For example, a lead storage battery has sulfuric acid stored therein as an electrolyte, and since the amount of such electrolyte has an important bearing on the performance of the storage battery and on the leakage of the electrolyte, it is necessary to keep the amount of the electrolyte under control so that its level in the battery casing is always in a given range. On the other hand, to monitor the charged condition, it is known to measure the specific gravity of the electrolyte.
One procedure for making it possible to monitor the electrolyte conditions, such as amount or specific gravity, from the outside, is to form a window in the lateral wall of the casing through which the interior of the casing can be seen, see for example, Japanese Utility Model Publication No. 233/1963. The simplest way to monitor the electrolyte surface level in the casing would be to make it possible to see the surface of the electrolyte directly through such window. In the case the electrolyte surface level is to be shown directly through the window, however, it is impossible to give a clear indication since the electrolyte is almost colorless and transparent.
Thus, it would be contemplated to use a float which is capable of always floating on the surface of the electrolyte and to give a vivid color to said float so that the float can be seen through the window instead of enabling the electrolyte surface to be seen directly.
On the other hand, in the case where the specific gravity of the electrolyte is to be indicated, generally, a float is used which floats or sinks, depending upon a change in the specific gravity of the electrolyte.
Arranging an indicating device using a float within a window formed in the lateral wall of the battery casing in order to indicate changes in the electrolyte conditions, however, raises technical problems in the manufacture of storage batteries.
That is, in the assembling process of storage batteries, there is included without fail the step of inserting an electrode plate assembly into the casing. In this case, since the electrode plate assembly is a relatively heavy object, it is more advantageous if a lesser number of operating steps are involved after the insertion of the electrode plate assembly into the casing. The reason is that the total weight of the casing and plate assembly makes moving the casing more difficult, whereby the manufacturing costs are increased. Therefore, it is desirable, if possible, that after the casing has been prepared, the indicating device as described above can be incorporated into the casing prior to the insertion of the electrode plate assembly.
In reality, however, it is impossible to incorporate an indicating device into the casing prior to the insertion of the electrode plate assembly, because the only space in the casing where such indicating device can be built-in, is above the electrode plate assembly. Further, particularly in order to indicate the amount of the electrolyte, an indicating device is not allowed to be positioned beside or below the electrode plate assembly since the electrolyte surface level must be above the top level of the electrode plate assembly. However, in the case where such indicating device is installed on the inner side of the lateral wall of the casing, such indicating device has a shape which projects more or less from the inner surface of the lateral casing wall. Thus, if the indicating device were incorporated into the casing prior to the installation of the plates, this would form a hindrance to the insertion of the electrode plate assembly into the casing. For this reason, the sequence of assembling process must be such that the indicating device is incorporated into the electrolytic vessel subsequently to the insertion of the electrode plate assembly. Hence, some compromise must be made with regard to the manufacturing cost.
In addition, although there is some space left above the electrode plate assembly in the casing for installing the indicating device, as described above, the size of that space is rather limited. Therefore, the indicating device itself must be reduced in size. However, if the indicating device is so reduced in size, it becomes inconvenient to handle and the operation of assembling some parts included in the indicating device by using the casing as a base during the assembling process of the storage battery, is not preferable as it lowers the efficiency of production of storage batteries.
Therefore, if the operation of assembling the indicating device into the casing must be preceded by the insertion of the electrode plate assembly, it is at least desired that the operation of assembling the indicating device be simplified.