Oh, wait: discharge first, then your high-zoot AGM charger will take care of the rest.
Otherwise (without a dedicated AGM charger), discharge first then apply 6 or more amps until 15v (14.6v for a conventional flooded battery), then float the AGM at 13.5-138v.
The thing about the high-zoot AGM chargers is that they are temperature corrected, controlling the amperage and voltage at correct levels through the charge and float phases. SOoooo much easier to use on the AGM. The only requisite is to do the discharge first.
Beginning this thread, I had hoped to learn how to use my collection of conventional battery chargers to maintain the AGM. I learned that, yeah, they'll do it, and give amazing service life from the battery, but the AGM may not be at better than 85% at best.
I'm banking that my Sport's regulator and stator will thank me!