STORAGE BATTERY, a battery which when charged can be used for some time as a source of electric cur rent. Gautberot, in 1801, first conceived the idea of such a battery. Faraday, in his "Researches," mentions its prac ticality. However, it was left to Gaston Plante, in 1860, to construct a practical storage battery.
Storage batteries are of two types— those using lead plates in an acid medium and those using iron-nickel plates in an alkaline medium. The former are subdivided into the Plante cells and the Faure, or "pasted" cells. The reaction which occurs in both the Plante and Faure cells is indicated by the following equation: Pb02 2112SO4 Pb Lead Oxide Sulphuric Lead Acid PbSO4 + 211,0 PbSO4 Lead Water Lead Sulphate Sulphate When the battery is being charged the reaction takes place from right to left; that is to say, the lead sulphate on the plates is decomposed, producing lead peroxide on one plate and spongy lead on the other, while sulphuric acid is added to the electrolyte, its specific gravity being thereby increased. When the battery is being discharged, the re action is reversed and takes place from left to right. In other words, sulphuric acid is taken from the electrolyte to form lead sulphate on both plates, so that the specific gravity falls. In the Plante cell, the active material on the plates is formed by passage of an elec tric current through the cell. In order to speed up this process, the lead plates are covered with grooves, so as to pre sent as much surface to the acid as pos sible. At best, however, this is a slow process, and in order to bring about the same result in less time, the Faure or "pasted" cells were invented. In these, a paste of lead oxide is spread on to a supporting grid of lead. On charging, the material on the positive plate is con verted to lead peroxide, while on the negative plate it is reduced to spongy lead.
The Edison battery uses plates of iron and nickel in a bath of caustic potash. The plates consist of shallow perforated tubes of nickel-plated steel, fixed in a sheet-steel grid. In the positive plate, the tubes are filled with alternate layers of nickel hydroxide and flaked metallic nickel. The negative plate contains
powdered iron oxide. The reactions which take place are represented by: 2Ni0. + Fe = Ni3O3± FeO. During dis charge, the reaction proceeds from left to right; that is, oxygen is transferred from the nickel oxide to the iron. On charging, the action is reversed, the higher nickel oxide being produced, while the iron oxide is reduced to iron. In other words, charge and discharge re sult in a transfer of oxygen from one plate to another, so that no change in the specific gravity of the electrolyte occurs. The chief advantages of the battery are its lightness and the fact that it can remain charged or discharged for any length of time without injury. Its disadvantages are its high cost and its comparatively low efficiency.
The best advice to give as to the treat ment of a storage battery is to follow the manufacturers' instructions. Al though all makes of storage battery are built on the principles outlined above, each one has its own special features, and no one is so familiar with its pecu liar requirements as the manufacturers. The following instructions apply, how ever, to all makes.
Cells should never be over discharged, because, in the lead cell, when the termi nal voltage drops below 1.8 there is a tendency for the plates to buckle and for an insoluble sulphate to be produced. This process is known as "sulphation." For similar reasons, the cell should not be allowed to stand discharged for any length of time. If a battery is not in use for several weeks, it should be charged at least once a month, and, bet ter, once every two weeks. As the electrolyte evaporates, the cell should be re-filled with pure, distilled water. The electrolyte should never be per /pitted to sink below the level of the top of the plate. The acid does not evaporate and should not need renewing. But if some is accidentally spilled, it should be replaced with chemically pure sulphuric acid of the specific gravity recom mended by the makers of the cell. In the case of the Edison cell, a 21 per cent. solution of caustic potash is used instead of sulphuric acid.