Hi Guys,
After having Mavic in 2017, I got MAVIC 2 PRO on october 2018. I have been very happy to use it untill today... I planed to record some floods on Loire river in France. Wheather fine with sun.
At 10h55:36  I took off...check everything .. and go slowly rising to 70 meters high at 200 meters far or so. At 10:56:11 "WARNING BATTERY dangerously low. Mavic force to immediate landing". 10h57:20 "WARNING low signal" and then LOST signal (probably in the flood).
I got these infos on "ERROR_POP_LOG" but I am unable to read other files on my Mac. Some are .log, some others .text and some .dat. With DJI Assistant 2, I exported to my mac the file "DJI_ASSISTANT_EXPORT_FILE_2021-02-07_17-58-11" but unable to read.
Does anyone able to help me undestanding what exactly happened.
Just now, I can't believe a fully charged battery can discharge in less than 1 minute. So maybe there has been a short circuit or a bad sensor or information from the battery.
Thanks for what you could do.
Jean

Upload your flight record to the following site and I’m sure you’ll get many people here that will help you interpret them.  https://www.phantomhelp.com/LogViewer/Upload/

Hi Jean, sorry to hear about your drone. I read somewhere about problems with batteries from last quarter of 2018. The text file will tell what happened. If you have any more batteries from that time, check them out and also if they are swollen, if so do not fly with them.

KlooGee Posted at 2-7 10:32
Upload your flight record to the following site and I’m sure you’ll get many people here that will help you interpret them.  https://www.phantomhelp.com/LogViewer/Upload/

Great !  Thank you. I got it .
Here is the link to my log <https://www.phantomhelp.com/LogViewer/305H0TD2YCY7YJXTK8ML>
The very strange thing is that my battery dropped from 92% charge to 0 in 1 second. And  just last week an other battery bought on october 2018 got swollen. Bloody hell. A serious issue from DJI.

Hello, sad news about your drone...

I use at the moment 2 batteries for my M2P.  I bought them practically together.  The batteries are used in sequence, which means their charging/discharging amounts is quite identical.  As soon as I would notice anything suspicious on one of these batteries, they will be replaced both immediatly.

I understand, that of course, it is easy to say this now...  

If you have an unlucky day, and one of the cells fails, there is nothing you can do...

But in the screenshot you have posted, you can already see a big difference in the voltage of cell1 compared with the other cells....

JEAN C Posted at 2-7 11:14
Great !  Thank you. I got it .
Here is the link to my log
The very strange thing is that my battery dropped from 92% charge to 0 in 1 second. And  just last week an other battery bought on october 2018 got swollen. Bloody hell. A serious issue from DJI. [view_image]

The very strange thing is that my battery dropped from 92% charge to 0 in 1 second.
You have to look at the cell voltages rather than the % indicator.
When the battery  has been self-discharging for a while, the % indicator will give a false reading.
Your battery had cell voltages below 3.2 volts (critical low voltage) within 30 seconds.
It was not fully charged at launch time.

Labroides Posted at 2-7 13:36
The very strange thing is that my battery dropped from 92% charge to 0 in 1 second.
You have to look at the cell voltages rather than the % indicator.
When the battery  has been self-discharging for a while, the % indicator will give a false reading.

Thanks, Captain.
This battery was FULLY charged the night before, with the genuine DJI charger and without any further information. Since the charger switch off when the battery is FULLY charged, I can't suspect any problem. Obviously, there is something wrong between the supposed INTELLIGENT battery and the software who decide to land down to the flood in 1 second.

JEAN C Posted at 2-7 14:37
Thanks, Captain.
This battery was FULLY charged the night before, with the genuine DJI charger and without any further information. Since the charger switch off when the battery is FULLY charged, I can't suspect any problem. Obviously, there is something wrong between the supposed INTELLIGENT battery and the software who decide to land down to the flood in 1 second.

Obviously, there is something wrong between the supposed INTELLIGENT battery and the software who decide to land down to the flood in 1 second.
The cell voltages tell the story.
You might have had it on the charger, but the battery was not fully charged when you launched.
It was already out of gas.

Hello there Jean. I am sorry for the trouble this has caused and thank you for reaching out. Since this unfortunate event happened to your DJI Mavic 2 Pro. It would be best to contact our DJI Support Team for further assistance. You may contact or DJI Support Team at : https://repair.dji.com/repair/index or via http://www.dji.com/support to open a case. Again, I am sorry for the trouble and thank you.

JEAN C Posted at 2-7 11:14
Great !  Thank you. I got it .
Here is the link to my log
The very strange thing is that my battery dropped from 92% charge to 0 in 1 second. And  just last week an other battery bought on october 2018 got swollen. Bloody hell. A serious issue from DJI. [view_image]

Hi,

I have had a look at your battery cell values, see my chart of your data.

So at takeoff 4 cells > 4.1 volts. (96%), meaning that if you had check the voltages in the app ; you would not be alarmed at all.

The moment celll1 drops below 3.2 a message in the log > BattTempVoltageLow.Temperature did not help ofcourse with batt performance, but not all 4 cells but just 1 cell  is faulty.
When cell1 volts drops below 2.6 volts > total indication from 92% into ZERO volts > critic error = autolanding.

Conclusion : faulty battery, cell1 is the faulty one.
Could you have notice this before?  yes, but only if after each flight you check the batt cell values for the whole flight.
A faulty cell will normally slowly become more and more offset to the good cells.

Second chart is an example of 1 flight with a MP as well, easy to check cell values during flight  (84 - 46%)

cheers
JJB

Hi Captain,
Thank you for all these explanations. I never noticed any weakness before  on this battery bought on october 2018 with 2 others. I have never given a special name to each of the 3 batteries, but I always used them equally, one after the other. A strange thing is that, just a week before, one was swollen and I discarded it. So that means 2 batteries collapsed at almost same time, after 2 years use, without any warning before. I am also surprised that the Mavic immediately landed on flood instead of returning home at only 160 meters far. Anyway, I filled a claim to DJI support and I hope they can do something for me. I also hope that other pilots will be aware of such problem and detect it as soon as possible.
Last question : "after each flight you check the batt cell values for the whole flight" How can I do it ? I have only 1 battery left, looking OK, but I ll be afraid to use it now.

JEAN C Posted at 2-8 01:44
Hi Captain,
Thank you for all these explanations. I never noticed any weakness before  on this battery bought on october 2018 with 2 others. I have never given a special name to each of the 3 batteries, but I always used them equally, one after the other. A strange thing is that, just a week before, one was swollen and I discarded it. So that means 2 batteries collapsed at almost same time, after 2 years use, without any warning before. I am also surprised that the Mavic immediately landed on flood instead of returning home at only 160 meters far. Anyway, I filled a claim to DJI support and I hope they can do something for me. I also hope that other pilots will be aware of such problem and detect it as soon as possible.
Last question : "after each flight you check the batt cell values for the whole flight" How can I do it ? I have only 1 battery left, looking OK, but I ll be afraid to use it now.

HI Mate,

You did charge the battery the night before and it was correctly fully charged.

How can I be certain? because the battery will blink at you to advise it has a bad cell when you charge it.

Also if you have a bad cell that is one that is just a fraction below the other cells voltage the app will not let you take off. It will say battery error.

The first warning you got was to warn you that the battery was too cold. You should have landed immediately.

One cell failed due to the cold. At that point as all cells are connected in series you had 0% battery left even though other cells were good. It's the old weakest link story. Like blowing a fuse.

Hi
"because the battery will blink at you to advise it has a bad cell when you charge it. " NO the battery didn't blink at me meaning there was a bad cell. The charger just switch off the charging light on the battery, meaning the full charge. I am certain ! You 're right : No warning at the start and taking off fine until 1 mn : strange ! The outside temperature was about 6 to 7°C, not very cold. Since the Mavic was only 103 m away, there was probably enough power to return gently,  instead of going forward from 103 to 162 meters and landing slowly into the water ! Bad emergency decision !

JEAN C Posted at 2-8 01:44
Hi Captain,
Thank you for all these explanations. I never noticed any weakness before  on this battery bought on october 2018 with 2 others. I have never given a special name to each of the 3 batteries, but I always used them equally, one after the other. A strange thing is that, just a week before, one was swollen and I discarded it. So that means 2 batteries collapsed at almost same time, after 2 years use, without any warning before. I am also surprised that the Mavic immediately landed on flood instead of returning home at only 160 meters far. Anyway, I filled a claim to DJI support and I hope they can do something for me. I also hope that other pilots will be aware of such problem and detect it as soon as possible.
Last question : "after each flight you check the batt cell values for the whole flight" How can I do it ? I have only 1 battery left, looking OK, but I ll be afraid to use it now.

Hi Jean,

I use FRAP, its a analyse tool for flightlogs.
In this program you can check battery values each flight, save the last 10 flights with batt history.
So easy to see if a battery slowly gets bad performance. (charts are from FRAP in my post)

It is a choice made by DJI to autoland drone when battery gets below certain value!  IMO an controlled autoland is safer than fly back and dropped out of the sky!

https://forum.dji.com/forum.php?mod=viewthread&tid=203659
cheers
JJB

Battery may have come loose. This may explain catastrophic drop in voltage. See my post in another forum where i was lucky. Thread 'Battery Falling Out':
https://mavicpilots.com/threads/battery-falling-out.106211/
This forum does not allow for clickable links. You'll need to copy and paste link url into browser.

Hi JJB,
Thanks for your advice about FRAP. Unfortunately, I am using a Mac... I checked about my last available battery (from the set of 3 bought in october 2018). Here is the analysis of the flight I did just before the crash with another battery.
<https://www.phantomhelp.com/LogViewer/M3TNJX19HFNDIML03CAR/>.
The cell 4 dropped during 1 second and then 2 others during 1 and 1 second; and then cell deviation became critical for 1 second again. And then every cell rise up to become normal again. No message appeared to me. Do you thing that kind of fancy incident happens often ? Or do you think I should discard that battery too ? With t Flight Log Viewer, I can be aware of future problems, no ?

JJB* Posted at 2-8 01:24
Hi,

I have had a look at your battery cell values, see my chart of your data.

Many thanks JJB for the valuable and excellent information about this: "Could you have notice this before?  yes, but only if after each flight you check the batt cell values for the whole flight."

JEAN C Posted at 2-8 06:33
Hi JJB,
Thanks for your advice about FRAP. Unfortunately, I am using a Mac... I checked about my last available battery (from the set of 3 bought in october 2018). Here is the analysis of the flight I did just before the crash with another battery.
.

hi, bad luck to be a mac  user   ;-)

Battery values looks oke to me, at the end of the flight normal equal values.
Cell deviation under load (large RC inputs etc, or sport mode) are 'normal' as long as they are not too large.
And 125mVolts is not that bad, seen much higher values for battery under load.But many opinions on what is NORMAL for max deviation!

But guess i will replace my battery after few years of usage, better safe than sorry.



cheers
JJB