You can basically just leave a battery connected to the battery charger, provided it is a so-called trickle charger.
A trickle charger is an intelligent battery charger that provides the battery with just enough current to stay fully charged without damaging the battery. Battery chargers without a trickle charge mode can potentially damage the battery by “overcharging” it.
So if you use an intelligent battery charger that automatically switches to trickle charging, you can leave the battery connected to the charger without any problems. Read more about how to charge a battery here.

This month was THE boat reveal of TU Delft’s Hydro Motion Team and we are proud battery sponsors there. See below the boat the students designed themselves, which contains the battery.