If truly limited to 800 mA, that is a "maintainer", not a "charger".
If it has spring clamps, it is not ABYC compliant.
Even an 800 mA maintainer with spring clamps, can create a spark in a battery compartment.
Any combustible, such as hydrogen gas from a charging battery, gasoline from an improperly stored jerry, stove alcohol from a leaking jug, propane from a canister, tank, or chafed hose, can cause a "kaboom" or fire.
The spark isn't the problem if there's nothing to ignite. This holds true in automotive diagnostics as well.
Unless the battery gasses, which a healthy AGM, charged slowly, won't do. My only other combustion source is the propane tank, which is in it's own isolated compartment, with the valve closed for the winter.
As I said, I'm not concerned. The batteries and charger are coming in soon, So once I figure out how I'm going to place and mount the batteries and bus bars, I can get the 48v-12v converter and install that part of the system in the boat. Then I'll trade all the lead-acid peccadilloes for lithium peccadilloes. Which, to my mind, are much more manageable.