IMO , first you should not wait to be out of battery to land. Waiting until 1 light , and the tail flashing red is asking for trouble. Then triggering an RTH force the P2 to go up to 20meters, fly back to you and land. It may not have enough power anymore to do that, receives 2 contradictory informations, one for landing on low batt, the other to climb, go to home point and land, or the inverse, depending on which one came first. Mine as well get kind of mind of its own when too short battery. Stay safe and land when it just starts to flash red on throttle, at 2 battery lights flashing...