SQLiteDataBase one instance, and open/close for working with my SQLiteDatabase?

I have on my MySQLiteManager class with Singleton pattern one MySQLiteOpenHelper object, so like my MySQLiteManager cant only be instantiated one time, my MySQLiteOpenHelper object will be only instantiated one time too.

I don't know if it's better to have one OpenHelper object or one instance of myhelper.getWritableDatabase() and open/close it for use it correctly on different activities, or it's better call getWritableDatabase() each time that i need read/write.