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CAUTION: BATTERIES CONTAIN SULFURIC ACID. ALWAYS WEAR EYE PROTECTION WHEN WORKING ON A BATTERY. BATTERIES PRODUCE HYDROGEN GAS, DO NOT SMOKE OR CAUSE SPARKS THAT MAY IGNITE THE GAS AND CAUSE AN EXPLOSION.
  There are three main parts to the charging system, the Alternator, the Voltage Regulator and the battery.
   Car batteries are of a lead-acid type. Most of the world production of lead goes into car batteries and an estimated 95% of all car batteries are recycled so the lead can be used again and again. The positive plates in a battery are made from lead dioxide and the negative plates are made from metallic lead. The electrolyte inside the battery is a sulfuric acid solution. As the cell discharges, the acid electrolyte is consumed producing water and both electrodes change into lead sulfate. When the cell is recharged, the process reverses. A 12-volt battery has six cells connected in series making a total of 12 volts.
    There are several ways to test a battery to see how good it is. The quickest and easiest is the load test. A predetermined load is placed across the battery terminals and held for ten seconds. At the end of the ten seconds the voltage across the terminals is measured and this voltage determines how good the battery is. If the voltage stays above 11 volts, the battery is good and healthy. If the voltage drops between 9 and 11 volts, the battery is determined to be borderline. It will be okay in warm weather, but may fail as the temperature drops toward freezing. If the voltage drops below 9 volts, it's no good.
    The way we test the batteries state of charge is with a battery hydrometer. A hydrometer measures the specific gravity of the acid solution. The higher the specific gravity, the more charge in the battery.
   A fully charged battery will have a specific gravity of 12.75. A weak battery will have a specific gravity of 12.50 or 12.25. A discharged battery will have a specific gravity of 12.00 or less. When you check the battery, you need to check each cell. All six cells must have the same specific gravity. If five cells test at 12.75 and one tests at 12.25, you have may have a bad cell.
   Charge the battery for about 30 minutes and test again. If the low cell does not come up, it's bad and you need a new battery. Some variance is allowed between cells but if it is a large variance, you may have battery problems.    Take a coat hanger and make two lead extensions about six inches long and attach them to the meters test leads. Touch the positive lead to the positive terminal and stick the negative lead inside the cell next to it. It should read about 2.1 to 2.3 volts. Now insert the positive lead in the first cell and the negative lead in the second cell. Proceed down the line until you get to the last cell. Here you will put the positive lead in the last cell and the negative lead on the negative terminal. All the cells should read the same, or within 0.2 volts. If one reads 4.0 or more, you have a shorted cell and the battery is no good. If you get a very low reading or a zero reading, the cell is open and again the battery is no good.

  Whenever you disconnect a battery, ALWAYS disconnect the negative cable first. This will prevent sparks that may cause the gasses inside the battery from igniting. Wear safety glasses, batteries contain sulfuric acid and it can splash if you are not careful. If it comes in contact with your skin, wash it off with plenty of water. Take off any rings or jewelry when you work on a battery.
 
 
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