It's healthy to charge the batteries after each session. When the boat is connected to the charger, its internal ventilation system will activate, removing any potential dampness from inside. You don’t need to worry about the exact percentage during charging—simply leave the boat connected until the batteries reach 100%.
If you plan to store the Quest for a longer period (a few months), it's recommended to charge the batteries to at least 80%. Avoid storing the boat with batteries below 20% for extended periods, and always keep it in a dry environment with a temperature above 16°C.