I think you have too much faith in your C-tek's marketing mumbo jumbo( lies)
What voltage is your C-tek holding the battery at?
Through what ambient temperature range? Does it adjust float/maintenance voltage for battery temperature?
Say it floats at 13.4volts always, in Sub 50F temps this is likely too low for an AGM. iin 100F ambients, 13.4v is too high. Sub 50f and the battery will discharge, 100f it will overcharge.
Temperature compensation is very important when there is a wide temperature range the floating battery is to be subjected to.
AGM batteries, I'd rather full charge them and remove charger, as opposed to float them. Reapply charger monthly.
Holding an AGm at the wrong float voltage is not doing it any favors, and AGMS have very little self discharge. Remove the parasitic draws by disconnecting the ground cable when not in use.
Odyssey AGM make some small high quality batteries, but none i see that are the same size as the one you linked.
Not sure how many options you have in that size.
AGM batteries, if they are deeply discharged, are not happy with a 'trickle charge' it tickles them to death.
A 50% depleted 10AH capacity AGM battery, should be fed no less than 2 amps, preferably 3, until voltage reaches 14.4 to 14.7v( assuming a 77f battery)
14,4 to 14.7v should then be held until amperage tapers to 0.05 amps.
An 10Ah Odyssey AGM depleted to 50% would instruct no less than 4 amps be applied until 14.7v is reached at the battery terminals, then hold 14.7v for 4 more hours.
So if your battery is ever depleted to 50% or less, adn not getting this regimen or somewhat close to it via your C-tek, it is not being charger properly, much less kept in 'tip top' shape.
or you can just believe the green light and the charger's marketing and buy another new battery in 2 years or less.
get one of those timers that can activate the C tek for 15 minutes a day and the battery will likely go 4 years.