There are two types of chargers.
One type puts out amperage constantly while the other type senses the condition of the battery and cuts the amount of charge back as the battery gets close to full charge.
Overcharging a battery will ruin it so you should use a charger that is "regulated".
Owning a simple hydrometer will tell you what the state of charge is in each of the six cells. Buy one, learn how to use it and then check your battery before you charge it and then afterward. Right down the readings so you don't forget. If one cell stays at the same specific gravity, then that battery is on its way out. You may get the summer season out of it but come next fall, a replacement would be a good move.