There are times when weather conditions will give you signal problems at about a mile. Happened to hit that one just right. I had 15% battery left when I got back. Too close for comfort.
I've been out 16240 feet and it flew great. Had a spotter for the flight. See no need for me to do it again. Just wanted to see the capability of the aircraft. Stock.
The only thing that can be in the root directory on the card is the bin file. If anything else is there, it can cause problems. If you get a failure, delete everything but the bin file and update again. My updates go smooth as silk when I do this.