Battery pack

A battery assembly of a battery pack has a structure in which a substrate holder abuts on a side surface of a cell with a protecting circuit being held. The substrate holder includes a first side plate having a circuit part fitted part in which a circuit element of the protecting circuit is fitted and a second side plate along which a first lead is situated. Above the first side plate, a brim is provided that protrudes by an amount substantially equal to the sum of the thicknesses of the substrate and the circuit element, that is, the thickness of the protecting circuit substrate. Above the second side plate, a brim is provided that protrudes by an amount greater than the thickness of the first lead.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2006-152616 filed in Japan on May 31, 2006, the entire contents of which are hereby incorporated by reference.

BACKGROUND

The present aspect relates to a chargeable and dischargeable non-aqueous electrolyte secondary battery used mainly as a power source of mobile electronic equipment such as a video camera, a mobile computer, and a mobile telephone, and more specifically, to a battery pack in which a lithium-ion secondary battery or the like is accommodated in an insulating case.

2. Description of Related Art

In recent years, a chargeable and dischargeable rectangular parallelepiped non-aqueous electrolyte secondary battery such as a lithium-ion secondary battery has been mainly used as a power source of rapidly proliferating mobile electronic equipment such as a video camera, a mobile computer, and a mobile telephone. The lithium-ion secondary battery has a structure in which an electrode assembly comprising a positive electrode and a negative electrode wound via a separator is accommodated in a rectangular parallelepiped case made of aluminum or an aluminum alloy.

A protecting circuit substrate that controls the battery voltage to prevent overcharge and over-discharge is disposed on one side surface of the lithium-ion secondary battery (unit cell) to form a battery assembly. The battery assembly is accommodated in an insulating case made of, for example, a synthetic resin to form a battery pack, and the battery pack is attached to electronic equipment. The protecting circuit substrate and the cell are electrically connected together by a lead plate for connection.

Japanese Patent Application Laid-Open No. 2005-190852 discloses a battery pack assembled by holding a cell in an upper case and a lower case each having the shape of a box with an opening on one surface thereof, which are prepared by splitting a case parallel to a flat surface portion of a battery assembly having the shape of a square flat plate into an upper part and a lower part, and then joining the cases by a method such as ultrasonic welding.

Japanese Patent Application Laid-Open No. 2005-100689 discloses a battery pack in which the undersurfaces of the upper case and the lower case are opened to form picture-frame-like upper and lower frames and after these frames are combined together, a label is wound.

Japanese Patent Application Laid-Open No. 2005-190956 discloses a battery pack in which the undersurface of the case is opened to form a picture-frame-like lower frame and after the lower frame is combined with the upper case, a label is wound.

Japanese Patent Application Laid-Open No. 2005-135770 discloses a battery pack in which an outer frame covering the side surfaces of the battery assembly is separated vertically to the plane surface of the battery assembly into U-shaped right and left frames and after these frames are fitted on the battery assembly, a label is wound. This patent application publication also discloses a battery pack in which the battery assembly is accommodated in a box-shaped case having an opening on one surface thereof and after a sheet cover is placed on the opened surface of the battery assembly, a label is wound.

Japanese Patent Application Laid-Open No. 2005-158452 discloses a battery pack in which a substrate accommodating part for accommodating a protecting circuit substrate is provided on a side plate of a rectangular frame where an external output terminal exposing window is provided.

Japanese Patent Application Laid-Open No. 2006-164559 discloses a battery pack having a case in which a rectangular frame surrounding the periphery of a battery assembly in which a protecting circuit substrate is disposed on one end surface of the cell is formed integrally with a rectangular plate covering the lower surface of the battery assembly, the frame on the side of the end surface serves as a coupling frame that causes the output terminal to be exposed, and the substrate accommodating part in which the protecting circuit substrate is fitted is provided on the coupling frame.

In the battery packs of Japanese Patent Application Laid-Opens Nos. 2005-190852, 2005-100689, 2005-190956, and 2005-135770, since a plurality of cases or frames are assembled or a box-shaped case and a sheet cover are combined together, the number of components is large and the structure is complicated. In addition, the number of assembly man-hours is large and the assembly process is complicated.

In the battery back of Japanese Patent Application Laid-Open No. 2005-135770, if the sheet cover is not accurately pasted to the battery assembly, it can occur that the sheet cover overlaps the side plate of the case or a large clearance is formed between the sheet cover and the case and this causes the inside of the battery pack to be exposed. For this reason, the sheet cover requires extremely high dimensional accuracy, and its pasting is cumbersome.

In the battery packs of Japanese Patent Application Laid-Opens Nos. 2005-158452 and 2006-164559, the substrate accommodating part is provided on the integrally formed outer frame or case in order to solve the problems of the battery packs of Japanese Patent Application Laid-Opens Nos. 2005-190852, 2005-100689, 2005-190956, and 2005-135770, and the number of assembly man-hours can be reduced. Although the outer frame or the case is normally formed by molding plastic with a specifically designed mold, the substrate accommodating part has a structure that cannot be taken out by opening the mold, that is, a so-called “undercut” structure, so that the mold structure for mold release is complicated and this increases the cost of the mold. In addition, since the degree of molding difficulty is high, the yields of components are poor.

SUMMARY

The present aspect has been made with the aim of solving the above problem, and it is an object of the present aspect to provide a battery pack having a simple structure in which a substrate holder is provided that supports a protecting circuit substrate longitudinally disposed on a side surface of a cell and has, on a side plate, a brim protruding outward by an amount not less than the thickness of the protecting circuit substrate or a brim protruding outward by an amount not less than the thickness of a lead plate and a battery assembly is accommodated in a case having an opening on one side, so that the number of components and the number of assembly man-hours can be reduced, the cost of the mold can be reduced since the case has no undercut part in the mold structure, and the protecting circuit substrate can be protected by filling the clearance between the battery assembly and the case with the brim to thereby prevent the exposure of the inside.

Another object of the present aspect is to provide a battery pack in which by a simple structure in which a substrate holder is provided that supports a protecting circuit substrate laterally disposed on a side surface of a cell and has, on a side plate, a brim protruding outward by an amount not less than the protruding amount of the protecting circuit substrate or a brim protruding outward by an amount not less than the thickness of a lead plate and a battery assembly is accommodated in a case having an opening on one side thereof, so that the number of components and the number of assembly man-hours can be reduced, the cost of the mold can be reduced since the case has no undercut part in the mold structure, and the protecting circuit substrate can be protected by filling the clearance between the battery assembly and the case with the brim to thereby prevent the exposure of the inside.

Another object of the present aspect is to provide a battery pack in which the brim has a protruding part protruding further outward and the case has a concave in which the protruding part is fitted, in an opening-side edge of the side plate opposed to the brim, so that the brim can be more stably held by the case by fitting the protruding part in the concave, and the exposure of the inside can be more reliably prevented.

Another object of the present aspect is to provide a battery pack in which since a protecting element supported by the substrate holder is provided and the brim has a width not less than the thickness of the protecting element, so that the protecting element can be prevented from being exposed and be protected.

A battery pack according to a first aspect is provided with:

a battery assembly including:a cell having a rectangular parallelepiped form including two parallel planes and four side surfaces, and having a protruding electrode on one of the side surfaces;a protecting circuit substrate having an external output terminal and a protecting circuit, and longitudinally disposed on the side surface of the cell;a first lead connecting one electrode of the protecting circuit substrate and the protruding electrode; anda second lead connecting the other electrode of the protecting circuit substrate and a side part of the cell, the side part being an electrode of a polarity different from a polarity of the protruding electrode;

a case having an opening on one face and accommodating the battery assembly; and

a label covering a part or all of the battery assembly and the case,

wherein a substrate holder is provided that includes:

a side plate interposed between the protecting circuit substrate and the side surface of the cell where the protecting circuit substrate is disposed; and

a brim provided to protrude outward from the side plate in a direction of a thickness of the protecting circuit substrate by an amount not less than the thickness of the protecting circuit substrate.

As described above, since the protecting circuit substrate is a substrate on which a circuit element is mounted, here, the thickness of the protecting circuit substrate is the sum of the thicknesses of the substrate and the circuit element.

Since the battery pack of the present aspect has a simple structure in which the battery assembly is accommodated in the box-shaped case unlike the conventional battery packs having the structure in which a plurality of cases or frames are combined or the structure in which a box-shaped case and a sheet cover are combined, and the substrate holder serves also as an insulator, the number of components and the number of assembly man-hours can be reduced. In addition, errors involved in assembly can be reduced.

Conventionally, after the battery assembly is accommodated in a box-shaped case, a sheet cover is placed on the surface of the battery assembly, on the side of the opening, to fill the clearance between the battery assembly and the case, thereby preventing the exposure of the inside and protecting the battery assembly. However, in the present aspect, since the brim can perform the function of the sheet cover, the sheet cover can be deleted. In addition, since the brim is integrally formed on the side plate of the substrate holder, unlike in the case where the sheet cover is placed, it is unnecessary to ensure the position accuracy.

Further, in the present aspect, the case is a simple box in which the side plates are provided around the plane and has no undercut part in the mold structure, the mold structure for component production is simple, and the cost of the mold can be reduced, so that the yields of components can be improved.

A battery pack according to a second aspect is provided with:

a battery assembly including:a cell having a rectangular parallelepiped form including two parallel planes and four side surfaces, and having a protruding electrode on one of the surfaces;a protecting circuit substrate having an external output terminal and a circuit element, and laterally disposed on the side surface of the cell;a first lead connecting one electrode of the protecting circuit substrate and the protruding electrode; anda second lead connecting the other electrode of the protecting circuit substrate and a side part of the cell, the side part being an electrode of a polarity different from a polarity of the protruding electrode;

a case having an opening on one face and accommodating the battery assembly; and

a label covering a part or all of the battery assembly and the case,

wherein a substrate holder is provided that includes:

a side plate interposed between the protecting circuit substrate and the side surface of the cell where the protecting circuit substrate is disposed;

a brim provided to protrude outward from the side plate in a protruding direction of the protecting circuit substrate by an amount not less than a protruding amount of the protecting circuit substrate; and

a rib provided to hang from the brim for inhibiting a movement of the protecting circuit substrate in a direction perpendicular to the plane thereof.

Conventionally, in the case of a battery pack where a battery assembly in which the protecting circuit substrate is laterally disposed on a side surface of the cell is accommodated in a box-shaped case, an upper case having a cover for covering the protecting circuit substrate is fitted on the case. In the present aspect, since the brim of the substrate holder performs the function of the upper case of filling the clearance between the battery assembly and the case to thereby prevent the exposure of the inside and protect the protecting circuit substrate, the upper case can be deleted.

Since the battery pack of the present aspect has a simple structure in which the battery assembly is accommodated in the box-shaped case, the number of components and the number of assembly man-hours can be reduced. In addition, errors involved in assembly can be reduced.

Further, in the present aspect, the mold of the case has no undercut part, the mold structure for component production is simple, and the cost of the mold can be reduced, so that the yields of components can be improved.

In a battery pack according to a third aspect, in the first or second aspect, the substrate holder has a side plate where the first lead and/or the second lead are independently disposed, and

a brim is provided to protrude outward from the side plate in a direction of a thickness of the first lead or the second lead by an amount not less than the thickness of the first lead or the second lead.

In the present aspect, the exposure of the inside can be prevented by filling the clearance between the case and the side surface of the battery assembly where the first lead and/or the second lead are disposed.

In a battery pack according to a fourth aspect, in any of the first to third aspects, a protruding part is provided to protrude outward from the brim and

the case has a concave in which the protruding part is fitted, in an opening-side edge of the side plate of the case, opposed to the brim.

In the present aspect, by fitting the protruding part in the concave, the brim can be more stably held by the case, so that the exposure of the inside of the battery pack can be prevented more reliably.

In a battery back according to a fifth aspect, in the third aspect, the side surface of the cell where the protruding electrode is provided and the side surface of the cell where the protecting circuit substrate is disposed are two adjoining side surfaces, and

the substrate holder abuts on the two side surfaces.

In the present aspect, since the brim is disposed in the part where there is clearance between the case and the battery assembly in the substrate holder in which the first lead is disposed on the side of the side surface of the cell where the protruding electrode is provided and on the side surface adjoining this, the protecting circuit substrate is disposed so as to be supported, the exposure of the inside of the battery pack is prevented and the battery assembly is protected with reliability.

In a battery pack according to a sixth aspect, in the third aspect, the side plate supports the first lead and a protecting element, and

the brim of the side plate protrudes by an amount not less than a sum of the thickness of the first lead and a thickness of the protecting element.

In a battery pack according to a seventh aspect, in the sixth aspect, the protecting element is a discrete element selected from a group comprising a PTC (positive temperature coefficient) element, a fuse, and a bimetallic switch or a composite element into which the discrete elements are combined.

In the sixth and seventy aspects, when the substrate holder supports the protecting element, the protecting element can be prevented from being exposed and be protected.

The above and further objects and features of the aspect will more fully be apparent from the following detailed description with accompanying drawings.

DETAILED DESCRIPTION

Hereinafter, the present aspect will be concretely described with reference to the drawings showing embodiments thereof.

First Embodiment

FIG. 1is a perspective view showing a battery pack1according to a first embodiment of the present aspect.FIG. 2is an exploded perspective view showing the battery pack1.FIG. 3is a perspective view showing a battery assembly2viewed from the rear side.FIG. 4is an exploded perspective view of the battery assembly2.

A cell21of the battery assembly2of the battery pack1is an square flat non-aqueous electrolyte secondary battery including a electrode assembly comprising a positive electrode and a negative electrode wound via a separator, specifically, a secondary battery such as a lithium-ion secondary battery, and the electrode assembly and non-aqueous substance are accommodated in a case made of aluminum or an aluminum alloy. A negative terminal21ais provided on one side surface of the cell21with an insulating plate (not shown), and a lead attachment plate21bis provided on the opposite side surface. The entire area of the part of the cell21other than the part where the negative terminal21ais provided is the positive electrode (terminal).

A double-faced fixing tape24is attached to a side surface of the cell21adjoining the side surface where the negative terminal21ais provided. A first side plate23aof a substrate holder (substrate supporter)23is attached to the fixing tape24in a condition of supporting a protecting circuit part22.

A circuit element22bis mounted on the surface of a substrate22aof the protecting circuit part22opposite to the cell21, and positive and negative external output terminals22cfor taking out power to the outside and taking in power from the outside for charging are formed by gold plating on the opposite side, that is, on the outer side.

A first lead22dconnects the electrode of the substrate22aand the negative terminal21a. A second lead22econnects the electrode of the substrate22aand a side surface of the cell21through the lead attachment plate21b.

FIG. 5is an enlarged perspective view showing the substrate holder23.FIG. 6is a cross-sectional view taken along the line A-A ofFIG. 1.FIG. 7is a cross-sectional view taken along the line B-B ofFIG. 1.

The substrate holder23has the first side plate23aand a second side plate23bperpendicularly connecting with the first side plate23aand abutting on the side surface of the cell21where the negative terminal21ais provided.

On the first side plate23a, a circuit element fitted part23cprotruding from the first side plate23ain a frame shape and in which the circuit element22bis fitted is provided, and on both sides thereof, substrate supporters23dsupporting both ends of the substrate22aare provided. At the end on the side of the second side plate23b, supporting plates23ealong which the first lead22dis supported are provided.

A brim23gprotruding from the first side plate23aby an amount substantially equal to the sum of the thicknesses of the substrate22aand the circuit element22b, that is, the thickness of the protecting circuit substrate is provided above the first side plate23aand on the upper side of the circuit element fitted part23c. In the present embodiment, the protruding amount of the brim23gis not less than the sum of the thicknesses of the substrate22aand the circuit element22b.

An exposure hole23ffor exposing the negative terminal21ais provided in a central part of the second side plate23b.

A brim23hprotruding by an amount greater than the thickness of the first lead22dis provided above the second side plate23b.

The circuit element22bof the protecting circuit part22is fitted in the circuit element fitted part23cof the first side plate23astructured as described above, the first lead22dis made to abut on the supporting plates23ewith both ends of the substrate22asupported by the substrate supporters23d, and the first side plate23ais adhered to the side surface of the cell21by the fixing tape24. Then, the first lead22dis situated along the second side plate23b, and the end thereof is spot-welded to the negative terminal21a. The second lead22eis situated along a side surface of the cell21adjoining the side surface on which the first side plate23babuts, and the end thereof is spot-welded to the lead attachment plate21b. In this manner, the protecting circuit part22is disposed on the cell21in a condition of being held by the substrate holder23, thereby forming the battery assembly2.

As shown inFIG. 2, the case3made of a synthetic resin includes a plane31and side plates32provided around the plane31. One of the side plates32has windows33for exposing the external output terminals22c.

A label4of an insulating sheet includes a rectangular plane part41and side parts42hanging down from the plane part41. One of the side parts42has a cut-out43for exposing the windows33.

The battery assembly2obtained as described above is accommodated in the case3with the external output terminals22cexposed through the windows33. Then, the plane part41of the label4is attached to the exposed surface of the battery assembly2, and with the windows33exposed through the cut-out43, the side parts42are attached along the side plates32of the case3. Thereby, the battery pack1is formed.

Since the battery pack of the present embodiment has a simple structure in which the battery assembly2is accommodated in the box-shaped case3unlike the conventional battery packs having the structure in which a plurality of cases or frames are combined or the structure in which a box-shaped case and a sheet cover are combined, the number of components and the number of assembly man-hours can be reduced. In addition, errors involved in assembly can be reduced.

Conventionally, after the battery assembly is accommodated in a box-shaped case, a sheet cover is placed on the surface, on the side of the opening, of the battery assembly to fill the clearance between the battery assembly and the case, thereby preventing the exposure of the inside and protecting the battery assembly. However, in the present embodiment, since the brims23gand23hcan perform the function of the sheet cover, the sheet cover can be deleted. In addition, unlike in the case where the sheet cover is placed, it is unnecessary to ensure the position accuracy.

Further, in the present embodiment, the case3is a simple box in which the side plates32are provided around the plane31and has no undercut part in the mold structure, the mold structure for component production is simple, and the cost of the mold can be reduced, so that the yields of components can be improved.

Second Embodiment

FIG. 8is a perspective view showing a battery assembly12of a battery pack11according to a second embodiment of the present aspect.FIG. 9is a cross-sectional view of the battery pack11taken along a plane passing through the terminal windows33and perpendicular to the side plate32of the case3where the terminal windows33are provided.FIG. 10is a cross-sectional view of the battery pack11taken along a plane parallel to the side plate32of the case3where the terminal windows33are provided. In these figures, the same parts as those ofFIGS. 3,5, and6are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

On a substrate holder23kof the present embodiment, to the outside of the brim23gprotruding by the amount substantially equal to the sum of the thicknesses of the substrate22aand the circuit element22b, a protruding part23ifurther protruding from the brim23gis provided. At the opening-side edge of the side plate32of the case3opposed to the brim23g, a concave32ain which the protruding part23iis fitted is provided.

To the outside of the brim23hprotruding by the amount greater than the thickness of the first lead22d, a protruding part23jfurther protruding from the brim23his provided. At the opening-side edge of the side plate32of the case3opposed to the brim23h, a concave32bin which the protruding part23jis fitted is provided.

In the present embodiment, by fitting the protruding part23iin the concave32aand fitting the protruding part23jin the concave32b, the brims23gand23hcan be more stably held by the case3, so that the exposure of the inside can be prevented with reliability.

Third Embodiment

FIG. 11is a perspective view showing a battery assembly14of a battery pack13according to a third embodiment of the present aspect.FIG. 12is a cross-sectional view of the battery pack13taken along a plane passing through a PTC element22fand perpendicular to the side plate32of the case3where the PTC element22fis disposed. In the figures, the same parts as those ofFIGS. 8 and 10are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

In a protecting circuit part22hof the present embodiment, the PTC element22fis connected to the end of the first lead22d. The PTC element22fis a protecting element that shuts off the circuit by becoming highly resistive in response to the temperature when, for example, the temperature of the cell21is increased abnormally. The PTC element22fis connected to the negative terminal21aby a third lead plate22g.

In a substrate holder23mof the present embodiment, like in the second embodiment, the protruding part23iis provided to protrude outward from the brim23g, and the protruding part23jis provided to protrude outward from the brim23h. The brim23hprotrudes by an amount substantially equal to the sum of the thicknesses of the PTC element22f, the first lead22d, and the third lead plate22g. The protruding part23jis fitted in the concave32bof the side plate32of the case3.

In the present embodiment, when the substrate holder23malso holds the PTC element22f, the PTC element22fcan be protected by preventing the exposure of the PTC element22fwith the brim23h. Since the protruding part23jis fitted in the concave32b, the brim23his stably held by the case3.

While the substrate holder23mholds the PTC element22fas the protecting element in the present embodiment, the present aspect is not limited thereto. The substrate holder23mmay hold a discrete element selected from a group comprising a PTC element, a fuse, and a bimetallic switch or a composite element into which the discrete elements are combined. In this case, it is necessary that the brim23hhas a width greater than the thickness of the protecting element, and when the lead plate is connected in the direction of the thickness of the protecting element, has a thickness not less than the sum of the thicknesses of the protecting element and the lead plate.

Fourth Embodiment

FIG. 13is an exploded perspective view showing a battery assembly15of a battery pack according to a fourth embodiment of the present aspect. In the figure, the same parts as those ofFIG. 4are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

A substrate holder23nof the present embodiment includes the first side plate23a, the second side plate23bconnected to one side of the first side plate23a, and a third side plate23pconnected to the other side of the first side plate23a. The third side plate23phas an exposure hole23qfor exposing the lead attachment plate21b. Although the second lead22eprotrudes by its thickness from the third side plate23pwhen spot-welded to the lead attachment plate21b, a brim23rhaving a width not less than the thickness of the second lead22eis provided above the third side plate23p.

Therefore, in the present embodiment, since the brims23g,23h, and23rare disposed in all the parts where there is clearance between the case3and the battery assembly15, the exposure of the inside of the battery pack is prevented and the battery assembly15is protected with reliability.

Fifth Embodiment

FIG. 14is a perspective view showing a battery assembly16of a battery pack according to a fifth embodiment of the present aspect.FIG. 15is an exploded perspective view showing the battery assembly16. In these figures, the same parts as those ofFIGS. 3 and 4are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

In the cell21of the battery assembly16, the lead attachment plate21bis provided at the end of the side surface where the negative terminal21ais provided. The fixing tape24has exposing holes24aand24bfor exposing the negative terminal21aand the lead attachment plate21b.

In the protecting circuit part22iof the present embodiment, the second lead22eis disposed on the rear side of the end of the substrate22aon the side where the external output terminals22care provided, and the first lead22dis disposed opposite to the circuit element22b.

A substrate holder23sof the present embodiment includes one side plate23awhich has the exposure holes23fand23qfor exposing the negative terminal21aand the lead attachment plate21b. The outside of the exposure hole23fis the circuit element fitted part23cin which the circuit element22band the first lead22dare fitted, and both sides thereof are the substrate supporters23dholding both ends of the substrate22a.

The side plate23afurther has the brim23gprotruding from the side plate23aand having a width not less than the sum of the thicknesses of the first lead22d, the circuit element22b, and the substrate22a.

In the present embodiment, the first lead22d, the second lead22e, the circuit element22b, and the substrate22adisposed on one side surface of the cell21and protruding from the side plate23acan be all protected by the brim23g.

Sixth Embodiment

FIG. 16is a perspective view showing a battery assembly17of a battery pack according to a sixth embodiment of the present aspect.FIG. 17is an exploded perspective view showing the battery assembly17. In the figures, the same parts as those ofFIGS. 3 and 4are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

In the battery assembly17of the present embodiment, the substrate22aof the protecting circuit part22jis laterally disposed on a side surface of the cell21.

The circuit element22bfor preventing overcharging or over-discharging is provided on the surface of the substrate22aof the protecting circuit part22j, positive and negative electrode plates (not shown) are connected to the circuit element22b, and the electrode plates are connected to the cell21through the first lead22dand the second lead22e, respectively. The external output terminals22cfor taking out power to the outside and taking in power from the outside for charging are formed by gold plating on the rear surface of the substrate22a.

A substrate holder23tof the present embodiment includes the first side plate23aand the second side plate23b. The brim23gis provided above the first side plate23a, and the brim23his provided above the second side plate23b.

The brim23ghas a width not less than the protruding amount of the substrate22aprotruding from the first side plate23awhen the protecting circuit part22jis fitted on the substrate holder23t. Ribs23uare provided to hang from the brim23g, thereby inhibiting a movement of the substrate22ain a direction perpendicular to the plane thereof.

The brim23hprotrudes by an amount substantially equal to the sum of the thicknesses of the PTC element22f, the first lead22d, and the third lead22g.

Conventionally, in the case of a battery pack where a battery assembly in which the substrate of the protecting circuit is laterally disposed on a side surface of the cell is accommodated in a box-shaped case, an upper case having a cover for covering the protecting circuit is fitted on the case. In the present embodiment, since the brim23gof the substrate holder23tperforms the function of the upper case of filling the clearance between the battery assembly17and the case3to thereby prevent the exposure of the inside and protect the substrate22aof the protecting circuit part22j, the upper case can be deleted.