What to do if you get a Critical Battery Warning in flight and the battery still has lots of mA (power) left.
First of all the Phantom is going to land itself.  Applying full power will slow and eventually stop the decent.
Now the IMPORTANT part.  Press the red circle with the X in it at the left side of the screen.  This will cancel the autoland and restore the flying power curve to the throttle stick.  Bring the throttle stick back to neutral as needed to hold altitude.
It's worthwhile practicing this maneuver.   To practice go to the battery screen in the app and move the critical bat slider from 10% all the way to the right.  Now fly and drain the battery.  When the critical level is approached have the phantom hovering 20' high in front of you.  As the alarm activates put in the throttle, press the red icon.   Remember to reset the critical level when you are finished practicing.
Also don't drain the whole battery as there won't be another warning, you don't want to over discharge it.

Thanks for the emergency procedures practice scenario. I'd add that depending on the environment, P3 altitude, and P3 distance away, the pilot may want to also practice selecting GIMBAL/CAMERA DOWN as part of the procedure or have it set as C1/C2 switch configurations.

The frequent post about crashes due to unexpected behavior, reiterates that "defying gravity" requires that pilots (& hobbyists) plan their flights and be as prepared as possible for the unexpected. It will happen to all of us, the two questions are: "When?" and "Will I be prepared?"

It may also be wise to display and keep an eye on the voltage.

[RCG]Balthazar Posted at 2016-1-13 06:36
It may also be wise to display and keep an eye on the voltage.

You can make the battery voltage display in the upper right corner of the screen, must be set to display from the battery info screen.

Very nice suggestion !