Clean all your cables where they connect to the battery and to the frame. Using a multimeter check for voltage while the bike is idling, EFI are usually a constant 14.2v, carbs idling to about 2100 charge near 13.1-13.2 volts above 2000 rpm can go as high as 14.2v. You test thru the pigtail to the tender because it's connected to the battery. One observation, the Deltran smart tenders are calibrated to take the ambient temp in consideration for the charge. The AGM batteries don't like heat. Been in the 90's last few days here.

 

"So, as I said before. Modern Harleys do not have lead acid batteries"

Battery science is exactly the same as it has been for the past 100yrs. There are basically two types of lead-acid batteries. The starting battery and the deep cycle.
An AGM battery is an SLI (starting, lights, ignition) lead-acid battery but a different version. Instead of the electrolyte being a see-able liquid, like a wet-cell battery, the acid is absorbed into the Glass Mat and that mat holds the electrolyte in close proximity with the plates.
The science is exactly the same: plates, lead, lead oxide and electrolyte(mixture of 35% sulfuric acid/65% water.