See my review at:
20 Acres with Drone Deploy
Once battery gets low, the software will beep and show the battery indicator in red. At 25% I hit the home button and brought my P4 home. The manual says to do this, so I don't know what it would do if you didn't. Maybe the quad would land where ever it was at the time?
Eitherway, I didn't move the quad, simply switched out batteries. I went back to my same plan in DD and tapped resume/fly and the P4 took off and went back to the previous waypoint and started from there, so you have some duplicate images.
The one cook feature is that based upon flight time, DD will tell you whether it is a multi-battery operation. You can then adjust altitude or overlap to reduce the mission to one battery. This will equal a lower resolution, however.
My mission was set for one battery at 14 minutes, but with 20MPH winds on the nose, it got to 25% power about 2/3 the way into the mission. No sweat. I finished with 491 images that drone deploy turned into a nice detailed survey.
I have also used it to map custom homes for Landscape architects and the 3D model it produces is pretty nice. However, getting the extra detail is a whole different post. You can see the out come of one on the bottom of my webpage for that services:
Aerial Mapping & Surveys