How Do I Test an AGM Deep Cycle Battery?

December 2, 2020 3:48 pm Published by Leave your thoughts

AGM batteries need to undergo regular testing in Houston, TX so you can ensure they will operate well into the future. But what is an AGM battery, and how do you know how to confirm a battery is an AGM?

Here’s an overview of what you should know.

Identifying an AGM battery

AGM stands for “absorbed glass mat,” a type of improved, advanced lead-based battery. These batteries are fully sealed and require very little to nothing in the way of maintenance. They also contain no fluid, unlike standard flooded-cell lead-acid batteries, which have sulfuric acid in their cells. This makes them safer for use, even if the casing gets cracked or otherwise damaged.

AGM batteries are most commonly used for motorized wheelchairs, golf carts and other similar types of equipment, and are also starting to be used more broadly in motor vehicles and boats.

Testing the battery

Here’s an overview of the processes you need to go through for a standard test of an AGM battery using a multimeter:

  • Get your multimeter: Turn on the multimeter, and set it to measure voltage by turning the dial or pressing the proper button on the meter.
  • Connect: Put the sensor on the end of the red wire coming off the multimeter onto the positive terminal of the AGM battery. The black wire’s sensor should go on the negative terminal of the battery.
  • Measure and record: A fully charged standard AGM battery should have an output voltage of approximately 13 volts, just higher than the 12 volts likely to be labeled on the side of the battery. If the reading comes in below 10 volts, you need to let your battery recharge. After it’s charged, test the voltage and then retest several hours later. If the voltage reading drops more than a volt or two in the retest, you probably need a new battery.

You can also perform an AGM load test, which works as follows:

  • Find the ampere rating: On the battery’s label, you’ll find the ampere rating, which is indicated with CCA (cold cranking amps). It might also have the letters “Ah” (for ampere hours) followed by a number, if it’s on a golf cart.
  • Calculate: Divide the ampere rating by two. The resulting figure is what you should get from the load test meter, if the battery is charged and operational.
  • Attach the load tester: Attach the load tester’s clips to the battery terminal, with the red clip going to the positive terminal and the black clip going to the negative terminal.
  • Begin the test: Let the load test run for 10 to 15 seconds, then stop.
  • Read the results: The resulting figure should be the same as your calculated ampere figure. However, if it’s below that figure by more than 10 percent, you’ll need to charge the battery. As with the above method, test again after charging, then retest several hours later. If the figure remains more than 10 percent below, you’ll need to get a replacement.

If you wish to perform a deep cycle battery test beyond the standard testing procedures described above, know that you’ll need to perform more thorough testing procedures than those that can be done in a short 15- to 30-second test.

For example, if you’re using a 35 amp hour 12 volt battery, you should check to make sure the battery is fully charged with an automatic industrial charger designed for AGM batteries. If the charger indicates a full charge, you can remove the battery. Check the factory ratings to determine the specific discharge test you’ll use. There should be specifications with a scale stating the amperage rate you need for a certain time at a certain voltage.

The average we look for is 25 amps to an ending voltage of 9 volts in an hour or more, at a temperature of around 77 degrees.

For more information about how to test an AGM deep cycle battery in Houston, TX, contact Texford Battery Co. today.

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