Hi
I have a question about when I am doing the maximum distance flight test of my Mavic 3.

The question is
If I start the video recording by using the drone’s camera from the flight begin. Will it run out the drone battery faster, when compare to not using the drone camera to recording the whole flight test video from the begin?

If yes, should I just use the screen recording from iPhone to record the whole process?

Hope someone can help me to figure out this question

In so many words, yes. If you go for endurance flight, you don't want to record video, or waste juice on obstacle detection.
To be honest, I don't think the difference will be huge, as there are so many other important factors, but yeah, record on the screen.

i think recording impact on  flight will be negligible, but why relly on others - make Your own test with And without recording and share Your findings - i personally always record even during such flights

Yes it will impact your battery percentage not really sure as to how much but anything such as: obstacle avoidance, shooting video, tele-lens, led light, and I don’t know for sure but maybe also air sense not sure but all these will impact your battery life.