2.  WHY BOTHER?

Because only the rich can afford cheap batteries.....

A car battery is a rechargeable electro chemical device that stores chemical energy and releases it as electrical energy upon demand.  When a car battery is connected to an external device, such as a starter motor, chemical energy is converted to electrical energy and direct current flows through the circuit.  A good quality lead-acid car battery will cost between $50 and $150 and, if properly maintained, it should last five years or more.  The four major purposes of a car, starting, cranking, or SLI (Starting, Lighting and Ignition) battery, as it is known in the battery industry, are:

o To start the engine.

o To filter or stabilize the power.

o To provide extra power for the lighting, two-way radios, audio system and other accessories when their combined load exceeds the capability of the charging system.

o To supply a source of power to the vehicle's electrical system when the charging system is not operating.

With a 5% compounded annual growth rate, worldwide sales of SLI batteries represent roughly 63% of the estimated $30 billion annually spent on lead-acid batteries.

2.1. How is a battery made?

A 12-volt lead-acid battery is made up of six cells, each producing 2.1 volts and that are connected in series from positive to negative.  Each cell is made up of an element containing positive plates that are all connected together and negative plates, which are also all connected together.  They are individually separated with thin sheets of electrically insulating, porous material "envelopes" [labeled #3 in the diagram below] that are used as spacers between the positive (usually light orange) and negative (usually slate gray) plates to keep them from electrically shorting to each other.  The plates [#2 in the diagram below], within a cell, alternate with a positive plate, a negative plate and so on.  A plate is made up of a metal grid that serves as the supporting framework for the active porous material that is "pasted" on it.

            

[Source: BCI]

After the "curing" of the plates, they are made up into cells, and the cells are inserted into a high-density tough polypropylene or hard rubber case [#1 in the diagram above].  The cells are connected to the terminals [#5 in the diagram above], and the case is covered and then filled with a dilute sulfuric acid electrolyte [#4 in the diagram above].  The battery is initially charged or "formed" to convert yellow Lead Oxide (PbO or Litharge) into Lead Peroxide (PbO₂), which is usually dark brown or black.  The electrolyte is replaced and the battery is given a finishing charge.  Some batteries are "dry charged" meaning that the batteries are shipped without electrolyte and it is added and charged when they are put into service.

[Source: BCI]

[Source: Varta]

Two important considerations in battery construction are porosity and diffusion.  Porosity is the pits and tunnels in the plate that allows the sulphuric acid to get to the interior of the plate.  Diffusion is the spreading, intermingling and mixing of one fluid with another.  When you are using your battery, the fresh acid needs to be in contact with the plate material and the water generated needs to be carried away from the plate.  The larger the pores or warmer the electrolyte, the better the diffusion.

There is an excellent detailed description of how battery is made on the BCI (Battery Council International) web site at www.battery.council.org

2.2. How does a battery work?

[Source: BCI]

A battery is created by alternating two different metals such as Lead Dioxide (PbO₂), the positive plates, and Sponger lead (Pb), the negative plates.  Then the plates are immersed in diluted Sulfuric Acid (H₂SO₄), the electrolyte.  The types of metals and the electrolyte used will determine the output of a cell.  A typical fully charged lead-acid battery produces approximately 2.11 volts per cell.  The chemical action between the metals and the electrolyte (battery acid) creates the electrical energy.  Energy flows from the battery as soon as there is an electrical load, for example, a starter motor, that completes a circuit between the positive and negative terminals.  Electrical current flows as charged portions of acid (ions) between the battery plates and as electrons through the external circuit.  The action of the lead-acid storage battery is determined by chemicals used, State-of-Charge, temperature, porosity, diffusion, and load.

A more detailed description of how a battery works can be found on the BCI web site at www.batterycouncil.org

2.3.  Why do batteries die?

When the active material in the plates can no longer sustain a discharge current, the battery "dies". Normally a battery "ages" as the active positive plate material sheds (or flakes off) due to the normal expansion and contraction that occurs during the discharge and charge cycles. This causes a loss of plate capacity and a brown sediment, called sludge or "mud," that builds up in the bottom of the case and can short the plates of a cell out.  In hot climates, additional major causes of failure are positive grid growth, positive grid metal corrosion in the electrolyte, negative grid shrinkage, buckling of plates, or loss of water.  Deep discharges, heat, vibration, and over charging accelerate the "aging" process.

Another major cause of premature battery failure is sulfation. It is caused when a battery's State-of-Charge drops below 100% for long periods or under charging. Hard lead sulfate fills the pours and coats the plates. Please see Section 16 for more information on sulfation.  Recharging a sulfated battery is like trying to wash your hands with gloves on.  Using tap water to refill batteries can produce calcium sulfate that can also fill the pores and coat the plates.

In a hot climate, the harshest environment for a battery, a Johnson Controls survey of junk batteries revealed that the average life of a car battery was 37 months.  If your car battery is more than three years old, then it is living on borrowed time.  Abnormally slow cranking, especially on a cold day, is another good indication that your battery is going bad. It should be externally recharged, surface charge removed, and load tested.  Dead batteries almost always occur at the most inopportune times, for example, after you have jump-started your car, late at night in a dark airport parking lot after returning from a long trip, during bad weather, or when you are late for an appointment. You can easily spend the cost of a new battery or more for an emergency jump start or a tow or for a taxi ride.

According to the manufacturers and distributors, most of the "defective" batteries returned during free replacement warranty periods are good.  This suggests that some dealers of new batteries do not know how or take the time to properly recharge or test them. This situation is improving with the widespread use of easy to use conductance type battery testers made by Midtronics, for example.

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