How to Check an Auto Battery for Load

A load tester connects to the battery using two clamp-type cables.

An automotive battery is the backbone of the automotive electrical system. A properly functioning battery must be installed in the automobile for an automobile's electrical system to work properly. One way to determine if a battery is functioning properly is to conduct a load test. A load tester draws a large electrical current from the battery for a short period. If the battery voltage after the load test is at or above a certain level, the battery is considered to be functioning properly.

Things You'll Need

• Automotive battery (12 volt)
• Battery load tester
• Digital or analog multimeter

Instructions

1. Place the positive (red) multimeter probe on the positive battery terminal. Place the negative (black) multimeter probe on the negative battery terminal. Turn the measurement scale to "Volts DC."

2. Check the multimeter display. If the multimeter reading displays more than 12.4 volts, remove the multimeter probes and turn off the multimeter.

3. Attach the red lead from the battery load tester to the positive battery terminal. Attach the black lead from the battery load tester to the negative battery terminal.

4. Load the battery by turning the load increase control until the ammeter on the load tester reads three times the amp-hour rating or one half the cold-cranking ampere rating. The battery cold-cranking ampere rating or the amp-hour rating appears on a sticker at the top of the battery.

5. Run the test for 15 seconds, and then turn off the load tester.

6. Place the positive (red) multimeter probe on the positive battery terminal. Place the negative (black) multimeter probe on the negative battery terminal. Turn on the multimeter, and verify the voltage. A battery in proper working order will show a reading of at least 9.6 volts.

Tips & Warnings

• Always remember to recharge the battery to at least 12.6 volts after a load test.

• If the multimeter reading displays less than 12.4 volts, turn off the multimeter and remove the multimeter leads from the battery. Do not attempt to load test the battery, as it may become unusable if it is load tested under this condition.

• If the battery voltage is less than 9.6 volts after load testing, replace the battery as soon as possible.

References

• Autoshop 101: Battery Service
• "Battery Maintenance"; Mike Allen; 2000