How to Know If Your Battery Cables Are Bad

by Jerry Walch Google

    Checking the condition of your battery cables is a two-step process. The first step is to disconnect the cables from the battery posts; cleaning the cable terminals and battery posts; and then performing a visual inspection of the cables. The second step is to reconnect the battery cables and perform a voltage drop test on the cables using a digital multimeter. This is a project that even the neophyte DIY auto mechanic can accomplish without difficulty.

    Items you will need

    • Safety goggles or face-shield
    • Rubber gloves
    • Battery terminal wrench
    • Battery terminal puller
    • Plastic container
    • Baking soda
    • Paint brush
    • Battery terminal brush
    • Rags
    • Anti-corrosion spray or grease
    • Felt washers
    • Digital, auto-ranging multimeter

    Performing the Visual Inspection

    Step 1

    Park the car on a level surface and set the emergency brake. Move the shifting selector to park and raise the hood.

    Step 2

    Put on rubber gloves and safety goggles,then loosen the nut securing the negative battery cable with a terminal wrench. The negative battery post can be identified in two ways: by the “-” sign embossed next to it on the battery, and by its smaller diameter compared to the positive post.

    Step 3

    Remove the negative battery cable terminal from the battery post first, using the terminal puller. Remove the positive terminal second, in like manner.

    Step 4

    Mix a baking soda and water paste in a plastic container, then brush a thick coat onto the battery posts and cable terminals. Allow the paste to set for 15 minutes and then it rinse off with plenty of water. Wipe the battery posts and cable terminal dry with rags. Clean the posts and terminals with a battery terminal brush.

    Step 5

    Inspect the terminals at the ends of both cables for broken copper wire strands. Inspect the battery posts for cracks. Replace any damaged cables if they appear damaged. Replace the battery if the posts have cracks. Spray the battery posts with anti-corrosion spray and place red and green felt washers on the positive and negative battery posts, respectively. Do not pound on the terminals to get them to seat fully. If necessary, spread the terminal ends with a large flat-head screwdriver or equivalent. Tighten the battery terminal bolts securely.

    Perfoming the Voltage Drop Tests

    Step 1

    Set the range selector switch on your auto-ranging meter to the direct current voltage function. The polarity of the test probes will not matter when making these tests.

    Step 2

    Start the car's engine and place one of the meter's test probes in the center of the “-” battery post and the other test probe on the negative battery cable terminal. Make sure that the second probe is not touching the battery post. Your meter should display “0.00” on its LCD if the cable is good.

    Step 3

    Check the positive cable end in a like manner.

    Step 4

    Check the voltage drop across the positive battery cable by placing one of the meter probes on the “Positive” battery terminal and the other probe on the other end of the cable. The meter should display a voltage drop of “0.20” volts or less. Any reading higher than 0.20 volts indicates high resistance in the cable, meaning that the cable is defective.

    Step 5

    Test the "Negative” battery cable in like manner.

    Warning

    • Always disconnect the negative cable first to prevent an accidental short that could cause the battery to explode. Connect the negative cable last when reconnecting the battery.

    Photo Credits

    • Polka Dot Images/Polka Dot/Getty Images