there are quite a few complaints about battery life and how some think that DJI advertises overly optimistic numbers.

Doesn't dji (and all drone manufacturer) advertise flight time not only as under optimized conditions but also as flight time till the drone shuts down? Call it a no reserve battery life.  I usually land it with 20/25% battery left and get 12 minutes of usable flight time or so... that's pretty much 15/16 minutes if I was using 100% of the battery.

As to flight conditions and how it affects flight time, they have to use an average which would be moving and hovering in place which uses more power. Publishing a hover only time would be just as meaningless as car manufacturers advertising only in town fuel mileage.

Common sense dictates that any manufacturer number, whether drone, cars, boats, airplanes, phones,... will always be under best conditions.

Dji post a flight and hover time:

Max Flight Time
16 minutes (no wind at a consistent 12.4 mph (20 kph))

Max Hovering Time
15 minutes (no wind)

http://www.dji.com/spark/info#specs

coz its done in a controlled enviroment...

I have no complaints personally about battery life.  As stated above, I expect the spec/numbers to be highly optimized.  I'm getting about 10 minutes of flight when I get the 30% battery warning, and I'm pretty consistently landing when I receive that warning.  Since I put on the propeller guards all the time (adding weight), 10 minutes seems about right.

If you look at the logs of your flight and see the voltage of the three cells you will see that there is plenty of Juice Left. LipoCritical voltage is 3 volts per cell , I bet you want hit the tree volt mark even on 0% . It is advised not to discharge fully LiPO batteries ,but if one in a 10 Times you will discharge it fully it will not be damaged as it won't get below 3V

We had the specifics of the max flight time and max hovering time in a certain condition, different flight environment and use of the sticks may affect the flight time. So it always depends on where to fly and how to fly.

Szwedu Posted at 2017-8-4 07:50
If you look at the logs of your flight and see the voltage of the three cells you will see that there is plenty of Juice Left. LipoCritical voltage is 3 volts per cell , I bet you want hit the tree volt mark even on 0% . It is advised not to discharge fully LiPO batteries ,but if one in a 10 Times you will discharge it fully it will not be damaged as it won't get below 3V

Here you go , someone tested his battery. Look at cell voltage
By 0% you get a healthy 3,5 VOLTS
its more than good at 0%
http://www.phantomhelp.com/LogViewer/8NZP5H7A3ZSE46R1PWGT/