Patent Publication Number: US-2021167454-A1

Title: Battery Pack and Propulsion Device

Description:
TECHNICAL FIELD 
     The present invention mainly relates to a battery pack which includes holders that hold a plurality of tubular batteries. 
     BACKGROUND ART 
     Conventionally, as disclosed in Patent Literature 1, a battery pack is known which includes a holder made of a thermoplastic resin that holds a plurality of batteries. The battery pack of Patent Literature 1 includes a holder that holds the batteries, and a waterproof bag that accommodates the holder. A potting resin is injected into the waterproof bag. Because the potting resin adheres to the surface of the batteries and the battery holder, the heat of the batteries can be efficiently released. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 6242799 B2 
     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     However, even though the potting resin is a paste or liquid form at the time of injection, it hardens after injection and loses its fluidity. Therefore, when a gas is generated from the batteries, the gas cannot be released, and it is difficult to suppress the increase in pressure due to this gas. 
     The present invention has been made in view of the above circumstances, and a primary object thereof is to provide a battery pack that, when a gas is generated from the batteries, is capable of suppressing the increase in pressure due to the gas. 
     Means for Solving the Problems 
     The problem to be solved by the present invention is as described above, and the means for solving the problem and the effect thereof will be described below. 
     According to a first aspect of the present invention, a battery pack having the following configuration is provided. That is to say, the battery pack includes a plurality of batteries, a plurality of holders, a storage bag, and a battery casing. The holders hold the plurality of batteries. The storage bag is a flexible bag-shaped member in the interior of which the holders holding the plurality of batteries are accommodated, and is filled with an insulating filler that is fluid and not solidified during use. The battery casing accommodates the storage bag in which the holders are accommodated. 
     As a result of the insulating fluid being a fluid, even when a gas is generated from the batteries, the gas can be moved through the insulating filler to reduce the pressure. Furthermore, because the insulating filler also enters between the batteries and the holders, the heat transfer between tubular batteries is promoted due to the increased adhesion between the batteries and the insulating filler. As a result, the temperature of the plurality of tubular batteries can be made more uniform. Moreover, as a result of the insulating filler being filled in a flexible bag-shaped member, it becomes easier to align the storage bag with the shape of the holders and the like, and therefore, it becomes possible to reduce the size of the battery pack, and to reduce the weight by reducing the amount of the insulating filler. 
     In the battery pack described above, it is preferable to include a discharge part that opens when a gas is generated from the batteries, and at least discharges the gas to the outside of the battery casing. 
     Consequently, even when a gas is generated from the batteries, it is possible to discharge the gas to the outside of the battery casing via the discharge part. 
     The battery pack mentioned above preferably has the following configuration. That is to say, the battery casing includes a case body and a lid portion. The case body has a cylindrical shape and has at least one end which is open. The lid portion closes the portion of the case body which is open. The space filled by the insulating filler is closed by the lid portion, and the discharge part is formed in the lid portion. 
     Consequently, the gas generated from the batteries can be discharged to the outside of the battery casing via the discharge part in the lid portion. Furthermore, compared to a case where discharge parts are individually provided in the storage bag and the battery casing, the structure for discharging the gas can be simplified. 
     The battery pack mentioned above preferably has the following configuration. That is to say, the battery pack includes a battery control unit that determines a state of the plurality of batteries based on a detection result of a sensor. The battery control unit is accommodated in the storage bag. 
     As a result, the battery control unit is waterproofed by the storage bag. Furthermore, when a harness is connected to the battery control unit, the harness is also waterproofed by the storage bag. 
     According to a second aspect of the present invention, a propulsion device having the following configuration is provided. That is to say, the propulsion device includes the battery pack described above, a drive source, and a propulsion unit. The drive source is driven by electric power supplied from the battery pack. The propulsion unit uses a drive force generated by the drive source to generate a propulsive force that moves a moving body. 
     Consequently, it is possible to realize a propulsion device having a configuration in which the temperature of a plurality of tubular batteries is made uniform, even in a wide operating temperature environment. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing a configuration of an electric sliding body provided with a propulsion device according to a first embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of a battery pack cut along a plane parallel to the axial direction. 
         FIG. 3  is a cross-sectional perspective view of the battery pack. 
         FIG. 4  is a perspective view showing the shape of the holders. 
         FIG. 5  is a side view of an all-terrain vehicle provided with a propulsion device according to a second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, a first embodiment of the present invention will be described with reference to the drawings.  FIG. 1  is a perspective view showing a configuration of an electric sliding body  1  provided with a propulsion device  13  according to the first embodiment. Furthermore, in the description below, front, rear, left, and right are defined assuming that the forward direction of the electric sliding body  1  is the front. The electric sliding body  1  shown in  FIG. 1  is a vehicle that slides on water by acquiring a thrust generated by electric power. As shown in  FIG. 1 , the electric sliding body  1  includes a surfboard  11 , a support column  12 , and a propulsion device  13 . 
     The surfboard  11  is a plate-shaped member having a flat upper surface. The surfboard  11  slides on water as a result of the propulsion device  13  generating a propulsive force while a person is on the upper surface of the surfboard  11 . In addition, another member that travels on water or underwater may be provided instead of the surfboard  11 . Furthermore, a support column  12  is connected to the lower surface of the surfboard  11 . The support column  12  downwardly extends from the lower surface of the surfboard  11 , and is connected to the upper surface of the propulsion device  13 . 
     The propulsion device  13  generates a propulsive force for propelling the surfboard  11 . The propulsion device  13  includes a head unit  20 , a battery pack  30 , and a propulsive force generation unit  90 . 
     The head unit  20  is a member that configures the front part of the propulsion device  13 . The head unit  20  has a shape in which the outer diameter decreases toward the front. A front foil  21  is connected to the head unit  20 . The front foil  21  is arranged so as to extend in the left-right direction from the head unit  20 . At the time of propulsion, the front foil  21  causes the electric sliding body  1  to generate a levitation force, and stabilizes the behavior of the electric sliding body  1 . 
     The battery pack  30  is a part that stores electric power used to generate a propulsive force. The battery pack  30  is detachably attached to the rear of the head unit  20 . The battery pack  30  includes a plurality of tubular batteries  34 . Further, the battery pack  30  is configured to be capable of transmitting electric power to the propulsive force generation unit  90 . Moreover, the battery pack  30  is configured so that the state of the tubular batteries  34  can be determined based on the voltage values of the tubular batteries  34 , the surrounding temperature, and the like. The detailed configuration of the battery pack  30  will be described later. 
     The propulsive force generation unit  90  is detachably attached to the rear of the battery pack  30 . In this manner, the battery pack  30  of the present embodiment is configured to be separable from both the head unit  20  and the propulsive force generation unit  90 . The propulsive force generation unit  90  includes a drive casing  91 , an inverter  92 , an electric motor (drive source)  93 , a screw (propulsion unit)  94 , and a rear foil  95 . 
     The inverter  92 , the electric motor  93 , and the screw  94  are arranged inside the drive casing  91 . The direct current supplied from the battery pack  30  is converted into an alternating current having a predetermined frequency by the inverter  92 , and supplied to the electric motor  93 . The electric motor  93  generates a drive force from the alternating current supplied from the inverter  92 , and rotates the screw  94 . The propulsive force generation unit  90  generates a propulsive force as a result of the above configuration. Furthermore, like the front foil  21 , the rear foil  95  causes the electric sliding body  1  to generate a levitation force, and stabilizes the behavior of the electric sliding body  1 . 
     Next, the configuration of the battery pack  30  will be described with reference to  FIG. 2  to  FIG. 4 .  FIG. 2  is a cross-sectional view of the battery pack  30  cut along a plane parallel to the axial direction.  FIG. 3  is a cross-sectional perspective view of the battery pack  30 .  FIG. 4  is a perspective view showing the shape of the holders  33 . Note that, in the description below, the axial direction of the battery casing  31  or the tubular batteries  34  or the like may be simply referred to as the “axial direction”. Furthermore, the direction perpendicular to the axial direction is sometimes referred to as the “radial direction”. 
     As shown in  FIG. 2 , the battery pack  30  includes a battery casing  31 , an external terminal  32 , holders  33 , tubular batteries  34 , conductive plates  35 , a closed part  36 , a board housing unit  37 , and a storage bag  38 . Moreover, the inside of the storage bag  38  is filled with an insulating filler (the details will be described later). 
     The battery casing  31  is a member for accommodating each of the parts constituting the battery pack  30 . The battery casing  31  includes a case body  41  and a lid portion  42 . The case body  41  has a cylindrical shape and has one axial direction end (on the head unit  20  side) which is open. The lid portion  42  is arranged inside the case body  41  in the radial direction so as to close the opening of the case body  41 . Furthermore, a first seal member  61  is arranged between the case body  41  and the lid portion  42 . The first seal member  61  is an O-ring or the like, and prevents the entry of water into the case body  41  from between the case body  41  and the lid portion  42 . Further, even if a tear occurs in the storage bag  38 , it is possible to prevent the insulating filler from flowing out to the outside of the battery casing  31 . The other axial direction end of the case body  41  is also open, and is closed by an external terminal  32  and a member or the like which holds the external terminal  32 . However, the case body  41  may have a configuration in which only one axial direction end is open. 
     In addition, the lid portion  42  is provided with a handle  42   a  and a discharge valve (discharge part)  42   b . The handle  42   a  is provided on the outside of the lid portion  42  in the axial direction. The handle  42   a  is a rod-shaped member that the user can hold by hand. Furthermore, as mentioned above, because the battery pack  30  is separable from the head unit  20  and the propulsive force generation unit  90 , the user is able to easily hold and carry the battery pack  30  after separation by using the handle  42   a . The discharge valve  42   b  is configured to open and allow a gas to pass through when a certain pressure level or higher is applied. The discharge valve  42   b , for example, is configured to irreversibly open by creation of a tear or the like when the pressure difference exceeds a threshold value. Note that, because the function of the battery pack  30  is stopped when a large amount of gas is generated from the tubular batteries  34 , the discharge valve  42   b  of the present embodiment has a configuration that irreversibly opens. However, the discharge valve  42   b  may use a valve having a configuration that opens when the pressure difference exceeds a threshold value, and closes again when the pressure difference becomes less than or equal to the threshold value. The discharge valve  42   b  is used to discharge the gas generated from the tubular batteries  34  to the outside of the battery pack  30  (the details will be described later). 
     The battery casing  31  is formed in a substantially cylindrical shape. The battery casing  31  of the present invention has a shape in which the length in the axial direction is shorter than the length in the radial direction (that is to say, a long and narrow shape). As a result of the battery casing  31  having such a cylindrical shape, the water pressure applied to the battery casing  31  becomes uniform, and therefore, a high-pressure resistance can be realized with a simple structure. 
     Furthermore, the battery casing  31  of the present embodiment constitutes the outer wall of the propulsion device  13 , and also constitutes the casing of the battery pack  30 . In other words, the battery casing  31  has both a function for protecting the inside from the external environment, such as water, and a function for accommodating and arranging the tubular batteries  34  and the like. Therefore, the space can be efficiently utilized compared to a configuration that includes two casings. 
     Moreover, the battery casing  31  of the present embodiment is not produced by joining two semi-cylindrical members, but is molded into a cylindrical shape from the beginning. Therefore, no joint marks or the like are formed on the outer peripheral surface of the battery casing  31 . Consequently, it is possible to prevent the entry of water from the outer peripheral surface with a simple configuration, without performing steps such as providing a sealing material on the joint portions. Furthermore, in the present embodiment, the battery pack  30  is produced by assembling the members to be placed inside the battery casing  31  in advance, and then inserting the assembly into the battery casing  31 . 
     The battery casing  31  may have a shape other than a cylindrical shape. Furthermore, the casing of the propulsion device  13  and the casing of the battery pack  30  may be separate members. Moreover, a configuration is possible in which the battery casing  31  is produced by joining a plurality of members. 
     The external terminal  32  is provided so as to project outward from the case body  41  on one axial direction side of the battery casing  31  (the propulsive force generation unit  90  side). The external terminal  32  can be connected to a charging terminal of a charging device, and a power supply terminal of the propulsive force generation unit  90 . The tubular batteries  34  can be charged by connecting the external terminal  32  to the charging terminal. Electric power can be supplied to the propulsive force generation unit  90  by connecting the external terminal  32  to the power supply terminal. Therefore, the battery pack  30  is provided with an insertion sensor (identifying means) for identifying, with respect to the external terminal  32 , whether the charging terminal or the power supply terminal is inserted into the external terminal  32 . 
     It is also possible to identify which terminal is connected without using an insertion sensor by, for example, the battery pack  30  communicating with the charging device or propulsive force generation unit  90  side. Furthermore, the external terminal  32  can be used for both charging the tubular batteries  34  and supplying power to the propulsive force generation unit  90 . Alternatively, the terminal for charging the tubular batteries  34  and the terminal for supplying power to the propulsive force generation unit  90  may be separate terminals. 
     As shown in  FIG. 2  and  FIG. 4 , a plurality of tubular batteries  34  are held by the holders  33 . The tubular batteries  34  are, for example, lithium ion batteries, and have a structure in which a positive electrode, a separator, a negative electrode, and the like are arranged inside a cylindrical outer can. The tubular batteries  34  are not limited to a cylindrical shape, and may have a tubular shape having a polygonal cross section. Further, the tubular batteries  34  may have a shape other than a tubular shape (for example, a cuboid shape). As a result of being held by the holders  33 , the orientations of the plurality of tubular batteries  34  are aligned in the axial direction, and they are also arranged side by side in the radial direction. 
     As shown in  FIG. 2  and  FIG. 4 , a plurality of holders  33  (four in this embodiment) is arranged side by side in the axial direction. The holders  33  are made of a material containing a flame-retardant resin as a main component. The holders  33  are formed with a plurality of tubular holding portions for inserting and holding the tubular batteries  34 . Therefore, in the present embodiment, the tubular batteries  34  are individually held. The holders  33  may be configured to hold a plurality of tubular batteries  34  in a bundle (that is to say, in a manner that causes the tubular batteries  34  to be in contact with each other). 
     The conductive plates  35  are plate-shaped members made of metal and having conductivity. A plurality of conductive plates  35  are arranged side by side in the radial direction at one axial direction end of a holder  33 , and a plurality of conductive plates  35  are also arranged side by side in the radial direction at the other axial direction end of the holder  33 . The terminals of the plurality of tubular batteries  34  are each connected to the conductive plates  35  by a method such as spot welding or ultrasonic welding. As a result, the conductive plates  35  connect in parallel a plurality of the tubular batteries  34  arranged side by side in the radial direction. 
     Furthermore, as described above, the conductive plates  35  are respectively arranged at both ends of the holders  33  in the axial direction. Therefore, two conductive plates  35  are adjacent to each other in the axial direction except at the axial direction ends. These two conductive plates  35  are connected to each other by a method such as spot welding or ultrasonic welding. As a result, the conductive plates  35  connect in series the tubular batteries  34  arranged in mutually adjacent holders  33 . 
     As shown in  FIG. 2 , the closed part  36  is arranged at the end portion on one side of the holders  33  (the head unit  20  side), which are arranged side by side in the axial direction. The closed part  36  closes one axial direction end of the holders  33 . Bolt insertion holes are formed in both the closed part  36  and the holders  33 . The closed part  36  and the holders  33  are joined by joining bolts  51 . Furthermore, the closed part  36  is also joined with the lid portion  42  by a separate bolt. 
     Furthermore, an injection hole  36   a  and a passage hole  36   b  are formed in the closed part  36 . The injection hole  36   a  is a hole for injecting the insulating filler into the storage bag  38 . The passage hole  36   b  is a hole for allowing the gas generated by the tubular batteries  34  to pass through. The passage hole  36   b  is formed in a position facing the discharge valve  42   b . The closed part  36  is configured so that the insulating filler inside does not flow out from parts other than the injection hole  36   a  and the passage hole  36   b . That is to say, a second seal member  62  is arranged between the closed part  36  and the lid portion  42 . The second seal member  62  is an O-ring or the like, and seals between the closed part  36  and the lid portion  42 . As a result, the insulating filler does not flow out from between the closed part  36  and the lid portion  42 . 
     With respect to the holders  33  arranged side by side in the axial direction, the board housing unit  37  is arranged at the end portion on the opposite side to the closed part  36 . The board housing unit  37  is configured so that the insulating filler inside is not discharged to the outside. Furthermore, a third seal member  63  is arranged between the board housing unit  37  and the case body  41 . The third seal member  63  is an O-ring or the like, and seals between the board housing unit  37  and the case body  41 . As a result, it is possible to prevent water from entering into the battery casing  31  from between the battery casing  31  and the board housing unit  37 . Further, even if a tear occurs in the storage bag  38 , it is possible to prevent the insulating filler from flowing out to the outside of the battery casing  31 . 
     A battery control board (battery control unit)  37   a  is arranged in the board housing unit  37 . The battery control board  37   a  performs processing for realizing a BMS (battery management system). Specifically, the tubular batteries  34  are equipped with a sensor that detects a voltage value and a temperature. The battery control board  37   a  acquires the detection results of the voltage sensor and the temperature sensor via a harness  52 . The harness  52  is connected to the battery control board  37   a  through, for example, a through hole formed in the holders  33 . Based on the detection results, the battery control board  37   a  performs a control that prevents overcharging when charging the tubular batteries  34 , and prevents overdischarging when power is supplied from the tubular batteries  34  to the propulsive force generation unit  90 . The battery control board  37   a  may be configured to acquire the voltages and temperatures mentioned above in a wireless fashion rather than via the harness  52 . 
     The storage bag  38  is a bag made of a material which is flexible, and does not allow the insulating filler filled inside to pass through. The holders  33  and the tubular batteries  34  are accommodated in the storage bag  38 . The storage bag  38  of the present embodiment has a cylindrical shape, with one end welded to the outer surface of the closed part  36 , and the other end welded to the outer surface of the board housing unit  37 . 
     As a result, the battery control board  37   a  is accommodated in the storage bag  38  in addition to the holders  33  and the tubular batteries  34 . The inside of the storage bag  38  has a waterproof structure so that the insulating filler does not flow out. Consequently, the holders  33 , the tubular batteries  34 , the battery control board  37   a , the harness  52  connected to these components, and the like, are also waterproofed with respect to outside water. Therefore, by covering many members with the storage bag  38 , it is possible to reduce the number of locations in which a waterproof structure is provided. 
     As mentioned above, the closed part  36  and the board housing unit  37  are configured so that the insulating filler filled inside is not discharged to the outside. In this manner, the closed part  36 , the board housing unit  37 , and the storage bag  38  form a space in which the holders  33  and the tubular batteries  34  are sealed. Therefore, the space in which the holders  33  and the tubular batteries  34  are arranged can be filled with the insulating filler. 
     Here, because the insulating filler does not have conductivity, unnecessary parts are not energized. Furthermore, because the insulating filler transfers heat more readily than air, even when only some of the tubular batteries  34  generate heat, the heat is easily released to the surroundings. As a result, the temperature of the plurality of tubular batteries  34  is made even more uniform. Moreover, because the insulating filler is fluid, it enters the gaps between the holders  33  and the tubular batteries  34 . Therefore, it sufficiently adheres to the tubular batteries  34 . As a result, heat dissipation of the tubular batteries  34  can be further promoted. 
     Further, because the holders  33  and the tubular batteries  34  are protected by both the storage bag  38  (and the insulating filler inside) and the battery casing  31 , a battery pack  30  having excellent impact resistance can be realized. 
     Also, the insulating filler of the present embodiment is a liquid or gel-like substance that does not solidify after filling (in other words, has a non-solidifying property). The insulating filler is, for example, a silicon-based liquid. Therefore, the insulating filler is fluid even when the battery pack  30  is used. Consequently, even when a gas is generated from the holders  33 , because the gas can be moved through the insulating filler, a local increase in the pressure can be avoided. 
     Specifically, when a gas is generated from the tubular batteries  34 , the gas flows to the surroundings through the insulating filler. Here, since the conductive plates  35  are arranged between the holders  33 , the holders  33  are arranged with a spacing. Therefore, irrespective of which tubular batteries  34  generate the gas, the gas does not fill a specific holder  33 , and the overall pressure inside the holders  33  is uniformly increased. As mentioned above, the passage hole  36   b  is formed in the closed part  36 , and the discharge valve  42   b  is provided at the end of the passage hole  36   b.    
     With this configuration, if a gas is generated from the tubular batteries  34  and the pressure near the discharge valve  42   b  exceeds a predetermined value, the discharge valve  42   b  opens. As a result, the insulating filler is discharged from the discharge valve  42   b , and the gas is also discharged from the discharge valve  42   b . Consequently, prior to the inside of the battery pack  30  reaching a high pressure due to the gas generated from the tubular batteries  34 , it is possible to discharge the gas to the outside of the battery pack  30  to reduce the pressure. 
     In the present embodiment, although the discharge valve (discharge part)  42   b  is provided in the lid portion  42 , a discharge part may be provided in the closed part  36 . Alternatively, a discharge part may be provided in the storage bag  38 . However, if a discharge part is provided in the storage bag  38 , a separate discharge part for discharging the gas discharged from the storage bag  38  to the outside of the battery pack  30  is required. 
     Next, a method of filling the insulating filler will be briefly described. Firstly, the holders  33  in which the tubular batteries  34  are arranged, the closed part  36 , and the board housing unit  37  are joined. Then, the joined members are covered with the cylindrical storage bag  38 . Next, one end of the storage bag  38  is welded to the outer surface of the closed part  36 , and the other end of the storage bag  38  is welded to the outer surface of the board housing unit  37 . Then, after suction of the air inside the storage bag  38  with a pump or the like, the insulating filler is injected from the injection hole  36   a . The injection hole  36   a  is closed after the insulating filler is sufficiently filled. The insulating filler is filled as a result of the above. 
     In the present embodiment, the storage bag  38  has a cylindrical shape, and the two openings are each welded to another member. The storage bag  38  may instead have one opening. Furthermore, instead of welding the storage bag  38  to other members, a process of closing the openings of the storage bag  38  may be performed. Furthermore, the storage bag  38  may be configured to not accommodate the board housing unit  37 . 
     Hereinafter, the present embodiment will be compared with a configuration in which the insulating filler is filled in a non-flexible storage component rather than the storage bag  38 . Because it is difficult or more costly to prepare such storage components with a shape that aligns with the holders  33  and the like, they have a relatively simple shape such as a cylindrical shape. Therefore, unnecessary gaps are formed between the storage component and the holders  33 . As a result, the size of the battery pack  30  increases, and the weight increases due to the increased amount of the insulating filler. In addition, the waterproof structure in such storage components for preventing the insulating filler from flowing out can become complicated. 
     In this regard, in the present embodiment, the flexible storage bag  38  is filled with an insulating filler. Therefore, the use of a storage bag  38  having an appropriate size enables the storage bag  38  to be aligned with the shape of the holders  33  or the like. As a result, the size of the battery pack  30  can be reduced, and the weight can be reduced by reducing the amount of the insulating filler. Further, because the inside of the storage bag  38  can be sealed by welding to other parts (specifically, the closed part  36  and the board housing unit  37 ), the waterproof structure can be simplified. 
     Next, a second embodiment will be described.  FIG. 5  is a side view of an all-terrain vehicle  100  provided with a propulsion device  101  according to the second embodiment. 
     The all-terrain vehicle  100  is a vehicle primarily for traveling on unpaved roads. The all-terrain vehicle  100  includes a propulsion device  101  and a vehicle body  105 . The propulsion device  101  includes a battery pack  102 , a hydraulic pump (drive source)  103 , and a crawler (propulsion unit)  104 . 
     The battery pack  102  of the second embodiment has the same configuration as in the first embodiment. The hydraulic pump  103  delivers hydraulic oil when electric power is supplied from the battery pack  102 . The crawler  104  moves the battery pack  102  by being driven by the hydraulic oil delivered by the hydraulic pump  103 . The crawler  104  may be driven by an electric motor rather than the hydraulic pump  103 . 
     As described above, the battery packs  30  and  102  of the embodiments above include a plurality of tubular batteries  34 , holders  33 , a storage bag  38 , and a battery casing  31 . The holders  33  hold a plurality of tubular batteries  34 . The storage bag  38  is a flexible bag-shaped member in the interior of which the holders  33  holding the plurality of tubular batteries  34  are accommodated, and is filled with an insulating filler that is fluid and not solidified during use. The battery casing  31  accommodates the storage bag  38  in which the holders  33  are accommodated. 
     As a result of the insulating fluid being a fluid, even when a gas is generated from the tubular batteries  34 , the gas can be moved through the insulating filler to reduce the pressure. Furthermore, because the insulating filler also enters between the tubular batteries  34  and the holders  33 , the heat transfer between tubular batteries  34  is promoted due to the increased adhesion between the tubular batteries  34  and the insulating filler. As a result, the temperature of the plurality of tubular batteries  34  can be made more uniform. Moreover, as a result of the insulating filler being filled in a flexible bag-shaped member, it becomes easier to align the storage bag  38  with the shape of the holders  33  and the like, and therefore, it becomes possible to reduce the size of the battery packs  30  and  102 , and to reduce the weight by reducing the amount of the insulating filler. 
     In the battery packs  30  and  102  of the embodiments above, a discharge valve  42   b  is included that opens when a gas is generated from the tubular batteries  34 , and at least discharges the gas to the outside of the battery casing  31 . 
     Consequently, even when a gas is generated from the tubular batteries  34 , it is possible to discharge the gas to the outside of the battery casing  31  via the discharge valve  42   b.    
     Furthermore, the battery packs  30  and  102  of the embodiments above include a battery casing  31 , a case body  41 , and a lid portion  42 . The case body  41  has a cylindrical shape and has at least one end which is open. The lid portion  42  closes the portion of the case body  41  which is open. The space filled by the insulating filler is closed by the lid portion  42 , and the discharge valve  42   b  is formed in the lid portion  42 . 
     Consequently, the gas generated from the tubular batteries  34  can be discharged to the outside of the battery casing  31  via the discharge valve  42   b  in the lid portion. Furthermore, compared to a case where discharge valves  42   b  are individually provided in the storage bag  38  and the battery casing  31 , the structure for discharging the gas can be simplified. 
     Moreover, the battery packs  30  and  102  of the embodiments above include a battery control board  37   a  that determines a state of the plurality of tubular batteries  34  based on a detection result of a sensor. The battery control board  37   a  is accommodated in the storage bag  38 . 
     As a result, in addition to the battery control board  37   a , a harness  52  between the tubular batteries  34  and the battery control board  37   a  is also waterproofed by the storage bag  38 . 
     Although the preferred embodiments of the present invention have been described above, the above configuration can, for example, be changed as follows. 
     Furthermore, the propulsion devices  13  and  101  of the embodiments above include battery packs  30  and  102 , an electric motor  93  (hydraulic pump  103 ) and a screw  94  (crawler  104 ). The electric motor  93  (hydraulic pump  103 ) is driven by the electric power supplied from the battery packs  30  and  102 . The screw  94  (crawler  104 ) uses the drive force generated by the electric motor  93  (hydraulic pump  103 ) to generate a propulsive force that moves the moving body (electric sliding body  1 , all-terrain vehicle  100 ). 
     Consequently, it is possible to realize propulsion devices  13  and  101  having a configuration in which the temperature of the plurality of tubular batteries  34  is made uniform even in a wide operating temperature environment. 
     In the embodiments described above, although a plurality of holders  33  are arranged along the axial direction, the number of holders  33  may be one, and the holders  33  may also be arranged along another direction. Furthermore, in the present embodiment, although a single storage bag  38  accommodates a plurality of holders  33 , a configuration which includes a plurality of storage bags  38  is also possible. In this case, for example, a configuration may be used in which a storage bag  38  is provided for each holder  33 . 
     The battery pack  30  of the embodiments above can also be used for supplying electric power to vehicles other than the electric sliding body  1  and the all-terrain vehicle  100 . Moreover, the battery pack  30  can also be used for supplying power to objects other than vehicles. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
         
           
               13 ,  101  Propulsion device 
               30 ,  102  Battery pack 
               31  Battery casing 
               32  External terminal 
               33  Holder 
               34  Tubular battery (battery) 
               35  Conductive plate 
               36  Closed part 
               37  Board housing unit 
               37   a  Battery control board (battery control unit) 
               38  Storage bag 
               41  Case body 
               42  Lid portion 
               42   a  Handle 
               42   b  Discharge valve (discharge unit)