Mavic went from 96% battery at takeoff to 0%

[ChrisOutdoors]

What was the air temperature when you flew the drone?

 

[boblui]

If I have done this correctly it appears all the cells somehow failed at the same time and magically recovered. I have never observed that with a lipo battery pack. Could dirty battery terminals cause this?

In the other very similar case the battery behaved in the same way so I believe it's just the characteristics of the battery. ie, it degrades suddenly instead of gradually. Flying with battery like that is very risky.

I haven't come across any data but my understanding has been that the BMS keeps monitoring the charging and discharging process of the battery, work out the latest battery capacity from the data and use that up-to-date capacity as the base for calculating the battery % figure. This adjustment done by the BMS can be seen if you upload the flight log to Airdata.

In this case the battery capacity calculated by the BMS was reduced from 2136 mAh to 184 mAh during the flight. I would expect that the BMS will memorize the 184 mAh capacity figure and use that as the base for computing the battery % figure in the next flight. The % figure will drop rapidly from 100% to 0% in very short time but the drop will be roughly linear instead of a step drop in the middle. Unfortunately the drone is now at the bottom of a lake so that cannot be proved.

 

[sbell1967]

What was the air temperature when you flew the drone?

Around 55 and wind around 5MPH. In other words, rather perfect weather for flying.

 

[boblui]

I am just wondering if you can provide the flight log file for the previous flights that use this battery ? It will help to determine whether the degradation can be seen in advance or it's just something that cannot be avoided.

 

[JackL]

In the other very similar case the battery behaved in the same way so I believe it's just the characteristics of the battery. ie, it degrades suddenly instead of gradually. Flying with battery like that is very risky.

I haven't come across any data but my understanding has been that the BMS keeps monitoring the charging and discharging process of the battery, work out the latest battery capacity from the data and use that up-to-date capacity as the base for calculating the battery % figure. This adjustment done by the BMS can be seen if you upload the flight log to Airdata.

In this case the battery capacity calculated by the BMS was reduced from 2136 mAh to 184 mAh during the flight. I would expect that the BMS will memorize the 184 mAh capacity figure and use that as the base for computing the battery % figure in the next flight. The % figure will drop rapidly from 100% to 0% in very short time but the drop will be roughly linear instead of a step drop in the middle. Unfortunately the drone is now at the bottom of a lake so that cannot be proved.

Wow that thread is very informative, along with this one as well! Thank you.

I am going to review all of my flight logs for battery performance now and most certainly purchase at least two more batteries which I will also now also obsessively monitor!

 

[sbell1967]

I am just wondering if you can provide the flight log file for the previous flights that use this battery ? It will help to determine whether the degradation can be seen in advance or it's just something that cannot be avoided.

Unfortunately it's been awhile since I flew, and I'm using a new tablet that doesn't have previous flight logs.

 

[DanMan32]

Called DJI today to see what can be done without retrieving the drone (since I have all the flight data, plus the screen recording of my flight from my tablet).
They can only create a case and look at the data if it was under the 1st year of the manufacturers warranty. I'm on my 2nd year of Refresh and they won't even look at it. And of course my Refresh expires tomorrow...so basically I'm screwed.

In order to have a second year of Refresh, you would have had to have bought Plus. Plus extends the warranty, not just the Refresh for the entire term.

That's why I've been recommending buying Plus within 6 months of drone purchase and after the prerequisite Refresh purchase, as some components are only warrantied for 6 months.

 

[boblui]

Just want to ask a question. about the BMS, the small computer inside the battery. Is there anyway to detect a problem with the battery before failure.
I have had one battery for four years now, and have it marked to keep a eye on it. But no idea as to what to look for, as advance warnings about BMS failure. I try to prevent things from happening, like with my motors, checking temp of each motor. Recording temp of each motor, turning the prop by hand to feel or hear any strange noises ETC. Any body have any preventive info to share please?

I would suggest a few things :

1) Discharge the battery fully every 3 months as instructed by the DJI user manaul. This is to let the BMS to know the end point of the discharge curve so that it can be updated on the latest battery capacity.

2) Update to the latest battery firmware.

3) Upload the flight logs to AirData and check the discharge curve. This is a comparison I have done in my reply to the other thread on similar problems. The curves for the healthy battery are in blue and the problemetic one in red

 

[sbell1967]

Quick update. After calling DJI support and not getting anywhere (call taker didn't even see I bought Refresh Plus in the 2nd year), I emailed support, attaching my flight logs and flight record from the tablet I was using. Even included the video of the screen, showing all the necessary data.
Again, the drone warranty was expiring 2 days after the crash.
Lo and behold, someone from DJI got back to me. I need to sync the flight records and again, sent in all the necessary data and then some.
Through multiple emails and analyzing the logs, they determined that it was definitely a hardware failure, and I did NOT have to recover the drone.
Today I received my brand new Mavic Air with a new battery as well.
Thank you so much to DJI for hearing me out and coming through in the nick of time.
Lesson learned...won't be talking to phone support again, e-mail worked best for me.

 

[Thomas B]

Quick update. After calling DJI support and not getting anywhere (call taker didn't even see I bought Refresh Plus in the 2nd year), I emailed support, attaching my flight logs and flight record from the tablet I was using. Even included the video of the screen, showing all the necessary data.
Again, the drone warranty was expiring 2 days after the crash.
Lo and behold, someone from DJI got back to me. I need to sync the flight records and again, sent in all the necessary data and then some.
Through multiple emails and analyzing the logs, they determined that it was definitely a hardware failure, and I did NOT have to recover the drone.
Today I received my brand new Mavic Air with a new battery as well.
Thank you so much to DJI for hearing me out and coming through in the nick of time.
Lesson learned...won't be talking to phone support again, e-mail worked best for me.

Way to go! Congrats on the result of your persistence.