Test Car Batteries
Batteries commonly used in present-day vehicles are of the lead acid type. These batteries typically use two types of plates--a lead plate and a lead dioxide plate separated by a non-conductive material to keep the plates from touching one another. A solution of water and 33.5 percent sulfuric acid creates the reaction. The voltage range on the typical six-cell battery in an open or quiescent state at full charge is 12.6 to 12.8 volts. The maximum voltage to quick charge a drained battery is 15 volts for no more than two hours with constant monitoring on the heat range.
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Instructions
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1
Check the terminals for corrosion and security. If they are corroded, clean them with a baking soda and water mixture. If the battery cables are loose, tighten them with the proper size socket. If the terminal itself is loose, discard the battery.
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2
Lift the caps off the top of the battery, exposing the cells. Check the water level in the cells and add distilled water as necessary so all of the cells are at the same level.
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3
Insert the hydrometer in the first cell, and squeeze the tube to fill the hydrometer. Record the reading and do the same for the remainder of the cells. A fully charged battery will register 1250 specific gravity of the electrolyte. If all of the cells are the same, but lower, the battery needs to be charged. If one cell is more than 20 percent different than the rest, it is either starting to wear out or could possibly be shorted.
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4
Reinstall the caps covering the cells. Charge the battery if the reading on the hydrometer was low before moving on to the next step. A battery can't be diagnosed properly if it is discharged.
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5
Using the voltmeter, check the battery for voltage. Install the red wire from the voltmeter on the battery's positive terminal and the black on the negative. Turn the voltmeter on and adjust to 20 volts. Take the reading, which should be 12.6 to 12.8 volts. If the battery was slow charged for more than three hours and still shows less than the proper voltage, discard the battery.
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6
Install the battery load tester on the terminals. Find the amount of cold cranking amps for which the battery was designed on the battery label. This will be designated as CCA followed by the number of amps. For example, CCA 550 means 550 cold cranking amps are available to start the car in freezing weather. The load tester will show the different CCA amps and what the reading should be for that particular battery when the load is applied. The load tester puts a drain on the battery as if you were to turn on all of the car's accessories. Push the load tester switch for 10 seconds and watch the voltage to see if it stays within limits. If not, the battery has a shorted cell and should be replaced.
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Tips & Warnings
Use a slow charge should to fully charge a discharged battery. The slow charge should be no more than 13.5 volts at 5 amps.
Batteries tend to heat up as they are charged and give off hydrogen, which is explosive. Open flame should be kept away from a battery being charged. Battery acid will give you an acid burn if it gets on your skin or in your eyes.
