All the batteries that I've had in the past had the acid shipped separate and had fill ports. This one doesn't.
One concern is that I have no idea how long it sat with acid in it and I've been told that the separate ones have a very, very long shelf life because the acid isn't in it.
It also has a charge, but I don't know how strong. On the 10a charger, it's fairly strong, so do I do a slow charge with a 1 amp for a few hours?
I really can't see any advantage to them having the acid already in it. No telling how long it's been on a shelf. I guess I'll find out how long it lasts. Last one was about 5 years.
I suggest doing a slow charge until it is fully charged.
As a check before commencing the slow charge, I also suggest doing a voltage check, the number will be of some insight as to the present charge status of the battery.
I used the link you provided.
I see it's a AbsorbedGlassMatt type battery, thus explaining the factory fill instead of fill at time of first use.
I don't know much about AGM batteries, but the "absorbed" and "matt" words strongly suggest to me that the manufacturing process requires that the electrolyte be added as part of that process.
Classic plate batteries have their plates "immersed" in electrolyte and the space between the plates is where 99+% of it resides.
AGMs don't have large volume voids for the electrolyte, and my guess is that the word "absorbed" actually means weeny teeny pockets of electrolyte within the glass matrix, with a higher percentage of the total electrolyte volume being in direct contact with the anodic and cathodic materials.
I'm not at all surprised that there are no fill or top up plugs, as they don't sound to make sense given the design nature of the battery.
(as an aside, the use of high purity lead, especially antimony purged high purity lead, in classic lead acid plate batteries negates the need of water top ups over time - overcharging considerations ignored that is)