The modern storage battery does not produce or generate electrical force. It was designed to carry an extra supply of current in storage to operate lighting and starting systems, and in most cases the current required for ignition is drawn from this supply.

A storage battery is also called an accumulator, as it accumulates and retains a charge of electrical current for future use.

Fig. 101 illustrates a storage battery with a section of the cell retainer case removed to show the location of the cells, their respective order, terminal posts and connections. A section of the cell jar, has also been removed to show the core, which consists of a set of positive and negative plates. The positive plates are inserted between the negative plates and are held in this position through their respective connections to the positive and negative terminal posts. The cell retainer-jars are made of zinc or rubber, and contain an acid and water solution called electrolyte into which the core is entirely immersed.

The Positive and Negative Plates.—The plates are held from direct contact with each other by a wood or rubber separator. These plates are formed with small sectional compartments called grids, into which a lead compound in paste form is pressed. The positive plates are made of lead oxide (zinc), and are dark gray in color, while the negative plates are made of pure lead, and are light gray in color.

Cells.—The cells are connected up in series, that is, the positive terminal post of one cell is connected to the negative terminal post of the next cell, forming a direct path through the cell arrangement. Each cell will retain a two-volt pressure until fully discharged. The voltage of a battery is determined by adding the number of two-volt cells that it contains.

Amperage.—The standard type of storage battery shown in Fig. 102 is composed of three two-volt cells which form a six-volt unit of sixty ampere hours, which means that a fully charged battery will deliver one ampere per hour for sixty hours. This, also, is about the rate of amperage consumed by the modern battery ignition system.

Electrolyte Solution.—The electrolyte solution is composed of a mixture of one part of sulphuric acid added to four to six parts of water. This solution is poured into the cell through the filler cap, until the plates are covered from one-fourth to one-half inch in depth as shown in Fig. 102.

Care should always be exercised to keep the air vent in the filler cap free from grease and dirt in order that the gases formed through evaporation may escape.

Battery Charging.—The cells are charged by passing a direct current through them, which causes a chemical action to take place as the current flows in, changing the nature of the positive and negative plates, thereby retaining a current force equal to the difference of the changed nature of the plates. The battery is entirely discharged when the plates become alike in nature.

Storage Battery Care and Maintenance.—Regularly once every week during the summer, and every two weeks during the winter, add water to each of the three cells of the battery, until the tops of the plates are covered. Use water only; never add acid of any kind. Water for battery purposes should be distilled fresh rain or melted ice, and must be free from alkali, iron, or other impurities. The battery should be kept clean and free from dirt. Use only clean non-metallic vessels for handling and storing water for battery purposes.

The state of charge of a battery is indicated by the specific gravity or density of the solution. Fig. 103 shows a hydrometer syringe used for taking specific gravity readings. The filler or vent plug in the top of the cell is removed and the rubber tube of the hydrometer syringe inserted into the cell so that the end of the tube is below the solution. Then squeeze the rubber bulb slowly, drawing the solution into the acid chamber until the hydrometer floats.

The reading on the graduator stem at the point where it emerges from the solution is the specific gravity or density of the solution.

Fig. 103 shows an enlarged section of the hydrometer floating so that the reading of the graduated scale is 1.280 at the point where it emerges from the solution. This is the specific gravity or density of the solution.

After testing, the solution must be returned to the cell from which it was taken.

Never take specific gravity readings immediately after adding water to the cells.

The specific gravity readings are expressed in “points,” thus the difference between 1.275 and 1.300 is 25 points.

When all the cells are in good condition the specific gravity will be approximately the same in all cells and the difference should not be greater than 25 to 30 points.

With a fully charged battery the specific gravity of the solution will be from 1.280 to 1.300.

Specific gravity readings above 1.200 indicates that the battery is more than half charged.

Specific gravity readings below 1.200, but above 1.150 indicates battery less than half charged.

Gravity below 1.150 indicates battery discharged or run down.

Should the gravity fall below 1.150 the gas motor should be given a long run with all lights turned off, to restore the battery.

This condition may result from leaving a car standing for prolonged periods with all lights in use and insufficient running of the gas motor in between these periods to replace the current taken to supply the lights.

When the specific gravity shows the battery to be half discharged, the lights should be used sparingly until the gravity rises to approximately 1.275.

If the specific gravity in one cell is much lower than that of the others, and if successive readings show the difference to be increasing, this indicates that the cell is not in good order.

If one cell regularly requires more water than the others (continually lowering the specific gravity), a leaky jar is indicated. Leaky jars should be replaced immediately.

If there is no leak and the specific gravity falls 50 to 75 points below that of the other cells in the battery, an internal short circuit is indicated and should be remedied.

Battery to Remain Idle.—Where a battery is to remain out of active service for a long period, it may be kept in good condition by giving it a freshening charge at least once a month, by running the gas motor idle.

When a battery has been out of service for some time it should be given a thorough charge before it is placed in service again.

If the gas motor cannot be run to give a freshening charge, the battery should be taken from the car and placed at a garage, which makes a business of charging storage batteries. It can be charged at least once a month. This charge should be 4 and ³⁄₄ to 5 amperes for twenty-four hours.

Battery Freezing.—In order to avoid freezing, a battery should be kept in a fully charged condition, as a fully charged battery will not freeze except at extreme temperatures. As a battery discharges the specific gravity of the solution decreases, and the specific gravity of a fully discharged battery will be approximately 1.120. Batteries of this low gravity will freeze at 20° F. above zero, whereas, the density of the solution in a battery approximately three-quarters charged will be 1.260, and a solution of this density will not freeze until 60° F. below zero.

See Accumulator. Chapter 14, Electrical Dictionary—Function and Chemical Action.