On the positive side, it has 4 levels of brightness intensity. In the third position, which is quite powerful, it lasts for 3.5 hours before the battery drains and switches to a lower level, etc. To achieve an eight-hour duration, you will need to have 2 batteries (the purchase price was 78€)

I think it matters how many milliamperes of battery you will use for the time the flashlight will stay on. Take a powerful battery and you will see.

It is the best lens I have ever worked with for professional use.
Many options.
Many hours of operation.

I have this specific Fenix for about 5 weeks.
As for power, it is excellent. Compared to another equally famous one, it is quite lightweight.
Very good in terms of operation options and efficient, especially in combination with Floodlight and Spotlight.
The NEGATIVE aspect is the operating hours (due to my work, it was crucial). At 400 lumens, it worked for 2 continuous hours, then after 4 hours I used it for about 1 hour and it was already flashing for charging, and it worked for another 0.5 hours. So, in the 3 times I worked with the flashlight at 400 lumens, it lasted (with a new battery) for about 2.5 hours.
When it "discharges", it doesn't turn off, but automatically switches to the 8 lumens mode (which is very good).
In the specs, it mentions 21 hours at 400 lumens, NOT AT ALL.
Returning it is unacceptable.
It is not worth its money, it lasts a maximum of 2 hours for PROFESSIONAL use. In case someone needs light for many hours, they should not get it