Tech Tip: Testing AGM Batteries

Tech Tip: Testing AGM Batteries

AGM (Absorbed Glass Mat) batteries are in the most sophisticated and power hungry vehicles. These batteries are more deep cycle in nature and considered to be more durable within certain parameters. AGM recombinant batteries have a very low internal resistance reducing heat during high charge/discharge levels and very low static charge loss of about 1% to 3% per month.

By Rob Morrell
WORLDPAC Training Institute (WTI) Director of Technical Training

AGM (Absorbed Glass Mat) batteries are in the most sophisticated and power hungry vehicles. These batteries are more deep cycle in nature and considered to be more durable within certain parameters. AGM recombinant batteries have a very low internal resistance reducing heat during high charge/discharge levels and very low static charge loss of about 1% to 3% per month.

AGM batteries are used in vehicles with high potential load, therefore an AGM battery should only be replaced with another AGM Battery of equal capacity. A common mistake is replacing an AGM with a regular wet lead acid battery and may destroy the regular wet battery within a couple weeks because of the high demands on it.

Charging of the AGM battery also needs special attention; the charging voltage cannot exceed 14.8 volts even for short periods of time without damaging an AGM battery. AGM Batteries can withstand very high charging currents, but not voltage; a slow charge is always the best, most efficient practice. High heat from an engine compartment can also dramatically reduce the AGM battery life; these batteries were never designed for higher temperatures.

To test a high capacity AGM battery, you must begin with a fully charged battery (see ‘Battery Conditions’ below). You can usually remove the surface charge by turning the key on for about three minutes. Conductance battery testers can usually work well if they have the right information, but appear to be more accurate with wet type batteries than AGM models; AGM batteries sometimes give false positive results. A load test is the best testing method to avoid unnecessary comebacks.

AGM batteries should be load tested for 15 seconds at:
• 1/2 the CCA rating (Cold Cranking Amps); and
• 3 times the Ah rating (Amp hour rating).
NOTE: The voltage must not drop below 9.7 volts for the duration of the test.

Battery Conditions
12.65 V = 100% charge
12.45 V = 75% charge
12.24 V = 50% charge
12.06 V = 25% charge
11.89 V = 0% charge

Tech Tip courtesy of WORLDPAC Training Institute (WTI).

For additional information on WORLDPAC Training Institute (WTI) and products offered by WORLDPAC, visit www.worldpac.com.

You May Also Like

Were things better when they were simpler? Probably not.  

Last month, Andrew Markel purchased a 1982 Chrysler New Yorker for $1,500.

1982 Chrysler New Yorker

Last month, I purchased a 1982 Chrysler New Yorker for $1,500. The car was previously owned by a technician who was moving to Arizona. It had 67,000 original miles. It would be my “beater with a heater” for this winter.

Under the hood is a 318 V8 with a Lean Burn feedback carburetor with a rudimentary engine control module attached to the air cleaner. The system could adjust the spark advance, change metering in the carburetor and even open a solenoid to vent the evaporative emissions from the fuel tank.

Branford Public Schools Award $60M Transportation Contract to Zum

Within five years, Zum will transition Branford to a 100% electric school bus fleet, the first in Connecticut.

Tesla Model 3 TPMS Service

Resetting and programming TPMS sensors for a Tesla is a lot like any other vehicle, and the challenge is still the same: keeping the light off.

Can You Jumpstart an EV?

First thing’s first: Find the LV battery, which could be anywhere in the vehicle.

ADAS Module Programming

Reflashing and reprogramming is a necessary service for repairing vehicles.

Other Posts

Mullen Road Tests Solid-State Polymer Battery Pack

The results met or exceeded all requirements targeted for the first drive cycles for energy usage and driving range.

Understanding What Antifreeze/Coolant Actually Does

Today, each manufacturer has its own formula for best results in their vehicles. This video is part of the Group Training Academy.

How The Vehicle Cooling System Functions

Here’s what to know to clarify cooling questions you’re asked at the service counter. This video is part of The Group Training Academy.

Oil Filter Housing Weak Points & Standard® Solutions

Engineers at Standard® have created a completely assembled Oil Filter Housing Kit.