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AGM (Absorbed Glass Mat) batteries are renowned for their ability to outlast regular lead acid batteries. AGMs are completely spill and leak proof thanks to their construction. These car batteries are new to the automotive world – a design that replaces conventional acid flooding of the battery cells with absorbent separators and cells held under compression.



What is an AGM Battery?

AGM is an advanced battery technology that allows the electrolyte (acid) to be uniformly distributed across the battery plate active material. This allows the battery to tolerate repeated deep discharges and provides an overall longer service life. AGM batteries are safer because there is no free acid to spill and they are highly resistant to failure from vibration. They also allow installation in virtually any location (even at odd angles) and are famous for lasting up to two times longer than regular lead acid batteries.

How do AGM Batteries Work?

These batteries are constructed with glass mat separators designed to wick the battery electrolyte between the series of battery plates. The electrolyte is held in the glass mats, as opposed to freely flooding the plates like in a lead-acid battery. Very thin glass fibers are woven into a mat to increase surface area enough to hold sufficient electrolyte on the cells for their lifetime. The electrolyte is distributed evenly across the active plate material. and contains only enough liquid to keep the absorbed mat wet with the electrolyte. The maximization of electrolyte-to-plate coverage enables these batteries to far exceed the performance of conventional flooded lead acid batteries. AGM batteries are known as safe non-spilling car batteries.

How are AGM Batteries Made?

Plates and separators are compressed prior to insertion into the case, allowing them to be held tightly - a technique that lends to vibration resistance. The glass mat plates allow for the even distribution of electrolyte over the entire surface area of its adjacent lead plate, due to its ability to hold acid. The plates in an AGM battery may be any shape: flat, bent, or rolled. AGM batteries, both deep cycle and starting, can be built in a conventional rectangular case or other design.

Why do AGM Batteries Fail?

  • As with all batteries, the active material eventually wears out
  • Gradual capacity decline over time means more predictable replacement intervals
  • Overcharging. AGM is more sensitive to being overcharged, which will shorten life
  • Keeping battery in an extended discharged state
  • Must be stored in charged condition

What are the Symptoms of AGM Battery Failure?

  • A change in the sound of the starter (decrease in cranking speed) is the best indicator of impending failure
  • A 12-volt battery should be between 13.2 -13.8 volts at rest. When the battery can’t hold a charge, it is getting close to dying

What are Consequences of AGM Battery Failure?

  • Complete failure most frequently results in a no-start condition
  • The alternator is designed to replenish the battery. A battery that is failing can damage an alternator if not replaced when required

If you have questions or concerns about AGM batteries or any of your vehicle’s components, come into your local Pep Boys where we can answer any question, help you find any part, or perform any vehicle service you might need.

If you want to learn more about other car parts, especially as they apply to your vehicle’s electrical system, we recommend reading up on alternators, starters and lead acid batteries.