I am guessing that you live in a high elevation area. Sadly where I live, the highest mountain is around 4,000 feet and it's off limits to the public. If not I would have loved to go there and do testing for you. If you already own a Tello, your best bet is to take off and let it hover until it uses the battery and lands. Take the time and we can do the math to calculate how much time you lose with altitude. I can confirm that the battery lasts 12 minutes 58 seconds of flight time at sea level.Thanks. I searched a lot of sources but come up empty when I try to find the "service ceiling" for the Tello.