AUTOMOTIVE BATTERIES

2. WHY BOTHER?

Because only the rich can afford cheap batteries... A car battery is a rechargeable electrochemical 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, chemical energy is converted to electrical energy and current flows through the circuit. A good quality car battery will cost between $50 and $150 and, if properly maintained, it should last an average of five years. The primary purpose of a car (or SLI-Starting, Lighting and Ignition as it is known in the battery industry) battery is to START the engine. Its secondary function is to filter or stabilize the power. It also provides extra power for the lighting, two-way radios, audio system and other accessories when their combined load EXCEEDS the capability of the charging system. Finally, a car battery provides a source of power to the electrical system when the charging system is not operating. With a 5% compounded annual growth rate, worldwide sales of SLI batteries represent 63% of the $27 billion annually spent on batteries.

2.1. How is a battery made?

There is an excellent description of how battery is made at the Battery Council International (BCI) web site at http://www.batterycouncil.org/made.html. A twelve-volt car 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. In Europe, using solid lead positive "Plante" plates is popular.
[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 recharged when they are put into service.
[Source: BCI]

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 temperature, the better the diffusion.

2.2. How does a battery work?

[Source: BCI]

A more detailed description of how a battery works can be found on the BCI web site at http://www.batterycouncil.org/works.html. 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 lead-acid battery produces approximately 2.1 volts per cell. The chemical action between the metals and the electrolyte 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. The 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 determine the action of the lead-acid storage battery.

2.3. Why do batteries die?

In cold climates, normally a battery "ages" as the active positive plate material sheds (or flakes off) due to the expansion and contraction that occurs during the discharge and recharge cycles. Brown sediment, called sludge or "mud," builds up in the bottom of the case andcan short the cell out. In hot climates, additional 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, over charging, under charging or non-use accelerate this "aging" process. Another major cause of premature battery failure is lead sulfation. Please see Section 16 for more information on sulfation. Using tap water to refill batteries can produce calcium sulfate that also will coat the plates and fill the pores. Recharging a sulfated battery is like trying to wash your hands with gloves on. When the active material in the plates can no longer sustain a discharge current, the battery "dies." In a hot climate, the harshest environment for a battery, a Johnson Controls Inc. survey of junk batteries revealed that the AVERAGE life of a good quality 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 and load tested. Dead batteries almost always occur at the most inopportune times, for example, AFTER you have jump-started your car, in the airport after returning home from a long trip, during bad weather, late at night in a dark parking lot, 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, a tow, or a taxi. Most of the "defective" batteries returned to manufacturers during free placement warranty periods are good. This suggests that most sellers of new batteries do not know how to or take the time to properly load test or recharge them.

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