  101  together with the metallic bearing  82 . 
     The insertion hole  83  opened in the recessed surface portion  84  has an upper end opened to be larger in diameter than the terminal pin  101 , so that the terminal pin  101  is easily inserted therein. Besides, the insertion hole  83  permits the terminal pin  101  to be inserted into the terminal portion  6  without any load thereon, through a process wherein the terminal pin  101  is guided through the inclined surface portion  86  formed on the upper end side of the insertion hole  83  into the support surface portion  87  which is formed to be roughly equal to the metallic bearing  82  in diameter and which is continuous with the metallic bearing  82 . 
     The metallic bearing  82  disposed in continuity with the support surface portion  87  is a hollow cylindrical metallic member of which one end in the longitudinal direction is opened and the other end is closed. The metallic bearing  82  is fitted in the terminal case  81 , and is connected on its closed end side through a metallic tab  88  to the circuit board  9  connected with the terminal case  81  (see  FIG. 17B ). As shown in  FIG. 14 , the metallic bearing  82  is so configured that the terminal case  81  is disposed inside the lower case  4  together with the circuit board  9 , whereby it is made to be continuous with the support surface portion  87  of the terminal hole  80  as shown in  FIG. 12 , for insertion and holding of the terminal pin  101  inserted in the insertion hole  83 . 
     The terminal case  81  in which to fit the metallic bearing  82  is a roughly rectangularly shaped resin part formed to have a length in the longitudinal direction roughly equal to the length in the width direction of the lower case  4 . As shown in  FIGS. 15 and 12 , the terminal case  81  is provided with fitting holes  89  for containing the metallic bearings  82  along the longitudinal direction thereof. The fitting hole  89  has a hollow cylindrical shape with an inside diameter roughly equal to the outer shape of the metallic bearing  82 , and is opened at both ends in the longitudinal direction thereof. Each metallic bearing  82  is continued to the terminal hole  80  via an end face of the fitting hole  89 , and is connected to the metallic tab  88 . 
     In the terminal portion  6 , the insertion hole  83  is opened inside the recessed surface portion  84  of the terminal hole  80 , and is continued to the metallic bearing  82  through the guide portion  85 , whereby the metallic bearing  82  is located on the inner side of the housing  2  relative to the front surface  2   b . This ensures that, in the terminal portion  6 , it is possible to prevent short-circuiting between the metallic bearing  82  and an external metal, deformation of the metallic bearing  82  due to collision against an external portion, or the like trouble. 
     In addition, in the terminal portion  6 , the terminal pin  101  is inserted and held in the support surface portion  87  of the guide portion  85  of the terminal hole  80  and the metallic bearing  82  fitted in the terminal case  81 . With the terminal pin  101  thus inserted and held in two component parts, namely, the terminal hole  80  on the lower case  4  side and the terminal case  81  disposed inside the lower case  4 , even when a vibration is applied to the electronic apparatus at the time of mounting the battery pack  1 , the load exerted on the terminal pin  101  can be lessened, and reliability of electrical connection can be maintained. 
     As shown in  FIG. 16 , the terminal portions  6  include first to fifth terminal portions  6   a  to  6   e  arrayed at a lower portion of the front surface  2   b . The first and second terminal portions  6   a  and  6   b  and the fourth and fifth terminal portions  6   d  and  6   e  are formed symmetrically on left and right sides at the front surface  2   b  of the housing  2 , and the third terminal portion  6   c  is formed at a position deviated from the center of the front surface  2   b  toward the side of the fourth and fifth terminal portions  6   d  and  6   e . In addition, an end face of the above-mentioned front surface side insertion guide groove  15  is made to front on the center of the front surface  2   b.    
     In addition, as above-mentioned, the terminals formed at the terminal portions  6   a  to  6   e  have respectively predetermined functions. Specifically, the first terminal portion  6   a  is a positive electrode terminal of the battery pack  1 , the second terminal portion  6   b  is a clock line terminal in the SMBus line, the third terminal portion  6   c  is a data line terminal in the SMBus line, the fourth terminal portion  6   d  is an ID terminal with an ID resistance connected thereto, and the fifth terminal portion  6   e  is a negative electrode terminal of the battery pack  1 . 
     In using the battery pack  1 , the housing  2  is inserted into the battery mounting portion  5  and is slid toward the front surface  2   b  side, whereby the terminal pins  101  disposed on the battery mounting portion  5  side are inserted into and held in the terminal portions  6   a  to  6   e . As a result, between the battery pack  1  and the electronic apparatus side, electric power can be supplied through the first and fifth terminal portions  6   a  and  6   e ; clock data can be communicated through the second terminal portion  6   b ; a variety of data such as residual battery capacity, fully charged capacity, present charged capacity, the possible serviceable time from now on under the present use condition, number of charge-discharge cycles, etc. and ID data indicating that the battery pack  1  is a genuine product, and so on can be communicated through the third terminal portion  6   c ; and the ID resistance can be detected through the fourth terminal portion  6   d.    
     The ID resistance detected through the fourth terminal portion  6   d  is used for detecting, on the electronic apparatus side, which of a plurality of types of battery packs prepared according to the difference(s) in capacity has been mounted; specifically, different resistances are set correspondingly to the large size battery packs  1   a  and the small size battery packs  1   b . When the terminal pin  101  is inserted into the fourth terminal portion  6   d , the resistance on the battery pack  1  side is measured, on the electronic apparatus side, and it is judged which of the different types of battery packs  1  has been mounted. 
     Here, the fourth terminal portion  6   d  is formed proximate to the fifth terminal portion  6   e  which constitutes the negative electrode terminal. It is based on the fact that, if the ID detecting resistor and the negative electrode line are remote from each other, electromagnetic radiation from signal lines or the like therebetween is propagated as noise, possibly hampering accurate measurement of resistance. Therefore, in the battery pack  1 , with the fourth terminal portion  6   d  arranged proximate to the negative electrode terminal  6   e , the distance between the ID resistor and the negative electrode line can be designed to be short, accurate measurement of resistance can be achieved. 
     In addition, the third terminal portion  6   c  is formed at a position deviated from the center in the width direction of the front surface  2   b  of the housing  2  toward either of the left and right sides, in this embodiment, toward the side of the fourth and fifth terminal portions  6   d  and  6   e , in view of the presence of the front surface side insertion guide groove  15  in a substantially central position in the width direction of the front surface  2   b.    
     As a result, in the battery pack  1 , the terminal portions  6   a  to  6   e  are arranged at irregular intervals, and the terminal pins  101  formed on the battery mounting portion  5  side correspondingly to the terminal portions  6   a  to  6   e  are also arranged at irregular intervals, accordingly. Therefore, when the battery pack  1  is inappropriately in a left-right reversed state, the terminal pins  101  cannot be inserted into the terminal portions, so that the battery pack  1  can be prevented from being erroneously inserted into the battery mounting portion  5  in the left-right reversed state. 
     Besides, between the second terminal portion  6   b  and the third terminal portion  6   c  and between the third terminal portion  6   c  and the fourth terminal portion  6   d , a pair of electrode tabs  91  connected to the electrodes of the battery cells  8  are extended so as not to overlap with any of the third and fourth terminal portions  6   c  and  6   d . As shown in  FIG. 14 , the electrode tabs  91  connected to the electrodes of the battery cells  8  are formed to be narrower on the side of tip portions  91   a  thereof. When the battery cells  8  are contained into the housing  2 , the tip portions  91   a  are bent into the direction of arrows F in the figure, before connection thereof to the circuit board  9 . With the battery cells  8  contained in the housing  2  together with the circuit board  9 , as shown in  FIG. 17A , the tip portions  91   a  of the electrode tabs  91  are extended in positions which are located between the second terminal portion  6   b  and the third terminal portion  6   c  and between the third terminal portion  6   c  and the fourth terminal portion  6   d  and which are not on the same plane as the terminal portions  6   a  to  6   e.    
     Incidentally,  FIG. 17A  is a front view showing the battery cells  8  disposed on the circuit board  9  connected to a terminal case  81 , and  FIG. 17B  is a bottom view of the same condition as viewed from the back side of the circuit board  9 . As shown in  FIG. 17B , the electrode tab  91  is bent from an end portion of the battery cell  8  into the direction of the arrow F along the circuit board  9 , whereby the narrower tip portion  91   a  thereof is laid around so as not to overlap with any of the second to fourth terminal portions  6   b  to  6   d . Therefore, in the battery pack  1 , it is possible to prevent electromagnetic radiations due to the electrode tabs  91  from being propagated as noise to the communication lines, and accurate data communication can be carried out. 
     Now, the battery mounting portion  5  having the terminal pins  101  to be inserted in the terminal portions  6   a  to  6   e  will be described below. As shown in  FIGS. 18 and 19 , the battery mounting portion  5  includes a terminal board  100  having the terminal pins  101  to be inserted in the terminal portions  6  fronting on the front surface  2   b  of the housing  2 , a containing case  102  which contains the housing  2  therein and in which the terminal board  100  is fitted, and a support plate  103  for supporting the terminal board  100  fitted in the containing case  102 . 
     As shown in  FIGS. 20A and 20B , the terminal board  100  has a roughly rectangular overall shape, and on the side of its one surface  104  fronting on the inside of the containing case  102 , the terminal pins  101  are projectingly provided correspondingly to the number and intervals of the terminal portions  6  provided on the battery pack  1  side. Of each of the terminal pins  101 , the base end side is supported by a support recess (not shown) provided in the terminal board  100 , and the tip is directed toward the side of a front surface  100   a  of the terminal board  100  which faces the front surface  2   b  of the housing  2 . In addition, each of the terminal pins  101  is connected to a terminal cord passed through the support recess. Incidentally, as shown in  FIG. 20B , each terminal cord is led out to the exterior of the containing case  102  through a lead-out recess  105  formed on the side of a back surface  100   b  of the terminal board  100 . 
     In addition, substantially in the center in the width direction of the one surface  104  of the terminal board  100 , the above-mentioned front surface side guide protrusion  30  is formed adjacently to the terminal pins  101 . The front surface side guide protrusion  30  is inserted in the front surface side insertion guide groove  15  formed in the lower surface  2   a  of the housing  2 , so as thereby to guide the loading and unloading of the housing  2  into and from the battery mounting portion  5  and to prevent the housing  2  from chattering in the direction of both side surfaces  2   c  and  2   d  and the direction of the upper and lower surfaces  2   f  and  2   a  when the housing  2  is mounted in the battery mounting portion  5 . The front surface side guide protrusion  30  is provided with the front surface side protruding bar  32  and the lock protrusion  33 . 
     Incidentally, a shielding plate  106  for protecting the terminal pins  101  is turnably mounted onto the one surface  104  of the terminal board  100 . The shielding plate  106  is provided for preventing the terminal pins  101  from contact with a conductor, breakage or the like by being exposed to the exterior in the case where the battery pack  1  is not mounted, and is an elongate plate member disposed on the one surface  104  along the array direction of the terminal pins  101 . The shielding plate  106  is supported to be turnable, with the back surface  100   b  side as a fulcrum. In addition, the shielding plate  106  is locked to a coil spring (not shown), whereby it is normally biased for turning in such a direction as to shield the terminal pins  101 . This ensures that when the battery pack  1  is not yet mounted, the shielding plate  106  shields the terminal pins  101  from the exterior, and when the battery pack  1  is mounted, the shielding plate  106  is pushed by the front surface  2   b  of the housing  2  and turned toward the side of the back surface  100   b , thereby exposing the terminal pins  101 . 
     In addition, the terminal board  100  is provided in its bottom surface  100   c  with support recesses  108  brought into contact with support protrusions  112  of the support plate  103 . The terminal board  100  is supported on the support protrusions  112  of the support plate  103 , with some clearance therebetween, whereby it is supported to be swingable in the direction of the bottom surface  100   c . Besides, the terminal board  100  is provided on its bottom surface  100   c  with a lock piece  109  to be locked on the bottom surface  102   c  of the containing case  102 . 
     As shown in  FIG. 21 , the containing case  102  in which to contain the terminal board  100  as above is formed to be slightly larger than the housing  2  of the battery pack  1 , and has a roughly rectangular box-like shape opened on the upper side where the housing  2  is loaded and unloaded. In addition, the containing case  102  is projectingly provided with the above-mentioned lock protrusions  70  and the above-mentioned engaging protrusion  51  on its side walls  102   a  and  102   b  which respectively face the side surfaces  2   c  and  2   d  of the housing  2 . Further, as shown in  FIG. 8 , the turning mechanism  40  for turning the lock piece  35  engaged with the lower surface  2   a  of the housing  2  is disposed at the back wall, facing the back surface  2   e  of the housing  2 , of the containing case  102 . 
     The containing case  102  is provided in its bottom surface  102   c  (which constitutes the bottom surface  5   a  of the battery mounting portion  5 ) and both side walls  102   a  and  102   b  with a fitting hole  110  in which to fit the terminal board  100 . The fitting hole  110  has its bottom surface  102   c  opened in a roughly rectangular shape, and has its side walls  102   a  and  102   b  each opened also in a rectangular shape so as to be continuous with the opening in the bottom surface  102   c . The terminal board  100  is inserted into the containing case  102  through the bottom surface  102   c , and its bottom surface  100   c  is supported on both sides thereof by the side walls  102   a  and  102   b  of the containing case  102 , whereby the terminal board  100  is fitted in the fitting hole  110 . In this case, the lock piece  109  of the terminal board  100  is locked on the bottom surface  102   c  of the containing case  102 . 
     As a result, of the terminal board  100 , the one surface  104  provided with the terminal pins  101  is made to front on the inside of the containing case  102 . In addition, when the terminal board  100  is fitted in the fitting hole  110 , it is supported on the bottom surface  100   c  side thereof by the support plate  103 . 
     As shown in  FIG. 22 , the support plate  103  is a resin part formed in a roughly rectangular plate-like shape, and is attached to the bottom surface  102   c  of the containing case  102  in a cantilever manner, thereby supporting the terminal board  100  in the fitting hole  110 . The support plate  103  is provided, on its surface facing the terminal board  100 , with support protrusions  112  to be brought into contact with the support recesses  108  of the terminal board  100 . In addition, the support plate  103  is provided with an opening  113 , correspondingly to the lock piece  109  of the terminal board  100 , and is provided with a plurality of attaching holes  114  for attachment to the bottom surface  102   c  of the containing case  102 . 
     When the terminal board  100  is fitted in the fitting hole  110 , the support plate  103  is attached to the containing case  102  from the upper side of the terminal board  100 , thereby to support the terminal board  100 . 
     In this case, the support recesses  108  are formed to be wider than the support protrusions  112 , and none of the side walls of the support recesses  108  makes contact with the support protrusions  112 . In addition, the fitting hole  110  is opened on the sides of the side surfaces  102   a  and  102   b  of the containing case  102 . Therefore, the terminal board  100  can be swung in the direction of an arrow X in  FIG. 19 . The swinging range of the terminal board  100  in the direction of the arrow X is restricted by the contact of one of the side walls of the support recesses  108  with the support protrusion  112  or by the contact of the lock piece  109  with the opening  113 . 
     Besides, support plate  103  is so formed as to leave some clearance between the tip surface of the support protrusion  112  and the bottom surface of the support recess  108 . In addition, the support plate  103  is supported on the containing case  102  in a cantilever manner, and has some flexibility. Therefore, the terminal board  100  can be swung also in the direction of an arrow Z in  FIG. 19 . The swinging range of the terminal board  100  in the direction of the arrow Z is restricted by the contact of the bottom surfaces of the support recesses  108  with the tip surfaces of the support protrusions  112  or by the support thereof in the fitting hole  110  formed in the side walls  102   a  and  102   b  of the containing case  102 . 
     Further, the containing case  102  is formed as a resin part. In addition, the containing case  102  is provided with the fitting hole  110  also in its front wall  102   d , facing the back surface  100   b  of the terminal board  100 , and its side walls  102   a  and  102   b , whereby the front end of the containing case  102  is made to be a free end and to have some flexibility. Therefore, the terminal board  100  can be swung also in the direction of an arrow Y in  FIG. 19 . The swinging range of the terminal board  100  is restricted by the flexing range of the front wall  102   d  of the containing case  102 . 
     Thus, the battery pack  1  is so formed that the terminal board  100  can be swung in three directions, namely, in the directions of the arrows X, Y and Z in  FIG. 19 . This ensures that even when the battery pack  1  mounted in the battery mounting portion  5  is swung due to swinging of the electronic apparatus main body, the terminal board  100  is swung following up to the battery pack  1 , keeping the terminal portions  6  and the terminal pins  101  in connection with each other. Therefore, generation of gap at contact points between the terminal portions  6  and the terminal pins  101  is obviated, whereby failure in connection can be prevented. In addition, sliding is prevented from occurring between the terminal portions  6  and the terminal pins  101 , so that these parts can be prevented from being broken or deteriorated. 
     In addition, the terminal board  100  can be swung in the direction of the arrow X in  FIG. 19 , since both the side walls  102   a  and  102   b  of the containing case  102  are opened. Therefore, where the battery pack  1  is mounted in the battery mounting portion  5  of the camcorder  7 , the terminal board  100  can be swung in the vertical direction in which the camcorder  7  is frequently swung. Accordingly, even if the battery pack  1  is swung in the vertical direction in use of the camcorder  7 , the reliability of connection between the terminal portions  6  of the battery pack  1  and the terminal pins  101  of the battery mounting portion  5  would not be spoiled. 
     Incidentally, the battery mounting portion  5  is not limited to the configuration in which the containing case  102  is used for fitting the terminal board  100  and the support plate  103  therein. For example, a configuration may be adopted in which a battery containing portion is formed in the main body of the electronic apparatus, and the terminal board  100  and the support plate  103  are fitted in the battery containing portion. 
     Now, a residual capacity displaying function of the battery pack  1  will be described. Since the battery pack  1  is planned to be used in a business-use camcorder  7 , the battery pack  1  is designed to have an increased battery capacity and to be capable of being used for a prolonged time. Here, when the business-use camcorder  7  is used, a plurality of spare battery packs  1  are prepared, and when one battery has run down, it is replaced with another, and shooting is continued. In this case, the residual capacities (residual charges) of the spare battery packs  1  are confirmed, whereby it is possible to select a spare battery pack with more residual capacity and to discriminate unused battery packs from the exhausted battery pack(s)  1 . 
     The battery pack  1  has such a residual capacity display unit  120  formed on the upper surface  2   f  of the housing  2 . As shown in  FIGS. 1 and 23 , the residual capacity display unit  120  includes display windows  121  to be turned ON for indicating the residual capacity of the battery pack  1 , a residual capacity display switch  122  for turning ON the display window(s)  121 , detecting means  123  for detecting the depressed state of the residual capacity display switch  122 , and control means  124  for controlling the ON/OFF conditions of the display windows  121  according to the results of detection by the detecting means  123 . The residual capacity display unit  120  changes over the ON/OFF conditions of the display windows  121  according to the time for which the residual capacity display switch  122  is depressed, whereby the convenience in use by the user is enhanced. 
     The display windows  121  have LEDs incorporated therein, and the LEDs are individually turned ON or OFF according to the residual battery capacity. As shown in  FIG. 24 , for example, four display windows  121  are provided side by side at the upper surface  2   f  of the housing  2 , and the ON/OFF conditions of the LEDs at the display windows  121  are controlled as follows. When the residual battery capacity (absolute residual capacity ratio) is less than 20%, all the four LEDs are turned OFF; when the residual capacity is 20 to 39%, only the left end LED is turned ON; when the residual capacity is 40 to 59%, the two left-side LEDs are turned ON; when the residual capacity is 60 to 79%, the three left-side LEDs are turned ON; and when the residual capacity is 80 to 100%, all the four LEDs are turned ON. 
     The residual capacity display switch  122  is formed at the upper surface  2   f  of the housing  2 , adjacently to the display windows  121 . The time for which the residual capacity display switch  122  has been depressed by the user is detected by the detecting means  123 . The control means  124  controls the ON time of the LEDs in the display windows  121 , according to the time for which the residual capacity display switch  122  has been depressed. For example, when the time for which the residual capacity display switch  122  has been depressed is 0.5 second or less, the display window(s)  121  are turned ON for 1 second; and when the time for which the residual capacity display switch  122  has been depressed is more than 0.5 second, the display window(s)  121  are turned ON for 5 second. 
     The detecting means  123  for detecting the time for which the residual capacity display switch  122  has been depressed and the control means  124  for controlling the ON time of the display windows  121  are provided on a circuit board (see  FIG. 2 ) disposed on the upper surface  2   f  side in the inside of the housing  2 , or on the circuit board  9  connected to this circuit board through a flexible wiring board. 
     In the residual capacity display unit  120 , as shown in  FIG. 25 , the control means  124  monitors the ON/OFF states of the LEDs (step S 1 ). Where all the LEDs are OFF, the control means  124  determines whether or not the residual capacity display switch  122  has been depressed (step S 2 ). Where the residual capacity display switch  122  has not been depressed, the control means  124  again monitors the ON/OFF states of the LEDs, and where the residual capacity display switch  122  has been depressed, the control means  124  determines whether or not the residual capacity ratio of the battery pack  1  is less than 20% (step S 3 ). Where the residual capacity ratio of the battery pack  1  is less than 20%, the control means  124  keeps all the LEDs in the OFF state, and where the residual capacity ratio is 20% or more, the control means  124  turns ON the display window(s)  121  according to the residual capacity ratio, followed by returning to the monitoring of the ON/OFF states of the LEDs (step S 4 ). 
     When it is found in step S 1  that the LED(s) at the display window(s)  121  is ON, the control means  124  determines whether or not the residual capacity display switch  122  has been depressed for 0.5 second or less (step S 5 ). Then, where the time for which the residual capacity display switch  122  has been depressed is 0.5 second or less, the control means  124  determines whether or not the LED ON condition has continued for 1 second (step S 6 ). Where the LED ON condition has not continued for 1 second, the control means  124  maintain the ON state of the LED(s), and where the LED ON condition has continued for 1 second or above, the control means  124  turns OFF the LED(s), followed by returning to the monitoring of the ON/OFF states of the LEDs (step S 7 ). 
     When it is found in step S 5  that the residual capacity display switch  122  has been depressed for more than 0.5 second, the control means  124  determines whether or not the LED ON condition at the display window(s)  121  has continued for 5 second (step S 8 ). Where the LED ON condition has not continued for 5 second, the control means  124  maintains the LED ON condition, and where the LED ON condition has continued for 5 second, the control means  124  turns OFF the LED(s), followed by returning to the monitoring of the ON/OFF states of the LEDs (step S 9 ). 
     Thus, in the residual capacity display unit  120 , the ON time of the display window(s)  121  differs depending on the time for which the residual capacity display switch  122  is depressed. For example, in the case of sequentially checking the residual battery capacity ratios of a plurality of spare battery packs  1 , it takes much time to check the residual battery capacity ratios one by one. In such a case, therefore, the plurality of spare battery packs  1  may be arranged in a row, and the residual capacity display switch  122  may sequentially be depressed for a long time so as to turn ON the display window(s)  121  for 5 second or more, whereby the residual capacity ratios can be confirmed efficiently. 
     Incidentally, the time for which the residual capacity display switch  122  is depressed for the purpose of prolonging the ON time of the display window(s)  121  is not limited to 0.5 second but may be changed, as required. In addition, the ON time of the display window(s)  121  prolonged when the residual capacity display switch  122  is depressed for a long time is not limited to 5 second but may be changed, as required. 
     Besides, the change made in the ON/OFF state of the display window(s)  121  when the residual capacity display switch  122  is depressed for a long time is not limited to the prolonging of the ON time but may, for example, be an increase in the luminance of the LED(s) in the display window(s)  121 . When the luminance of the LED(s) in the display window(s)  121  is enhanced, it is possible to enhance the visibility of the display windows  121  in a light environment, such as outdoors in daytime. 
     Further, the change made in the ON/OFF state of the display window(s)  121  when the residual capacity display switch  122  is depressed for a long time is not limited to the prolonging of the ON time but may, for example, be blinking of the LED(s) in the display window(s)  121 , whereby it is also made possible to enhance the visibility of the display windows  121 . In addition, if the blinking is adopted when the ON time is prolonged, the power consumption for emitting light can be suppressed. Incidentally, the control means  124  may blink the LEDs in the display windows  121  also when the residual capacity display switch  122  is not depressed for a long time, which also enhances the visibility of the display windows  121 . 
     Besides, the operation of the residual capacity display unit  120  is not limited to the four-stage display of the display windows  121  but may be set otherwise, as required. Furthermore, where the residual battery capacity is less than 20%, the color(s) of the LED(s) in the ON state or blinking state may be changed so as to make a display in four stages (20 to 15%, 15 to 10%, 10 to 5%, and below 5%). 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.