The optimal time to book your ferry tickets to Batam mainly depends on the season, demand, and how flexible your travel plans are:
The peak tourist season of Batam typically extends between February and August, when the island experiences its dry season, with the most favorable weather conditions occurring between June and September. If you plan to travel during these months, we suggest booking at least 1-2 months in advance so you can pick the travel date and time that suit you best.
As for trips in the shoulder season (March to April & September to October) and the off-peak season (November to February), you can normally book a few weeks or days in advance and still find good availability.