The way you're doing it is fine. You can hook up an automatic "battery tender" to it, and just leave it on all of the the time. Most automatic battery chargers will overcharge the battery if left on full time. For the car owners that live further north, it's very important to keep their batteries charged, to keep them from freezing and breaking.
Because the tops of batteries are sealed, now, you can't check the voltage of each cell, so checking the specific gravity of the acid in each cell is one way to make sure the battery charge is adequate, and each cell is good. You can also take voltage measurements of the battery, 13.2 volts is fully charged and I would recharge it when it drops to around 11.5 to 12 volts. A bad cell can mislead you, though, and the battery voltage will be fine until you put a load on it.