How to Test an AGM Battery

by Stephen Benham

Absorbed Glass Mat (AGM) batteries are the latest improvement to lead-based batteries. AGM batteries are completely sealed units and are maintenance-free. Unlike a regular flooded-cell lead-acid battery that contains sulfuric acid in the cells, an AGM battery doesn't contain any fluid. This means they are safer, as even if the outer casing gets damaged or cracked, no leakage will occur. AGM batteries are a popular choice for use in golf carts and motorized wheelchairs and are increasingly fitted in marine vessels and motor vehicles.

AGM Multimeter Test

Turn on the multimeter. Set it to measure voltage by turning the dial or pressing the appropriate button on the meter.

Place the sensor on the end of the red wire from the meter onto the "+" terminal of the AGM battery. Place the sensor on the end of the black wire onto the "-" terminal of the AGM battery.

Read the multimeter display. A fully charged AGM battery has an output voltage of about 13 volts. This is slightly higher than the 12 volts you find labeled on the side of the battery to allow for voltage resistance in the battery cables. However, if the reading is below 10 volts, you need to recharge your battery for a while. Once charged, test the voltage again, then leave it for several hours and retest it. If the voltage reading drops more than about 1 or 2 volts, you may need to consider getting a replacement.

AGM Load Test

Read the label on the side of the AGM battery to find out the ampere rating. The label has the letters CCA, meaning cold cranking amps, followed by a number that relates to the amperes, if the battery is for use in a vehicle. For example, it may have CCA 70 written on the label. Alternatively, it may have the letters Ah, meaning ampere hours, followed by a number, if the battery is used in a golf cart.

Divide the CCA or Ah by 2 using a calculator. For example, if the label reads CCA 70, divide 70 by 2 to get 35. This is the figure you will get from the load-test meter, if your battery is charged and in good condition.

Turn on your load tester. Attach the alligator clips to the battery terminals; the clip on the end of the red wire goes to the "+" terminal and the clip on the end of the black wire goes to the "-" terminal.

Press the load-test start button. Let the test run for 10 to 15 seconds and then stop the test. Most load testers automatically stop after 15 seconds.

Read the load test meter. Expect it to read the same as the ampere figure you calculated earlier. If the reading is more than 10 percent below the figure you calculated, charge your battery until full. Leave it to stand for a few hours and test again. If the figure is still more than 10 percent below the figure you calculated, you need to consider getting a replacement.

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About the Author

Stephen Benham has been writing since 1999. His current articles appear on various websites. Benham has worked as an insurance research writer for Axco Services, producing reports in many countries. He has been an underwriting member at Lloyd's of London and a director of three companies. Benham has a diploma in business studies from South Essex College, U.K.

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