Before I get harassed, a few things to consider. I know I was at low battery, I was only flying my Phantom 4 out to do a small loop over land. I was going to prevent auto-land to discharge battery to about 15%, and then continue to hover over my backyard for safety. I only ended up over water due to my aircraft hitting speeds of 37 mph while in P-mode; As soon as I realized how fast I was going I knew something was up and immediately turned around to get home.

Flight Log:

http://www.phantomhelp.com/logviewer/I4LSFXTEEGFIEND5ZC2W/

DJI case analysis (2 weeks in the making):

1. At t=00:19, relative height=68.9ft ,and the aricraft was 62.8ft away from home. Low battery triggered auto landing;
2. Pilot continued to fly unit toward water during auto landing;
3. At t=00:42, unit landed in water.
According to the analysis, the incident was not caused by any product malfunction factors. As such, we could not provide warranty service.


Should you have more questions, please feel free to let me know.
______________________________________________

I went from auto-land function at 20% to dead out of the sky in 23 seconds and this is "not caused by any product malfunction" because I was "flying towards water". This sounds like the most BS way to get out of a warranty. I understand it was risky to fly around with low battery but I had a clear understanding of how the aircraft is supposed to work before the battery just cut out to 0%.

I posted on the forums and the in-detail replies from Phantom users was phenomenal. But when DJI got to my case  they didn’t explain anything that happened to me in my flight logs. Please take a further look into my case and help me figure out how it is my fault that the drone fell from the sky at 18% into water. EVERYWHERE i have read you should be able to prevent auto-land at 18%, but DJI has now informed me that you cannot actually prevent descent at 18% battery.

If you have any questions about the case don't hesitate to ask.

Edit: Forgot to add the picture they sent:  https://mail.google.com/mail/u/0 ... mp;disp=safe&zw

They point to the battery at 0 and the aircraft in the water, but what they fail to explain is how the battery was at 18% before it instantly drained to 0% and free-fell from the sky. I never hit the critically low battery level that would have FORCED a land..
Someone in another forum post also said I might have accidentally switched to sports-mode, but this picture also shows that I was in fact in P-mode.

most of the time I agree with the pilot over DJI, but in this case it appears to me that it's your fault.   

I'm nervous using a battery that's has less than 60% charge, launching with a battery @ 21% is just asking for trouble.   The manual tells you to use a fully charged battery in three different locations.  It sucks and it's an expensive lesson.  

RobSinfield Posted at 2017-6-7 06:06
most of the time I agree with the pilot over DJI, but in this case it appears to me that it's your fault.   

I'm nervous using a battery that's has less than 60% charge, launching with a battery @ 21% is just asking for trouble.   The manual tells you to use a fully charged battery in three different locations.  It sucks and it's an expensive lesson.

I started the flight with 100% battery, I was just doing one last takeoff with 21%, I did not initially take-off with 21% battery. I did read the manual and I do understand you're supposed to take off fully charged. I would never start flying with a partially charged battery

A launch is a launch regardless of previous flights or if the motors were stopped.  Technically you launched at 21% with your battery @ < 3.5 Volts.  At 30 Seconds into your flight the voltage was critical and dropping fast, but you continued away from your home point.  You should be landing your craft between 20% - 30%, preferably closer to 30%.  It's probably a good idea is to show voltage in the app and land before you go below 3.5 volts.

I have read online from dji that you should fully discharge batteries to 15% to maximize battery life. The voltage was dropping fast because my drone inexplicably went way faster than it should have.. in the future I will definitely show voltage on there because clearly the percentage remaining and the estimated life displayed on the app is not a good indicator of how much time you have left to fly

I'm escalating this to the appropriate team in order to have the flight data analysis elaborated. Based on the information provided, though, you will incur stronger wind the higher you go up, it could be within reason that you hit that speed when going with the current. Fighting headwind on the way back will drain the battery faster. Regarding the low battery failsafe, you can adjust the horizontal movement to help avoid obstacles, but you cannot stop it from landing altogether.

Danielfonseca64 Posted at 2017-6-7 07:30
I have read online from dji that you should fully discharge batteries to 15% to maximize battery life. The voltage was dropping fast because my drone inexplicably went way faster than it should have.. in the future I will definitely show voltage on there because clearly the percentage remaining and the estimated life displayed on the app is not a good indicator of how much time you have left to fly

Can you find anything in the manual to suggest you need to or should run the battery down so low?
I can't.
It's something DJI recommended back in the P2 days but not since.
The voltage in your battery tells the whole story.
Flying with such a low voltage is asking for trouble.  
Flying like that over water will always end in tears.

Actually it does say in the battery manual:
"Fully charge and discharge the battery at least every three months to maintain battery health"
At AIRDATA under battery maintenance it is suggested after 20 charges to discharge to 8%.

Eric13 Posted at 2017-6-7 14:31
Actually it does say in the battery manual:
"Fully charge and discharge the battery at least every three months to maintain battery health"
At AIRDATA under battery maintenance it is suggested after 20 charges to discharge to 8%.

Actually, it doesn't.
You may be referring to something old but DJI has not recommended that for quite some time.
Do a word search in these documents to see for yourself:
https://dl.djicdn.com/downloads/ ... y_Guidelines_en.pdf
https://dl.djicdn.com/downloads/ ... ser+Manual+v1.4.pdf

If I remember from the earlier thread, wasn't this the first time this battery had been used?
Taking off with basically a depleted battery, especially if it is it's first usage, is just a bad idea. You should be conservative with new batteries, aircraft, etc until you know how it is going to perform.  I said then and I still say it was pilot error.

Labroides Posted at 2017-6-7 15:43
Actually, it doesn't.
You may be referring to something old but DJI has not recommended that for quite some time.
Do a word search in these documents to see for yourself:

Strange.
I saw this in the battery manual 2017.04 (attached). I guess this is the latest.
Available under this link is 2016.10, it says the same:
https://dl.djicdn.com/downloads/phantom_4_pro/20170125/flight+battery+safety+guidelines/Phantom+4+Series+Intelligent+Flight+Battery+Safety+Guidelines+En.pdf

Your download link relates to an older version from 2016.02.

Eric13 Posted at 2017-6-7 21:46
Strange.
I saw this in the battery manual 2017.04 (attached). I guess this is the latest.
Available under this link is 2016.10, it says the same:

Hmm, they do not seem to agree even between two pages you linked to. On page 2 under Battery maintenance, it is not mentioned. yet on Page 3 under the same title, it is mentioned.

But even so, it is bad advice. "Fully charge and discharge..." is against all the accepted principles of LiPo battery maintenance, because a LiPo should NEVER be fully discharged. If you do discharge it, you must take care not to discharge the pack below the level of 3.0 volts per cell, so for a flight battery, that is 12 volts overall plus a margin, so say 13 volts. For a multi cell pack, discharging below this value may drive one or more cells into negative conduction, irreversibly damaging the cells.
Because the average user doesn't have a clue about batteries, it is far safer to simply let the auto-discharge routine take the battery down to a safe level. The value in doing this is amply demonstrated by what happened when the OP decided to run the batrtery down in the air.

Thanks for all the responses guys. I didn't believe 18% was an over discharge of battery. I now understand the importance of voltage and will always display it on my screen while flying. In response to DJI JAMIE, I was not flying very high and wind was definitely not a factor in the high speeds that caused a rapid decrease in voltage. This wasn't my first time flying a P4 And i have routinely drained the battery to 15% with ZERO problems.. The main issue was the high speeds it reached while already at a low level.. I would never consider going faster than 10 mph while flying below 20%. DJI has yet to explain to me how these speeds were reached. At low battery there should be a maximum speed of 10 mph to prevent a rapid battery/voltage depletion especially considering how smart these drones are.