Ok guys, i will try to explain the complete test i'v just done 2 months ago. ( i wish i think of capture that on tape !!)
Was done on a brand new unboxed P3P
Here i don't talk about voltage view of the lowest cell on the battery, i think it the best way to know if it's time to get back to land or not,
anyway...
full 100% battery (flying for fun for couple of minutes)
then, 30% battery, warning message "low critical" and sound beeping.
then 20% battery, popup that say it's better to land you bird (you can cancelled that message on screen)
then 10% battery, a voice telling you it's going to land now and the bird start to descent.
you can trigger up the left stick and fight that landing until 0%
and then...
0% battery , the bird will go dead drop (4 motors stopped), believe me i'v try it from 2 feets above the ground on a safe grass.