Car batteries are far more tolerant of charge currents than MC batteries. It is a matter of scale. Car batteries have about 5 times the power factor of MC batteries. The bigger lump is more tolerant of "abusive" charging levels.
If the MC battery has been "float charged" at levels appropriate for a car battery, it likely has abusive levels for a MC battery. Can't say for sure without doing measurements. And, the HF link does not list any charger specifications for proper analysis. But, overcharging commonly begins the electrolysis process on the electrolyte, which separates hydrogen and oxygen from the solution in gaseous form. H2O is water. Or, it was when it was still combined with the sulfur in the electrolyte (H2SO4). If you remove the water from the battery it goes dry and stops working. Batteries can't live on sulfur alone.
The battery can go dry from overcharging, or neglect at keeping the electrolyte topped up with distilled water. Hydrogen and Oxygen are liberated from the electrolyte solution both during charge and discharge conditions.
If you find the battery dry, fill it enough to cover the plates with distilled water and see if a charger will bring it back to some usefulness.
Measure the voltage and if it goes above 12.8 V, it may just revive. If not...recycle instead of land fill.
Cheers,