Think I saw the problem with sudden falling out of the sky this morning.

robport · Feb 15, 2023

I've been flying my Evo II Pro, pretty much since it came out with no problems. This morning, a newish battery I bought last fall during the big Amazon sale, with 12 charges on it, dropped voltage off on the back end like you wouldn't believe. I took off, it read 34 minutes on the screen, battery voltages looked good, so I flew up to about 355 ft to catch the sunrise. After about 10 minutes, I got a battery warning. The screen estimated 4 minutes left. I immediately started dropping altitude, full throttle down and by the time I was at 100 feet, it was reading 2 minutes. I didn't have time to watch the voltages. I got it down, but I could see where someone could have easily flown it until it dropped, which I suspect would have happened if I hadn't been right over the spot where I was and started descending immediately on the warning, which was set at 30%.

MNT DRONE SOLUTIONS · Feb 15, 2023

Bad cell. It's happened to me and Forest landed at the same time it gave me the notification I had absolutely no control. Sadly, it happens quite often.

GeekOnTheWing · Feb 18, 2023

The most-recent firmware update claimed to fix some battery issue. I don't recall the details nor know if it's related to this problem.

mike9591 · Feb 18, 2023

Several things to look for during pre flight especially with older batteries, but great to do the same for newer ones too.
If it is cold outside, warm the battery before flight. Many flying in colder temps will find battery flight time to change abruptly.
Check battery at start up, spin up rotors stay on the ground. Check cells in app
Take off and hover, check cells again for any deviation. 90% of the time a bad cell will be detected here with a cell change of .5 V or more. This same change occurs even faster if the battery is used for a flight. Can go from 4v or so to 3.5 in under a minute.
This is similar for any drone battery. All our batteries here for our work have well over 100 charge cycles, and that happen within about 6 mos given the heavy use. We change them out about every 15 months. Older batteries get moved to jobs that are close range (within 500' of the site). Those are NEVER used over water, urban areas, or forestry.
It should be common practice even after a few minutes in the flight to check those cell levels for deviation. Being prepared for, or using the app voltage indication here and there can save anyone from a damaged battery or emergency landing situation.