AGM batteries were first designed to be float life batteries as used by UPS companies and the telco's. So we're always on float (13.6v) with varying current as required to supply the current draw this is why the VRLA lid is important to capture and recombine those gases/water once recondensed back into the batteries acid.
International companies like CTEK, Sterling Power, Enerdrive, RedArc, Mastervolt manufacture chargers that allow solar and either DC charging from an alternator or AC charging from mains supply. The reality is if there was no current being discharged regardless of the charging source (solar or AC/DC) if a battery is floating at 13.6v that's because it's almost fully charged and both devices will within minutes both settle at 13.6v to float charge or maintenance charge the battery. At night the solar controller will be off and the mains charger will finish charging the battery. By the second day the solar controller will turn on as the sun rises, voltage will quickly rise to its pre-set bulk voltage before dropping back to float voltage for the rest of the day. While the solar boosts voltage to its bulk amount the secondary charger depending on the charge algorithm the unit may stop supplying current as it's not in control of the rising voltage to bulk. (the current is what's pushing voltage up, so it regulates voltage at 13.6v but cuts current) But once voltage comes down again and additional current is required it will settle back at 13.6v or float voltage.
We have many auto electrical companies that use, buy and ask our advice.
We have this info to offer:
Auto electricians test their batteries for cranking power, the ability to start the vehicle. Even a battery of only half-life remaining will accept a charge and work off an alternator. A CCA test normally indicates a lack of power which is what is required to turn over an engine. Let's not forget they are used to testing start batteries, alternators, and starter motors and their CCA testers are used to test cranking power and not reserve capacity. Many are also advised on what's needed to test by the battery supplier they are affiliated with. Only if they speak to a specialty product manager within the distribution business will they be given info regarding the requirements to discharge test a battery correctly.
We are also aware of one major distributor only using a 75A discharge current to calculate capacity. Many batteries smaller than 100Ah won't even have technical data to support a discharge of this large capacity so the test results aren't accurate.
You need to visit a marine electrician or a well-trained motorhome service centre to get specific info and ensure it's a discharge test done to industry standards. If the test is free it isn't being done right because it takes time and effort to do this properly and most businesses require payment for their services.