Truck News


The ABCs of AGM

One truck battery can look like the next. The charged cubes all include positive and negative terminals and they are all called upon to offer the energy for everything from starting requirements to ba...

One truck battery can look like the next. The charged cubes all include positive and negative terminals and they are all called upon to offer the energy for everything from starting requirements to battery-powered HVAC systems.

That is where the similarities end.

Thanks to the absorbent material between the plates of an Absorbed Glass Mat (AGM) battery, these sealed designs resist damage from vibration, will not spill and can offer 1.5 times as many cycles as a dual-purpose flooded battery.

They may cost twice as much as their flooded counterparts -and can be 6 lbs heavier -but some test results unveiled during a recent meeting of the Technology and Maintenance Council suggest that the investment may be worthwhile. One fleet compared 68 trucks with flooded batteries to 69 trucks with AGM batteries. Just 34 months later, maintenance teams had replaced 113 of the flooded batteries and a mere eight of the AGM designs.

The advantages don’t end there. A lower internal resistance means the batteries can be recharged in half the time. And an AGM offers a higher capacity and improved power density, says Jeff Coleman, director of OEM sales for East Penn/Deka.

It explains the growing popularity of the AGM batteries in trucks that need additional cranking power or extra cycle life.

Fleet maintenance managers simply need to be aware of the related maintenance issues that emerge.

To start with, AGM batteries should not be mixed with flooded batteries in the same battery pack for an extended period of time.

The batteries will also require different charging and testing procedures, notes Fred Feres a senior engineering manager at Exide Battery. If the AGM is not damaged, and the Open Circuit Voltage (OCV) is higher than 12.6 volts, the shop can begin load testing. If the voltage is lower than that, the battery has to be charged.

When trying to determine the battery’s state of charge while everything is still on the vehicle, mechanics will need to stop the engine, turn on the high beams, set the fan blower on high for one minute, and then switch off the high beams and blower to allow the battery to rest in an open circuit for five minutes. Then the voltage can be tested.

If the batteries are removed from the vehicle, mechanics will need to apply a load at 300 amps or half the battery’s CCA rating for 15 seconds, and then wait up to 10 minutes before testing the voltage at the battery terminals.

“You can’t use just any charger,” Feres adds, referring to those that are designed for AGM models. The DC voltage needs to be regulated to between 14.1 and 14.6 volts, and the chargers need to automatically terminate once the process is complete.

Charging can be performed on the vehicle, but the better option is to remove the batteries in the shop, he adds.

The charging process should also take place between 15 and 30 Celsius. The best approach is to charge the batteries in parallel, while the output should be rated to provide 10 to 35 amps of maximum charging power per battery. Terminal adaptors should also be used to prevent damage to the threads.

In most cases, charger labels will indicate whether or not an individual piece of equipment can be used on an AGM battery. To ensure everything is okay, connect the charger to a fully charged AGM battery at 12.8 volts or more at room temperature. After three hours of consecutive charging, the maximum voltage should be between 13.8 and 14.6 volts.

There is a learning curve, to be sure, but the industry has adapted to battery changes in the past.

Decades ago, the batteries still had filler caps. Now the hydrometers have been relegated to the bottom of old toolboxes.

Who knows how long flooded batteries will remain.

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