Mavic went from 96% battery at takeoff to 0%

sbell1967 · Dec 22, 2020

Anyone have a good answer for this? Took off, battery was at 96% when I lifted off, ran about 1,000 feet out and I think about 250'. Then all of a sudden I get a critical battery warning and a RTH warning. Then the battery dropped to 0% and it autolanded. Right into a F^%^#$!! lake.
TXT and DAT files attached for your amusement.

Thomas B · Dec 22, 2020

My only experience like yours was with a battery in my M2P. It was caused by a failed cell.

Deleted member 103366 · Dec 22, 2020

How 'old' was the charge on the battery?

One thing I did notice is that if I use CsvView charts to look at some of the battery data from DJIFlightRecord_2020-12-22_[13-46-17] quite a few entries/signals are "empty" i.e. CNTR_BATT:currentcapacity [mAh]
CNTR_BATT:fullcapacity [mAh]
CNTR_BATT:relativecapacity [mAh]
CNTR_BATT:errorType
CNTR_BATT:currentPV [V] (didn#t realise I tried this one and have no idea at the moment what it is).

I have NO IDEA if that is normal for the MA etc. but thought it curious

sbell1967 · Dec 22, 2020

PhiliusFoggg said:
How 'old' was the charge on the battery?

One thing I did notice is that if I use CsvView charts to look at some of the battery data from DJIFlightRecord_2020-12-22_[13-46-17] quite a few entries/signals are "empty" i.e. CNTR_BATT:currentcapacity [mAh]
CNTR_BATT:fullcapacity [mAh]
CNTR_BATT:relativecapacity [mAh]
CNTR_BATT:errorType
CNTR_BATT:currentPV [V] (didn#t realise I tried this one and have no idea at the moment what it is).

I have NO IDEA if that is normal for the MA etc. but thought it curious

I just charged the batteries last night. I looked at the flight record on my tablet and it literally went from 86% to 0% in a heartbeat. There was no way I could have recovered from it. I don't think I could have even enabled sport mode, since the forward motion was limited by the battery depletion, and I was already travelling at 18MPH.

Deleted member 103366 · Dec 22, 2020

Ignore the point about empty signals, I have just started going through an M2 log and it is similar.
There is a precipitous drop in in what might be indicated battery capacity in the DAT data around the 88sec. We will have to wait and see what the gurus think

Thomas B · Dec 22, 2020

PhiliusFoggg said:
Ignore the point about empty signals, I have just started going through an M2 log and it is similar. There is a precipitous drop in in waht might be indicated battery capacity in the DAT data around the 88sec. We will have to wait ans see what the gurus think

Agree... but I’m betting on a battery cell failure presently.

Meta4 · Dec 22, 2020

sbell1967 said:
I looked at the flight record on my tablet and it literally went from 86% to 0% in a heartbeat. There was no way I could have recovered from it.

The important thing to look at is the cell voltages for the battery.
The % indicator will give misleading information for batteries with problems.
The Phantomhelp log viewer summary report from your txt file will show cell voltages for the whole flight.
But there's a problem with the website and it's not opening any files at the moment.

JackL · Dec 22, 2020

It almost has to be a catastrophic cell failure, unless some circuitry inside the battery could actually cause this situation which seems really unlikely. That is my worst nightmare situation since I mostly fly over the ocean.

sbell1967 · Dec 22, 2020

JackL said:
It almost has to be a catastrophic cell failure, unless some circuitry inside the battery could actually cause this situation which seems really unlikely. That is my worst nightmare situation since I mostly fly over the ocean.

And of course my DJI Refresh is no good without a body ?

Thomas B · Dec 22, 2020

Meta4 said:
The important thing to look at is the cell voltages for the battery.
The % indicator will give misleading information for batteries with problems.
The Phantomhelp log viewer summary report from your txt file will show cell voltages for the whole flight.
But there's a problem with the website and it's not opening any files at the moment.

The site is functioning now it seems:

DJI Flight Log Viewer | Phantom Help

Upload and view flight logs from your DJI drones

www.phantomhelp.com

JackL · Dec 22, 2020

sbell1967 said:
And of course my DJI Refresh is no good without a body ?

It is too deep to freedive?? Contact the local scuba club and see if anyone is interested in rescuing it. Might get lucky.

I have been looking at getting these (getterback.com) devices to make a water recovery hopefully a little easier.

sbell1967 · Dec 22, 2020

Thomas B said:
The site is functioning now it seems:

DJI Flight Log Viewer | Phantom Help

Upload and view flight logs from your DJI drones

www.phantomhelp.com

Site is still down. Times out while trying to upload the log.

Thomas B · Dec 22, 2020

sbell1967 said:
Site is still down. Times out while trying to upload the log.

:-(

JackL · Dec 22, 2020

So the log site being down made me go ahead and install Datcon. I do not see individual cell readings in the .csv. Battery sure does what he said at 86%. Beyond that I only understand a little of what is in this file.

e understand this screen?

Thomas B · Dec 22, 2020

Hopefully the site will be back up soon. I still believe the event was a battery failure... and not fixable.

JackL · Dec 22, 2020

Ok I think we can safely assume it had a catastrophic battery failure.

DanMan32 · Dec 23, 2020

sbell1967 said:
And of course my DJI Refresh is no good without a body [emoji53]

But it can be a warranty issue. You don't need a body if the mobile logs show a system fault, as long as warranty is in effect. That's why I recommend getting Plus within 6 months of purchasing the AC and after having purchased Refresh. It extends the warranty.

Meta4 · Dec 23, 2020

JackL said:
Battery sure does what he said at 86%.

The battery % indication commonly shows misleading or even meaningless information.
Until the cell voltages are visible, it's not possible to know what really happened.

boblui · Dec 23, 2020

I have taken a look at the log and I am not sure whether the drone was drawing too much current or the battery was faulty. If you can provide the log of normal flights in the past, the reason can be established with better certainty.

My observation :

The starting cell voltage was 4.2V which is very normal for fully-charged LiPo battery but it dropped very rapidly to around 2.8V after flying for just 90 seconds. For my M2, the battery % hit zero when the voltage dropped to 3.6V so 2.8V is abnormally low and should not be reached in normal operation.

Usually it means the battery is bad but as soon as the drone went into autolanding and the current reduced, the voltage bounced back to a very healthy level of 3.8V.

So what's wrong ? Was the voltage drop caused by the current being excessive or there were some problems with the battery ? I am not sure.

Just a few more words on why the battery % dropped from 86% to zero in no time. The battery capacity detected by the BMS ( Battery Management System, a small computer inside the battery ) at the beginning was 2136 mAh which is reasonably close to 2375 mAh stated in the spec so no problem there. As the battery is discharged, the BMS integrated the current with respect to time to come up with the no. of coulombs ( or mAh ) taken out of the battery and used that to calculate the battery % figure. At the same time, the BMS was monitoring the battery voltage for the purpose of updating the battery capacity - a process known as battery calibration.

When the voltage hit 2.8V, the BMS decided that the battery has unexpectedly fully discharged so it reported 0% to the flight controller. Base on the cumulative amount of mAh delivered by the battery, it re-calculated the battery capacity and came up with 184 mAh.

It is also noticed that the current drawn by the four motors were very different, not sure if that's normal but I don't want to confuse you with these fine details .....