Lead storage battery

A lead storage battery comprising a battery casing has a first case member (such as a tray) and a second case member (such as a cover) in a superposed relation. The tray has a protruding part for mounting one external terminal, and the cover has a protruding part for mounting the other external terminal. The tray and cover have recessed regions for receiving the protruding parts for mounting the external terminal of an opposing case member of the tray and the cover. The tray has a recessed region for holding a safety valve so that the safety valve is covered by the cover when the tray and the cover are superposed. A small hole is formed in the recessed region such that the small hole is connected with an interior of the battery casing.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a lead storage battery, and more 
specifically to a thin sealed type lead storage battery which is 
constituted by holding battery cells in a battery casing formed by 
superposing a pair of split cases. 
2. Description of the Prior Art 
Thin, sealed-type lead storage batteries of the above-mentioned type have 
been known as disclosed in, for example, Japanese Patent Laid-Open No. 
33828/1976, Japanese Utility Model Laid-Open No. 159162/1983, and Japanese 
Utility Model Laid-Open No. 157969/1983. Lead storage batteries disclosed 
in these publications are briefly described below. 
First, according to the lead storage battery disclosed in Japanese Patent 
Laid-Open No. 33828/1976, collectors and active material are arranged in a 
pair of split cases which are superposed under the condition in which 
separators are held in the active material. In this known lead storage 
battery, however, external terminals are protruded from the outer surfaces 
of split cases to take out the electric current from the collectors in the 
split cases to the units outside the battery. Therefore, the external 
terminals impose limitation on reducting the thickness of the battery, 
making it difficult to obtain batteries of desired thicknesses. In the 
lead storage batteries of this type, it is necessary to provide a safety 
valve for releasing gas. Thickness of the safety valve holding portion 
serves as another significant factor which imposes limitation on reducing 
the thickness of the batteries. 
In the lead storage battery disclosed in Japanese Utility Model Laid-Open 
No. 159162/1983, the positive and negative electrode formed by adhering 
electro-collecting boards onto one side of the active material layer are 
contained in a battery casing made of a resin via separators, holes are 
formed in the wall of the battery casing opposed to the electro-collecting 
boards, through holes are formed in end portions of the battery casing, 
rivet fittings that serve as external terminals of the positive and 
negative electrode are attached to the through holes, and portions of the 
electro-collecting boards facing the holes and rivet fittings are 
connected via lead wires that run on the surface of the battery casing. 
However, the thus constructed lead storage battery has problems as 
described below. First, lead wires are connected by soldering to the 
electro-collecting boards or the rivet fittings. Therefore, the 
electro-collecting boards, lead wires, rivet fittings and the battery 
casing are damaged by the heat of soldering. Further, holes of the battery 
casing from where the lead wires are taken out, are sealed with a 
thermosetting resin such as an epoxy resin or the like. However, the holes 
are formed so shallow that there is no space for charging the epoxy resin 
in amounts sufficient to accomplish complete sealing. Therefore, the 
electrolyte in the battery casing often leaks from the sealed portions. 
Moreover, the rivet fittings that serve as external terminals assume the 
shape of a rod, and it is difficult in manufacturing the batteries to 
always secure the rod-like rivet fittings perpendicular to the plane of 
the battery casing. If the rivet fittings are tilted even by the slightest 
angle, complete electric contact is not obtained relative to the receiving 
terminals on the side of the electric equipment. 
With the lead storage battery disclosed in Japanese Utility Model Laid-Open 
No. 157969/1983, electro-collecting boards composed of lead or a lead 
alloy are mounted with the battery casing, and the electrode plates 
consisting of synthetic resin nets carrying an active material are closely 
adhered onto the electro-collecting boards, to realize a laminated thin 
battery structure having a cross section consisting of battery casing, 
electro-collecting board, cathode layer, separator, positive electrode 
layer, electro-collecting board and battery casing. However, this lead 
storage battery has problems as described below. First, in the 
conventional batteries, the battery casing is warped by the contraction of 
resin after molding, marring the appearance, and causing the output of the 
battery casing to decrease. Therefore, discharge capacity of the battery 
decreases greatly through charge-discharge cycles of the battery, and the 
life of the battery is considerably shortened. Further, discharge capacity 
reduction varies greatly. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a thin storage battery, 
the thickness, or miniaturization of which is limited neither by the 
external terminals through which the electric current is taken out from 
the collectors provided in the split cases constituting a battery casing 
to the units outside the battery nor by the safety valve holding portion. 
Another object of the present invention is to provide a thin storage 
battery which facilitates securing the external terminals of the battery 
to the battery casing and connecting the external terminals to the 
electro-collecting boards. This arrangement improves the sealing function 
and property between the regions near the electro-collecting boards and 
the external terminals, and eliminates the probability of poorly mounting 
the external terminals and a poor electric contact relative to the 
receiving terminals of external equipment. 
A further object of the present invention is to increase the resistance of 
the battery casing to warping after molding, to increase the yield of the 
battery casings, to prevent the battery life from being shortened by the 
electrolyte permeating onto the surfaces of the electro-collecting boards 
on the side of the battery casing, and to reduce variance in the battery 
discharge capacity in the charge-discharge cycles. 
To achieve the above-mentioned objects, the present invention deals with a 
lead storage battery in which battery cells are contained in a battery 
casing formed by superposing a pair of split cases (i.e., a bottom tray 
and a cover), the improvement wherein the one split case is provided with 
a protruding portion for mounting one external terminal, the other split 
case is provided with a protruding portion for mounting the other external 
terminal. Each of these split cases is provided with a recessed portion 
into which will be introduced the protruding portion for mounting the 
external terminal of the opposing case when these split cases are 
superposed. In one split case, there is formed a recessed portion for 
holding a safety valve which will be covered by the other split case when 
the split cases are superposed. The recessed portion for holding the 
safety valve has a small hole which is formed in the inner wall thereof 
and is communicated with the interior of the battery casing. Being 
constructed as described above, the protruding portions for mounting the 
external terminals of the split cases and the recessed portions of the 
opposing cases offset the thickness relative to each other, enabling a 
very thin battery casing to be constructed. Moreover, the safety valve 
holding portion is formed by the superposition of the two split cases, 
making it possible to minimize the thickness of the safety valve holding 
portion. The battery can be made thinner without involvement of any 
limitation of the thickness of the external terminals or of the safety 
valve holding portion. Further, the protruded portions and recessed 
portions for mounting the external terminals also work as guide means for 
superposing the split cases. 
In a preferred embodiment of the present invention, a groove is formed 
between the safety valve holding portion and the outer wall of the one 
split case. In the other split case, there is formed a protrusion that 
fits the groove when the split cases are superposed. The groove and the 
protrusion serve as guide means when the split cases are to be superposed. 
In another preferred embodiment of the present invention, a small gap is 
maintained between the groove and the protrusion when the split cases are 
superposed, so that gas in the safety valve holding portion can be 
released. 
In a further preferred embodiment of the present invention, an opening is 
formed in the protruding portions for mounting external terminals, to 
stretch a current tab which electrically connects the battery cells in the 
battery casing to the external terminals. According to this construction, 
the external terminals can be easily attached as will be mentioned in a 
subsequent embodiment. 
In a still further preferred embodiment of the present invention, 
electro-collecting boards are provided in the battery casing, the 
electro-collecting boards having at the ends thereof tabs for taking out 
the electric current. The tabs for taking out the electric current face 
into the openings which are filled up with a thermosetting resin such as 
an epoxy resin. The external terminal is formed by folding a flat plate in 
nearly a U-shape, mounted on the protruded portion so as to cover the 
opening, and is electrically connected in the opening to the tab for 
taking out the electric current. With this construction, the 
electro-collecting boards can be electrically connected to the external 
terminals without thermally damaging the battery casing. Also, a space can 
be maintained for holding the resin in amounts sufficient to completely 
seal a portion between the external terminal and the tab for taking out 
the current that stretches from the interior of the battery casing. 
Moreover, since much thermosetting resin exists, it can be supplied in a 
measured amount to enhance the yield rate for sealing the batteries. 
Further, the external terminal can be mounted on the protruding region 
when the thermosetting resin is charged into the opening, thereby securing 
the external terminal and sealing the region between the interior of the 
battery casing and the external terminal in a single operation. 
In another preferred embodiment of the present invention, the external 
terminal is provided with a cutout piece which is in contact with the tab 
for taking out the electric current. The cutout piece and the tab for 
taking out the current are welded together by bringing welding rods of a 
resistance welder into contact with the electro-collecting board and with 
the external terminal and by permitting the electric current to flow 
therethrough. In this construction, the tab for taking out the current and 
the erect piece are connected in the thermosetting resin. Therefore, 
electrically connecting the external terminal to the electro-collecting 
board, fitting the external terminal to the protruding part, securing the 
external terminal, and sealing the region between the interior of the 
battery casing and the external terminal, can be performed in a single 
step. 
In another preferred embodiment of the present invention, the split case 
made of a synthetic resin is provided with electro-collecting boards in 
such a manner that the peripheries of the electro-collecting boards are 
molded in the split case. The peripheral ends of the electro-collecting 
boards are bent toward the inside of the battery casing. Being constructed 
as described above, the battery casing provide effective resistance 
against warping after the molding, thereby increasing the production 
efficiency or yield rate of the battery casing. This construction also 
prevents the battery life from being shortened by the electrolyte 
permeating onto the surfaces of the electro-collecting boards on the side 
of the battery casing, and effectively reduces variance in the battery 
discharge capacity in the charge-discharge cycles. By applying a 
water-repellent coating to the peripheries of the electro-collecting 
boards, the electrolyte is almost completely prevented from permeating, 
and the above-mentioned inconveniences resulting from the permeation of 
the electrolyte can be effectively eliminated. A water-repellent or a 
hydrophobic material is applied to desired portions. Any material can be 
used as the water-repellent or hydrophobic material, provided that it does 
not adversely affect the storage battery. An organic hydrophobic material 
can be used, such as fluorine-contained resin dispersion, silicone rubber, 
silicone oil, polybutene, or the like. 
The water-repellent or hydrophobic material can be adhered coating, 
printing or any other known technique.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiment 1 
A first embodiment of the present invention will be described below with 
reference to FIGS. 1 to 4, wherein split cases 1 and 2 (i.e. a tray and a 
cover for it) that constitute in combination a battery casing for a lead 
storage battery, and that are obtained by molding a suitable material such 
as ABS, AS or a polypropylene, or an impact styrol (impact-resistant 
resin) into a predetermined shape. A recessed portion 3 is formed in the 
tray 1 to hold battery cells. In the recessed portion 3 for holding the 
battery cells, there is contained, as a unitary structure, an 
electro-collecting board (not shown) consisting of a plate-like lead which 
has a predetermined thickness and which is obtained by punching. One 
surface of the electro-collecting board and the peripheral portions 
thereof are covered by the material forming the battery casing. A similar 
recessed portion 31 is also formed in the other split case, i.e. cover 2, 
to hold the battery cells. In the recessed portion 31, there is provided, 
as a unitary structure, an electro-collecting board (not shown) in the 
same manner as described above. The electro-collecting boards which are 
formed as a unitary structure in the tray 1 and the cover 2 exhibit 
reinforcing function. Therefore, thickness of the layers can be reduced in 
the portion where the electro-collecting boards come into contact with the 
tray 1 and the cover 2. 
A rectangular, framelike rib 4 is formed on the side walls of the recessed 
portion 3 for holding the battery cells. A frame-like groove 5 is formed 
between the frame-like rib 4 and the peripheral walls of the tray 1. 
A protruding portion 6 for mounting the external terminal is formed on one 
side of the tray 1 protruding beyond the level of opening thereof. A 
recessed portion 9 holds a safety valve (not shown), the recessed portion 
9 being formed at a central portion on one side of the tray 1. The 
interior of the battery casing is communicated with the recessed portion 3 
for holding the battery cell through a small hole 10 formed in the inner 
side wall of the battery casing. Further, a groove 11 is formed in the 
outer side wall of the battery casing. A recessed portion 12 is formed in 
one side of the tray 1. The recessed portion 9 for holding the safety 
valve is positioned between the recessed portion 12 and the protruding 
portion 6 for mounting the external terminal. When the tray 1 and the 
cover 2 are superposed, the recessed portion 9 for holding the safety 
valve is covered by the cover 2 to hold the safety valve therein. 
A frame-like rib 13 is formed on the cover 2 and will be fitted to the 
frame-like groove 5 of the tray 1. A frame-like groove 14 is formed inside 
the frame-like rib 13, and will be fitted to the frame-like rib 4 of the 
tray 1. A recessed region 15 is formed in the cover 2. When the tray 1 and 
the cover 2 are superposed, the protruding part 6 for mounting the 
external terminal of the tray 1 is inserted in the recessed portion 15. A 
protruding part 16 mounts the external terminal, and is formed on the 
cover 2. When the tray 1 and the cover 2 are superposed, the protruding 
part 16 is inserted in the recessed region 12 of the tray 1. A protrusion 
17 is formed on the cover 2. When the tray 1 and the cover 2 are 
superposed, the protrusion 17 is fitted into the groove 11 formed in the 
tray 1. 
Openings 18, 19 are formed in the protruding portions 6, 16 for mounting 
the external terminals, and top plates 20, 21 are formed at positions 
slightly depressed from the outer surface of the battery casing. The top 
plates 20, 21 serve to keep spaces 22, 23 which correspond to the 
thickness of the external terminals 7, 8. 
The external terminals 7, 8 are folded in a U-shape, and are spot-welded, 
prior to superposing the tray 1 and the cover 2, to tabs (not shown) for 
taking out the electric current of the electro-collecting boards provided 
in the recessed portions 3, 31 for holding the battery cells in the casing 
1, 2. The external terminals 7, 8 are then buried in the spaces 22, 23 and 
are secured therein to close the openings 18, 19 as shown in FIG. 4. 
Described below is how to assemble the lead storage battery according to 
the first embodiment of the invention. 
First, a slurry kneaded material (not shown) composed of an active 
substance is poured onto surfaces of the electro-collecting boards (not 
shown) which are disposed in the battery casing of the tray 1 and the 
cover 2. The slurry kneaded material is then dried to form electrode 
plates on the surfaces of the electro-collecting boards. Then, a separator 
(not shown) consisting mainly of a glass fiber is placed on the upper 
surface of the electrode in the recessed region 3 for holding the battery 
cells of the tray 1, and an electrolyte of sulfuric acid is poured onto 
the separator. A tubular safety valve (not shown) made of rubber is 
inserted in the recessed region 9 for holding the safety valve of the tray 
1. Then the tray 1 and the cover 2 are superposed. The protruding parts 6, 
16 for mounting external terminals formed on the split cases (tray and 
cover) 2 are fitted into the recessed regions 15, 12 of the opposing cases 
relative to each other, and the protrusion 17 formed on the cover 2 is 
fitted to the groove 11 formed in the recessed region 9 for holding the 
safety valve of the tray 1. The thus established engagement serves as 
guide means for superposing the tray 1 and the cover 2, and helps 
temporarily maintain the tray 1 and the cover 2 in the superposed 
relation. When the tray 1 and the cover 2 are superposed, the frame-like 
rib 4 of the tray 1 is fitted to the frame-like groove 14, and the 
frame-like rib 13 of the cover 2 is fitted to the frame-like groove 5 of 
the tray 1. With the tray 1 and the cover 2 being superposed, the groove 
11 formed in the recessed portion 9 for holding the safety valve of the 
tray 1 is closed by the protrusion 17 of the cover 2. A small gap 24, 
however, is maintained between the groove 11 and the protrusion 17. 
Therefore, the gas produced by the electro-chemical reaction taking place 
in the battery casing is released out of the battery casing through small 
hole 10 in the tray 1, recessed region 9 for holding the safety valve, and 
gap 24. 
The battery is completely assembled if frame-like grooves 5, 14 and 
frame-like ribs 13, 4 of the tray 1 and the cover 2 are joined by 
ultrasonic welding. 
Embodiment 2 
Another embodiment of the present invention will be described below with 
reference to FIGS. 5 to 10. Split cases (tray and cover) that 41, 42 are 
obtained by molding a synthetic resin such as ABS, polypropylene or the 
like into a desired shape, and together constitute the battery casing. 
Electro-collecting boards 43, 44 are made of lead or a lead alloy, and are 
arranged on the inner surfaces of the split cases 41, 42 with their 
peripheral portions being molded as a unitary structure. Electrode plates 
45, 46 are closely adhered onto the surfaces of the electro-collecting 
boards 43, 44. A separator 47 is held between the electrode plates 45 and 
46 by a predetermined pressure. 
A recessed region 48 for mounting the external terminal is formed in an end 
of the tray 41. The recessed region 48 is formed from the upper surface to 
the side surface of the tray 41, and has an opening 49 which is formed in 
the side surfaces thereof and which is communicated with the interior of 
the tray 41. An external terminal 50 is obtained by folding nearly in a 
U-shape a flat plate which consists of an electrically conductive metal 
and which has a short strip 50a at a peripheral portion thereof. The 
external terminal 50 is secured in the recessed region 48 and is closely 
adhered thereto. A tab 43a for taking out the electric current stretches 
from an end of the electro-collecting board 43, and is long enough to be 
exposed out of the tray 1 penetrating through the opening 49. An epoxy 
resin 53 is filled in the recessed region 48 for mounting the external 
terminal 50, and effects the sealing so that the electrolyte in the 
battery casing will not leak therethrough. 
Described below is a procedure for mounting the external terminal on the 
lead storage battery according to the second embodiment of the invention. 
First, an end of the current take-out tabe 43a exposed to the outside 
through the opening 49 of the split case 41 is spot-welded by welding rods 
55, 56 onto the short strip 50a of the external terminal 50 as shown in 
FIG. 7A. The short strip 50a is then folded toward the inside of the 
external terminal 50 as shown in FIG. 7B, so that the current take-out tab 
43a is held between the short strip 50a and the external terminal 50. The 
epoxy resin 53 is charged into the recessed region 48 for mounting the 
external terminal of tray 41 and into the opening 49. The external 
terminal 50 is fitted into the recessed region 48 before the epoxy resin 
is hardened, thereby attaching the external terminal 50 thereto. A groove 
54 has been formed in the opening 49 of the tray 41 as shown in FIGS. 8, 
9, and a part of the external terminal 50 is inserted in the groove 54 so 
as not to escape therefrom. When the external terminal 50 is fitted as 
described above, the tab 43a for taking out the current assumes the folded 
state in the epoxy resin 53 as shown in FIG. 10. After the epoxy resin 53 
is set, therefore, the tab 43a for taking out the current is reliably 
secured to prevent a positional deviation thereof. 
Embodiment 3 
A third embodiment of the present invention will be described below with 
reference to FIGS. 11 to 16. 
In these drawings, a tray 61 and a cover 62, respectively, are obtained by 
molding a synthetic resin such as ABS or polypropylene into desired 
shapes. Electro-collecting boards 63, 64 consist of lead or a lead alloy, 
and are arranged on the inner surfaces of the tray 61 and the cover 62 
with their peripheral regions being molded. Electrode plates 65, 66 are 
arranged and firmly adhered onto the surfaces of the electro-collecting 
boards 63, 64. A separator 67 is inserted and pressed between the 
electrode plates 64 and 66 by a predetermined pressure. 
A recessed region 68 for mounting the external terminal is formed in one 
end of the tray 61. The recessed region 68 is formed from the upper 
surface to the side surface of the tray 61, and has an opening 69 that is 
formed in a region in the side surface thereof and that is communicated 
with the interior of the tray 61. An external terminal 70 is obtained by 
folding nearly in a U-shape a flat plate which consists of an electrically 
conductive metal and which has a cutout piece 70a formed at an end 
thereof. The external terminal 70 is secured in the recessed portion 68 
being closely adhered thereto. A tab 63a for taking out the electric 
current is formed at an end of the electro-collecting board 63 and is 
placed in the opening 69 in a folded manner. An epoxy resin 73 is filled 
in a space confined in the recessed portion 68 for mounting the external 
terminal 70, and effects sealing so that the electrolyte in the battery 
casing will not leak therethrough. 
Described below is a procedure for mounting the external terminal on the 
lead storage battery according to the third embodiment of the invention. 
First, the epoxy resin 73 is filled up in a sufficient amount around the 
current take-out tab 63a disposed in the opening 69 of the tray 61, and 
the external terminal 70 is fitted into the recessed portion 68 such that 
an end of the cutout piece 70a contacts the current takeout tab 63a. A 
groove 74 has been formed in the opening 69 as shown in FIG. 13, and a 
portion of the external terminal is inserted in the groove 74 so as not to 
slip out therefrom. Next, the tray 61 is placed on a resistance welder, a 
welding rod 75 is brought into contact with the electro-collecting board 
63 arranged in the tray 61, and another welding rod 76 forming a pair with 
the welding rod 75 is brought into contact with the external terminal 70. 
In this case, the end of the cutout piece 70a is biased by the welding rod 
76 toward the tab for taking out the current. If the power source of the 
resistance welder 77 is turned on under this condition, electric current 
flows, in turn, through the circuit consisting of welding rod 75, 
electro-collecting board 63, current take-out tab 63a, cutout piece 70a, 
external terminal 70 and welding rod 76, whereby the end of the cutout 
piece 70a and the current take-out tab 63a are welded together. 
Embodiment 4 
A further embodiment of the present invention will be described below with 
reference to FIGS. 17 to 20. A slurry kneaded material 81 is composed of 
an active material that serves as a cathode after drying, and is prepared 
by putting into a vessel 75 parts by weight of lead monoxide, 25 parts by 
weight of trilead tetroxide, 0.2 parts by weight of hydroxypropyl 
cellulose and 24 parts by weight of water, and by mixing them together 
using a stirrer for about 5 minutes. An electro-collecting board 82 
consists of lead or a lead alloy which is formed by punching, maintaining 
a size of a unit electrode. The electro-collecting board 82 has a current 
take-out tab 82b formed as a unitary structure on one side in the 
lengthwise direction thereof, and which is applied with a silicone rubber 
84 on the peripheries thereof as shown in FIG. 17, except a portion of the 
shape and size (rectangular shape in this embodiment) where the cathode of 
a predetermined size will be formed. The electro-collecting board 82 which 
is coated with the silicone rubber 84 is fitted, as shown in FIG. 18, to a 
rectangular tray 85 by injection molding to obtain a product 86 of a 
unitary structure, the end 82a at the periphery of the electro-collecting 
board 82 being bent toward the slurry kneaded material 81 as shown in FIG. 
20, and the rectangular tray 85 being obtained by injection-molding a 
synthetic resin. 
Water is poured on the upper surface of the electro-collecting board 82 of 
the thus obtained unitary product 86, and is then vacuumed off, or 
otherwise, the unitary product 86 is wholly submerged in water and is 
taken out. Then, the peripheral portions of the electro-collecting board 
82 coated with the silicone rubber 84 repel the water, and the portion not 
coated with the silicone rubber 84 other than the peripheral portions is 
wet with water. Therefore, the film of water is formed on the upper 
surface of the electro-collecting board 82 maintaining the shape of the 
positive electrode plate that was initially shaped by the silicone rubber 
84. 
The slurry kneaded material 81 is then poured on the film of water formed 
on the surface of the electro-collecting board 82. The slurry kneaded 
material 81 smoothly spreads out on the water film until it contacts the 
silicone rubber 84 along the periphery of the electro-collecting board 82. 
Then, the water contained in the slurry kneaded material 81 evaporates. 
Thus, there is obtained a cathode body having a three-layer construction 
consisting of tray, electro-collecting board, and positive electrode plate 
with the positive electrode plate adhering closely onto the surface of the 
electro-collecting board 82. 
A negative electrode body is also obtained in the same manner as described 
above but using a different active material that forms the slurry kneaded 
material, and a different additive in different amounts. The positive 
electrode body and the negative electrode body are then coupled via a 
separator (not shown), and the tray and the cover are joined by ultrasonic 
welding to complete the lead storage battery of the invention. 
With the end at the periphery of the electro-collecting board being folded 
as mentioned above, the probability of marring the appearance of the 
battery casing by the warping at the time of molding is reduced, and the 
production efficiency of the battery casings is increased by more than 
20%. This increase is attributed to the fact that the end at the periphery 
of the electro-collecting board which is folded helps increase the 
structural resistance to contraction of the resin in the battery casing. 
Described below with reference to FIGS. 21, 22 is the extent to which 
battery life can be extended by folding the peripheral end of the 
electro-collecting board and by applying a water-repellent coating 
composed of silicone rubber to the periphery of the electro-collecting 
board, as in the fourth embodiment (FIGS. 17-20). 
FIG. 21 shows relations between the charge-discharge cycles and the battery 
discharge capacity. Conventional lead storage batteries in which the 
peripheral end of the electro-collecting board is not folded and in which 
the water-repellent coating composed of silicone rubber is not applied, 
exhibit battery discharge capacities that can be approximated by a curve 
A, and that vary greatly between the curve B and a curve C. In contrast, 
the lead storage batteries according to the invention, in which the 
peripheral end of the electro-collecting board is folded, exhibit battery 
discharge capacities that vary within a very narrow, limited range between 
curve B and curve C. Further, the lead storage batteries of the present 
invention in which the peripheral end of the electro-collecting board is 
folded and in which the water-repellent coating composed of silicone 
rubber is applied, exhibit battery discharge capacities that are 
represented by the curve C. 
FIG. 22 shows relations between the charge-discharge cycles and the 
reduction rate of battery weight. With conventional lead storage 
batteries, the reduction ratios of battery weight greatly vary between a 
folded line A and a straight line C. With the lead storage batteries in 
which the peripheral end of the electro-collecting board is folded, the 
reduction ratios of battery weight lie between a folded line B and the 
straight line C. With the lead storage batteries in which the peripheral 
end of the electro-collecting board is folded and the water-repellent 
composed of silicone rubber is applied, the reduction ratios of battery 
weight are represented by the straight line C. In FIG. 22, inclination of 
the folded lines A, B increases at boundaries X1, X2, presumably due to 
the fact that the electrolyte had infiltrated onto the surface of the 
electro-collecting board on the side of the battery casing in the battery 
cycles, and the sealing function of the battery is destroyed at the points 
X1, X2. To investigate it, the batteries were disassembled, and it was 
noticed that the batteries in which the electrolyte permeates in large 
amounts onto the surfaces of the electro-collecting board on the side of 
the battery casing, exhibit charge-discharge cycle characteristics that 
are close to the curve A or the folded line A in FIGS. 21, 22. A 
correlation was confirmed that variance in the battery discharge capacity 
increases in proportion to the amount of the electrolyte which permeates 
the electro-collecting board. 
According to the fourth embodiment of FIGS. 17-20, furthermore, 
distinguished functions and effects are obtained as described below owing 
to the combination of a water-repellent or hydrophobic coating applied to 
the peripheral portions of the electro-collecting board, the 
electrode-forming portion of the electro-collecting board which is wetted 
with water, and the slurry kneaded material of an active material poured 
on the surface of the electrode-forming portion. Namely, the kneaded 
slurry poured on the surface of the electro-collecting board comes into 
contact with water on the electro-collecting board and, at the same time, 
spreads horizontally to quickly form a plane surface. At the peripheries 
of the electro-collecting board, the kneaded slurry is repelled by the 
water-repellent or hydrophobic material, and is prevented from spreading 
any further. Consequently, there is formed a layer of active material in a 
shape surrounded by the water-repellent or hydrophobic material. It is 
evident that a layer of active material of any shape can be formed on any 
place on the surface of the electro-collecting board by simply pouring a 
slurry kneaded material thereon. Furthermore, even when the batteries 
constructed are very small, by employing electrodes of a size smaller than 
the inner diameter of the battery casings to avoid the probability of 
short-circuit around the electrodes, it is allowed to easily form in the 
central portions of the battery casings electrodes of a size which is 
smaller than the inner size of the battery casings. 
Whereas the invention has been disclosed with reference to a particular 
embodiment, the same is not to be considered as limited to this 
embodiment, but its scope extends to the obvious changes and modifications 
that will be evident to those skilled in the art.