An alternative test is to just let the battery sit and take daily voltage measurements. But this takes time. Anything less than a week or two is not really useful.
AGM batteries are tough customers to test. They are accomplished "liars". A 90% charged AGM will load test so close to a 100% charged AGM that not even a "polygraph" can sort out the Pinocchio. CCA. Load testing, because it truly is intelligent and simple has almost disappeared.
A 500-amp adjustable load tester can be used to load a 180 ampere hour telecomm battery for a full 30-seconds at say, 250 amperes. Watch the voltage carefully. It should drop to an "X" amount of volts then remain there - within .2 - .3 tenths of a volt span. It should NOT continue to drop "quickly".
Stop the load draw.
Watch the voltage recovery
Each type of battery will recover differently. AGM batteries recover voltage much more quickly than say flooded antimony batteries.
Here is a symptom.
After a load test, voltage rises slowly from it's minimum during the load test. This is not a good sign. This is a sick AGM battery.
The trick is to find someone with an adjustable carbon pile load tester.
Lifeline has in PDF Manual format an excellent description of an AGM BATTERY CAPACITY TEST. This, by far is the best way to test an AGM battery but it requires expensive equipment and the test is involved.
So, all that can be done is to surmise test results using trends & tendencies.
Another home brew test is to make your own tester. Go to an auto parts store and purchase a 100-watt 12-volt light bulb. The bulbs look exactly like the old fashioned 120-volt screw-in light bulbs.
Then go to the hardware store and purchase a round ceramic base that the light bulb screws into. Splurge and buy the type with an on/off pull switch chain.
16 gauge wire is plenty big enough. Cheap battery clips will do fine
After you think the battery is charged. Disconnect charger and hook up the light bulb circuit.
Note the starting time. And the starting voltage of the battery
Switch on the light bulb
Allow it to burn for exactly 8 hours. Then shut it off.
At the moment after shutoff, what voltage do you see? Write it down.
Let the battery sit for six hours. Take another voltage reading. How high is it now?
Recharge the battery.
At 12.8 volts that bulb is going to consume 7.8 amperes
At 12.2 volts that bulb will will consume a theoretical 8.1 amps but the wattage factor is elusive at any but exact voltage.
Tricky? Yes? But this is not a computation of theoretically critical mass for plutonium. It is to allow for a general idea of what is going on.
If you want to, use Mr. Wizards, inductive panel ammeter.
Note starting amperage. Then take amperage and voltage readings hourly and record them.
At the end of 8 hours add up the 8 amperage readings. Then divide by eight.
At the end of 8 hours add up the 8 voltage readings. Then divide by eight.
The divided amp average is then multiplied by eight. This will give you a close-enough AMP HOURS CONSUMED result.
Do the same with the voltage. This will give you an averaged voltage for the test.
MULTIPLY the amp hour result by the voltage average result
This yields total watt hours. i.e. total volt/amp hours.
Mother Fletcher's Do It Yourself Battery Capacity Trends & Tendencies.
WARNING
Folks who would rather watch the Hog Holler 500 Live from Ahuwick, Mississippi, on TV may complain about this reply.
