The app assumes the battery is fully charged at the beginning of the mission.
However, it does not take into account the battery that is necessary to reach the first waypoint of the flight and to fly back from the last waypoint The warning pop-up displays safety instructions that are specific to each drone.
If you wait until after your gear is stolen, you'll have to add the gear, verify it with something else other than a picture of the serial number and wait a day or two for someone at Lenstag to approve the verification request.
By then the gear has probably been pawned or sold and the chances of successful recovery are substantially lower.
Press "Add To Shelf." Once you add content to your shelf, you'll be able to view it as full-text page images.