an embodiment of the present invention will be explained below according to figures . the battery pack of the present invention is mainly attached to electric vehicles used outdoor , and its power is supplied to a driving motor . the present invention is used as a power source for , such as , an electric assist bicycle , an electric auto - bike , an electric wheelchair , an electric tricycle , an electric cart , or the like . however , the present invention is not limited to uses of the battery pack , and the battery pack is also used as power sources of various electric devices which are used outdoors , such as , the power tool , or power sources for a house combined with solar cells . battery pack 100 shown in fig1 of the present invention , is attached to an electric device body , and supplies power to the electric device body . in battery pack 100 used for this purpose , battery core pack 1 is inserted in waterproof bag 2 , and this waterproof bag 2 is stored in outer case 3 . in battery core pack 1 , a plurality of battery cells 11 are disposed in a fixed position by battery holder 12 . battery cell 11 is a cylindrical battery cell which has positive and negative electrode terminals at both ends . in battery holder 12 , the plurality of battery cells 11 are arranged in parallel each other , and electrode terminals at both ends of battery cells are disposed in the same plane , and then the plurality of battery cells 11 are arranged in a multi - stage multi - row arrangement . in battery cells 11 stored in battery holder 12 , adjacent battery cells 11 are connected in series , or series and parallel by connecting lead plates to the electrode terminals ( not shown ). battery cells 11 are rechargeable lithium ion secondary batteries , but are not limited to lithium ion secondary batteries , and then any secondary batteries such as nickel hydride batteries , nickel cadmium batteries can be applied to the battery cells further , in battery pack 100 of the embodiment , the battery cells are cylindrical battery cells , but are not limited to this , and then can be rectangular parallelepiped batteries ( prismatic batteries ) or flat batteries . in battery core pack 1 , the plurality of battery cells 11 are arranged at parallel postures , and then are stored in battery holder 12 . in battery core pack 1 shown in the sectional view of fig1 pieces of battery cells 11 are disposed at parallel postures each other in battery holder 12 . battery holder 12 has holding pipes 13 where battery cells 11 are respectively inserted , and then holding pipes 13 holds battery cells 11 in fixed positions . battery holder 12 is made of thermoplastic resin such as plastic of insulating material . this battery holder 12 are divided in two parts in the longitudinal direction of battery cell 11 . the pair of the parts in battery holder 12 are coupled each other in a state where both ends of battery cells 11 are inserted in battery holder 12 , and then dispose each of battery cells in fixed positions . battery holder 12 has exposing openings 14 which expose parts of the surfaces of the battery cells in a state where battery cells 11 are inserted in holding pipes 13 . thus , exposing openings 14 are opened along the axes direction of battery cells 11 . battery cells 11 held at the fixed positions by being inserted into holding pipes 13 of battery holder 12 , expose the surfaces of the battery cells through exposing openings 14 . the exposed surfaces of battery cells 11 closely contact potting resin 4 injected , heat of battery cell 11 is radiated through potting resin 4 by heat transmission . opening windows which expose the electrode terminals provided at both ends of battery cells 11 , are provided in battery holder 12 . the lead plates for connecting adjacent battery cells 11 in series , are welded to the electrode terminals which are exposed from the opening window . further , battery cells 11 are connected to circuit board 6 through the lead plates . circuit board 6 has a protection circuit of battery cells 11 , leds displaying the remaining capacity of battery cells 11 , or the like . in battery core pack 1 of fig1 , circuit board 6 is disposed above battery holder 12 . circuit board 6 is disposed at a fixed position by battery holder 12 holding . potting resin 4 is injected into waterproof bag 2 in which battery core pack 1 shown in fig1 is inserted . potting resin 4 is made of insulating plastic such as urethane resin , and closely contacts the surfaces of battery cells 11 , circuit board 6 , or mounted components 7 of circuit board 6 in a state of heat transmission , to absorb heat . then , it prevents temperature of battery cells 11 , circuit board 6 , or mounted components 7 from being increased . potting resin 4 is uncured pasty or liquid , and is injected into waterproof bag 2 . then , potting resin 4 flows into under circuit board 6 , and between battery cells 11 , and is cured or hardened . cured potting resin 4 closely contacts both surface of the front and back surfaces of circuit board 6 , mounted components 7 such as semiconductor components included by circuit board 6 , or the exposed surfaces of battery cells 11 . potting resin 4 closely contacting circuit board 6 , mounted components 7 , and battery cells 11 , can conduct heat from circuit board 6 , mounted components 7 , and battery cells 11 , to suppress temperature increases of them . mounted components 7 included by circuit board 6 are semiconductor components such as fets , diodes . heat generation from them is conducted to potting resin 4 . especially , potting resin 4 closely contacting the surfaces of battery cells 11 effectively absorbs heat energy generated by temporary discharge or charge with a large current , to suppress temperature increase . it is important that potting resin 4 closely contacts the surfaces of heat generation components such as battery cells 11 , mounted components 7 , or circuit board 6 . when potting resin 4 failed in closely contacting , the heat generation of the heat generation components cannot be effectively conducted and radiated . then the temperature of mounted component 7 increases largely , and a normal operation cannot be guaranteed . further , the failure of contacting potting resin 4 and the exposed surfaces of battery cells 11 makes the battery temperature increased , and it makes battery cells 11 degraded , and it makes the life of battery cells 11 shortened . additionally , in the battery pack where current of charge or discharge is restricted based on battery temperature , the restrictions of the current of charge or discharge are frequently carried out , and it also restricts the timings of charges or discharges with normal current . battery core pack 1 of fig1 has a characterized structure in order to make potting resin 4 flow into in an ideal state . in order to make potting resin 4 quickly flow into under circuit board 6 , battery holder 12 has injecting opening 15 next to the side of circuit board 6 for injecting potting resin 4 . battery holder 12 of fig1 has injecting openings 15 opening upward , next to both sides of circuit board 6 . further , in order to make potting resin 4 injected through injecting opening 15 flow into between circuit board 6 and battery cells 11 , that is , under circuit board 6 , battery holder 12 has inclined surface 16 of a downward slope . battery holder 12 of the figures has inclined surfaces 16 , next to both sides of circuit board 6 . inclined surfaces 16 are disposed so as to be inclined toward the center axis of circuit board 6 , and then it makes potting resin 4 injected through injecting openings 15 smoothly flow into under circuit board 6 . battery holder 12 of fig1 has inclined surfaces 16 , from both sides of circuit board 6 , to outside . accordingly , potting resin 4 flowing into along inclined surface 16 , after flowing into under circuit board 6 , flows along the upper surfaces of battery cells 11 , and flows into between battery cells 11 . battery cells 11 are disposed in a characterized arrangement such that potting resin 4 flowing along the upper surfaces of battery cells 11 is made flow into until the center axis of circuit board 6 more smoothly . namely , battery cells 11 which are disposed at the back surface of circuit board 6 , are arranged in a state or position inclined in a downward slope toward a flowing direction of potting resin 4 . potting resin 4 flows into at the back surface of circuit board 6 , flowing in the direction indicated with arrows of fig2 . battery core pack 1 of fig1 , has first to sixth rows from the right to left . in order that battery cells 11 are disposed in the state or position inclined in the downward slope toward the flowing direction of potting resin 4 , battery cells 11 are arranged in the following way . battery cell 1 of the first row is higher than battery cell 1 of the second row , and battery cell 1 of the second row is higher than battery cell 1 of the third row . moreover , battery cells 11 are arranged in the following way . battery cell 1 of the sixth row is higher than battery cell 1 of the fifth row , and battery cell 1 of the fifth row is higher than battery cell 1 of the fourth row . as potting resin 4 flows from both sides of circuit board 6 to the center axis portion thereof , battery cells 11 are arranged in the state or position inclined in the downward slope from both sides of circuit board 6 to the center axis portion thereof . in battery core pack 1 above - mentioned , potting resin 4 flows into along inclined surface 16 of the downward slope , and then flows along the upper surfaces of battery cells 11 from inclined surface 16 into the center axis portion of the back surface of circuit board 6 . in this battery core pack 1 , potting resin 4 can surely flows even into the center axis portion of the back surface of circuit board 6 , where it is difficult that a potting resin flows . therefore , potting resin 4 can be injected into even the back surface of circuit board 6 , and then the surface of circuit board 6 closely contacts potting resin 4 in an ideal state . further , since potting resin 4 flows along the upper surface of battery cells 11 disposed in the downward slope from inclined surface 16 into the center axis portion , potting resin 4 can surely flows in close contact into even the upper surfaces of the battery cells 11 disposed under the center portion of the back surface of circuit board 6 , where it is difficult that a potting resin flows . potting resin 4 is also injected on the upper surface of circuit board 6 . on the upper surface of circuit board 6 , peripheral wall 17 is provided at the periphery of circuit board 6 . potting resin 4 are injected within peripheral wall 17 , and then potting resin 4 can closely contact the whole surface of the upper surface of circuit board 6 . in order that battery core pack 1 realizes the water seal structure excellent in a waterproof property , waterproof bag 2 stores battery core pack 1 . especially , in a state where battery core pack 1 is tentatively fixed in waterproof bag 2 , lead wires 5 extend from waterproof bag 2 . further , in a state where battery core pack 1 is disposed at a fixed position in waterproof bag 2 , potting resin 4 is injected . waterproof bag 8 is made of a flexible sheet having a bag shape . the flexible sheet is preferably a plastic sheet . the plastic sheet can be made of material , such as , polyimide ( pi ), polyethylene imide ( pei ), polyethylene terephthalate ( pet ), and the like . those plastic sheets are excellent in flexibility and heat - resisting property . in addition , those plastic sheets are not dissolved by an electrolyte which is exhausted at the time of opening a safety valve of the battery cell , and do not cause a chemical reaction . here , as the flexible sheet used for the waterproof , other plastic sheets other than the above can be used . waterproof bag 2 is formed in the bag shape as a preset shape , by processing flexible sheet material . waterproof bag 2 of fig2 , flexible sheet having a pipe shape is cut in a preset length , and the cut pipe shape is welded at one end thereof , namely , at the bottom end in the figure , to make the bag shape . since waterproof bag 2 is made by welding only the bottom end to make the bag shape , it can be effectively mass - produced . here , both sides of the bag can be surely coupled . otherwise , the waterproof bag may be made in the following way . two sheets of flexible sheets are disposed to face each other , and then are welded at both side edges and a bottom edge , to make a bag shape . in this waterproof bag , the two sheets of the flexible sheets are disposed to face each other , and this waterproof bag has the shape where both side edges and the bottom edge are connected . waterproof bag 2 is the bag shape having opening portion 20 at one end , and then battery core pack 1 is inserted and stored through opening portion 20 , and then lead wires 5 extends through opening portion 20 . lead wires 5 are connected to connectors ( not shown in the figures ) fixed to outer case 2 . such connectors have charge / discharge terminals or signal lines . accordingly , waterproof bag 2 stores battery core pack 1 , and lead wires 5 also extend outward from opening portion 20 of waterproof bag 2 . as shown in fig2 , lead wires 5 extend outward from opening portion 20 of waterproof bag 2 as a waterproof structure . waterproof bag 2 stores battery core pack 1 , and lead wires 5 extend outward . waterproof bag 1 of fig2 , has welding portions 22 which are welded by welding facing flexible sheets 21 at opening portion 20 in order to make opening portion 20 narrow . by welding portions 22 , opening portion 20 of waterproof bag 2 becomes narrower than a whole opening width ( w ), and it is used as inserting opening 23 for inserting battery core pack 1 . after providing welding portions 22 of waterproof bag 2 , battery core pack 1 is inserted in waterproof bag 2 by passing battery core pack 1 through inserting opening 23 . therefore , an opening width ( w ) of inserting opening 23 has a size through which battery core pack 1 can be inserted . here , in order that battery core pack 1 is able to be inserted through inserting opening 23 and is prevented from being protruded outside or going out at a carrying step or the like , the size of inserting opening 23 is a size through which battery core pack 1 is not able to be inserted in a direction or a posture where battery core pack 1 is stored in waterproof bag 2 and is able to be inserted in a direction which is changed from the stored direction . in a state where battery core pack 1 stays in waterproof bag 2 , potting resin 4 is injected into waterproof bag 2 , or opening portion 20 is made a waterproof structure . therefore , battery core pack 1 is made in a considerably bigger size than a size of battery core pack 1 , so as to effectively process at these steps . in order that potting resin 4 surely flows into necessary portions , a part of waterproof bag 2 is deformed , or battery core pack 1 is moved within waterproof bag 2 . waterproof bag 2 is bent so as to make opening portion 20 done in a waterproof processing , or waterproof bag 2 is made so as to be conveniently welded . thus , waterproof bag 2 is bigger than battery core pack 1 . the big waterproof bag 2 has the big whole opening width ( w ), battery core pack 1 is able to be easily inserted in waterproof bag 2 . however , there is a problem that battery core pack 1 protrudes or goes outside waterproof bag 2 . in order to resolve this problem , waterproof bag 2 of fig2 , includes welding portions 22 at opening portion 20 of waterproof bag 2 . thus , the opening width ( w ) of inserting opening 23 is smaller than the whole opening width ( w ). ideally , inserting opening 23 has a size through which battery core pack 1 is able to be passed in a specific posture , namely , only a specific inserting posture . for example , waterproof bag 2 which stores enlonged battery core pack 1 as shown in fig2 , has a size of inserting opening 23 through which battery core pack 1 is able to be inserted at only an inserting posture of the longitudinal direction of battery core pack 1 . since waterproof bag 2 of this inserting opening 23 can pass battery core pack 1 at only the inserting posture of the longitudinal direction of battery core pack 1 , it can ideally prevent battery core pack 1 from protruding or going outside . here , as waterproof bag 2 has the opening width ( w ) of inserting opening 23 smaller than the whole opening width ( w ), the opening width ( w ) of inserting opening 23 does not necessarily need to be limited to the size through which battery core pack 1 is able to be passed at the specific inserting posture thereof . it is a reason why waterproof bag 2 can suppress battery core pack 1 in protruding or going out , compared with waterproof bag 2 having no welding portion 22 , as waterproof bag 2 has the opening width ( w ) of inserting opening 23 smaller than the whole opening width ( w ). especially , the opening width ( w ) of inserting opening 23 is preferably 110 % or less of the value that the width and height of battery core pack 1 are added in the direction stored in waterproof bag 2 , and more preferably 105 % or less . it can prevent battery core pack 1 from protruding or going outside waterproof bag 2 , and can effectively assemble . waterproof bag 2 of fig2 has welding portions 22 at both sides of opening portion 20 , and has inserting opening 23 between welding portions 22 of both sides . welding portions 22 are respectively enlonged welding lines 22 a , and welding lines 22 a are inclined relative to an opening edge of opening portion 20 of waterproof bag 2 , in other words , to side edges of waterproof bag 2 . the length of each welding line 22 a is , for example , 2 cm or more , and 7 cm or less , and preferably 3 cm or more , and 6 cm or less , and more preferably approximately 5 cm . inclined welding lines 22 a are inclined so as to gradually increase the opening width toward opening portion 20 . in waterproof bag 2 having welding lines 22 a , battery core pack 1 can be smoothly inserted in waterproof bag 2 , and it can also surely prevents battery core pack 1 from protruding or going outside . it is a reason why battery core pack 1 is able to be inserted along welding lines 22 a . after battery core pack 1 is inserted in waterproof bag 2 , lead wires 5 are disposed along the inner sides of welding lines 22 a , and then inner welding lines 24 are provided along lead wires 5 as shown fig3 . inner welding lines 24 are provided such that facing flexible sheets 21 are welded in enlonged shapes in the same way as welding lines 22 a . inner welding lines 24 are provided at the inner sides of lead wires 5 , and then lead wires 5 are disposed between inner welding lines 24 and welding lines 22 a . inner welding lines 24 are provided in parallel with welding lines 22 a , and in a posture where those are inclined relative to the opening edge of opening portion 20 of waterproof bag 2 . a space or distance between inner welding line 24 and welding line 22 a is , for example , approximately 1 . 5 cm such that lead wire 5 is able to be disposed . this space is set as narrow as possible at the range where lead wire 5 is able to be disposed . further , waterproof bag 2 of fig3 , has waterproof line 25 for closing opening portion 20 in a waterproof structure . waterproof line 25 is provided such that facing flexible sheets 21 of opening portion 20 are welded in an enlonged shape in the same way as welding lines 22 a . this waterproof line 25 is provided in parallel with the opening edge of waterproof bag 2 . waterproof line 25 closes opening portion 20 of waterproof bag 2 in the waterproof structure , by connecting both ends of it to inner welding lines 24 of both sides . in waterproof bag 2 of fig3 , both ends of waterproof line 25 are connected to the inner side ends of inner welding lines 24 . waterproof bag 2 storing battery core pack 1 , is stored in outer case 3 . in waterproof bag 2 stored in outer case 3 , as shown by an alternate long and short dash line of fig3 , opening portion 20 is bent at bending line 26 , to make a whole size compact . lead wire 5 is disposed between inner welding line 24 and welding line 22 a , at a fixed position , and at a posture inclined relative to the opening edge of waterproof bag 2 . lead wire 5 is bent at a posture inclined relative to the bending line , and is curved in a predetermined radius of curvature , as shown by a chain line of fig3 in a state of bending opening portion 20 . namely , lead wire 5 can be bent without overlapping in the state where opening portion 20 of waterproof bag 2 is bent . additionally , lead wire 5 can be bent in the large radius of curvature . thus , bent opening portion 20 can be made thin , and also lead wire 5 can smoothly be being bent . further , a disconnection by curving lead wire 5 in a small radius of curvature can be prevented . battery pack 100 including a lot of battery cells 11 , has a large charge / discharge capacity , and a large output current . therefore , thick lead wire 5 having a large allowable current rate , is used . when thick lead wire 5 is bent and overlapped , it is made thick , and also it is difficult to bend it in a small radius of curvature . however , as shown in fig3 , lead wire 5 is disposed at the inclined posture , and then opening portion 20 of waterproof bag 2 is bent . therefore , lead wire 5 can be easily bent without overlapping lead wire 5 , in the large radius of curvature . further , opening portion 20 of waterproof bag 2 may be bent twofold or three fold to make it compact and to improve waterproof property , and then waterproof bag 2 is stored in outer case 3 . especially , in this battery pack 100 , since lead wire 5 is bent without overlapping , it is characterized that opening portion 20 of waterproof 2 is made thin , and is smoothly bent . in waterproof bag 2 of fig3 , lead wires 5 extend outside from both sides of opening portion 20 . for example , in this battery pack 100 , lead wire 5 of the output line from one side of waterproof bag 2 extends outside , and lead wire 5 of the signal line from the other side of waterproof bag 2 extends outside . as shown in the sectional view of fig1 , outer case 3 stores waterproof bag 2 which stores battery core pack 1 . outer case 3 has a box shape which is molded in a closing structure and is made of plastic . outer case 3 is divided into two parts of plastic which are molded . the two parts of outer case 3 are closed to store waterproof bag 2 inside . this outer case 3 has connectors ( not shown in the figures ) which have output terminals or signal terminals , and then lead wires 5 of battery core pack 1 are connected to the connectors . battery pack 100 above - mentioned , is manufactured by the following steps . 1 . in a welding step , welding lines 22 a are made by welding opening portion 20 of waterproof bag 2 in a long narrow shape ( an enlonged shape ). thus , inserting opening 23 of opening width ( w ) which is narrower than the whole opening width ( w ), is provided at opening portion 20 . otherwise , the welding step can be carried out when waterproof bag 2 is made . 2 . in an inserting step , battery core pack 1 is inserted in waterproof bag 2 . then , lead wires 5 are disposed along welding line 22 a , and inner welding lines 24 are made by welding opening portion 20 of waterproof bag 2 along lead wires 5 . inner welding lines 24 are provided at the inner sides of lead wires 5 . then , potting resin 4 is injected in waterproof bag 2 . potting resin 4 is injected inside through injecting opening 15 of battery holder 12 . potting resin 4 injected through injecting opening 15 , flows along inclined surface 16 into the back surface of circuit board 6 , and then flows along the upper surfaces of battery cells 11 disposed so as to be inclined in the downward slope in the flowing direction , and then potting resin 4 closely contacts the back surface of the circuit board 6 and battery cells 11 . in the present invention , potting resin 4 is injected at the upper surface of circuit board 6 . potting resin 4 closely contacts circuit board 6 , mounted components 7 , and battery cells 11 , namely , is injected in a thermal - coupling state . 3 . then , in a closing step , waterproof line 25 is made at waterproof bag 2 in which potting resin 4 is injected , and thus opening portion 20 is closed in the waterproof structure . waterproof line 25 is provided by connecting both ends of it to inner welding lines 24 . potting resin 4 is injected before making waterproof line 25 . instead , after making waterproof line 25 , potting resin 4 can be injected inside waterproof bag 2 by inserting a nozzle between welding lines 22 a and inner welding lines 24 . 4 . in an assembling step , waterproof bag 2 in which battery core pack 1 is stored and opening portion 20 is closed , is stored in outer case 3 , and then outer case 3 is closed . since battery core pack 1 has the waterproof structure by being inserted in waterproof bag 2 , it is not necessary that outer case 3 has a hermetical waterproof structure . here , needless to say , a more secure waterproof structure can be obtained by adopting a waterproof structure of outer case 3 . the battery pack of the present invention can be used in electric bicycles used outdoor , since it has a waterproof structure where a battery core pack is inserted in a waterproof bag .