Aaaaauuuf!
Again... the usual repeated speech with the blinders and now naming the Saturn V, that is completely out of the argument, having no relation at all.
Ok that with additional batteries you can "only" get few more minutes of flight and the motors have to run faster and the drone's maneuverability is partially compromised, etc. etc. ...but say the ultra repeated obviousness (and nonsense) "if you want fly longer, BUY more batteries", cannot be read or hear again!
Someone here cannot realize there are not only those going for simple flights around his garden, or around other locations, not far away from the take-off point, and just for fun, obviously those recommending to buy more batteries belong to this type of simpleton, short-sighted "pilots".
When there is the need to fly several km (or miles) away to reach the target (to be photographed or for other tasks), when you must also ascend a lot in altitude, every single minute added to the flight can make the difference between being able to do the mission and not being able to do it.
Also this should be obvious!
Now please someone doesn't write me flights far away and at high altitudes are illegal and we have to fly at sight, because it would aggravate the tall tale of the many batteries to fly longer.
Said that, just to get new friends...
...I do not say with Phantom 4/4 Pro, the addition of 1 or 2 external batteries is always advisable, but if you replace the DJI props with others having a little more pitch (9.5x6) and you can fly, not too fast, for 3...5 minutes more, well this can be the right way to go when you need to fly longer.
Differently, with Phantom 3 Pro this adding is always advisable and beneficial, as well as a tuning made by many, including me.