Hi all
I probably should not own a drone....
My Spark went swimming a couple of weeks ago (https://forum.dji.com/thread-178398-1-1.html). Nevertheless I decided to get another drone, this time a Mavic Air. Bought it used, about 9 months old. Today I went for my first flight, everything went just fine. A couple of hours later I took it for another flight, using another battery. This time things did not go that well.

Flight record here: https://www.phantomhelp.com/logviewer/8KLT5DTF3VFJ33E6PS2Y/

As you can see there are som cell deviations early on and then after about 50 seconds in the air the battery goes from 82% to 0%. It initiated a forced landing, fortunately missing the roof of that nearby house, however it crashed into something and flipped over on the way down in that backyard it decided to land in. After the crash I was promted to do a compass calibration, but after that it seems to work fine again. Started it up and hoovered for a few seconds without issues.
When checking the battery level just after the crash it seemed empty, with only one led flashing. However, when I started charging it at home it almost immediately went into 2 led with steady light and the 3:rd flashing. Seems like it was not that empty after all.

Now I have a few questions:

1. Do I have a bad battery (hm, obviously) or could this have happened for any other reason? The weather was a bit cloudy, about 0 degrees celsius.
2. Could I have aborted the forced landing? To land it manually in an open space instead.
3. Could I have avoided this by doing some pre-flight checks?
Edit: Batteries have 32 and 28 charging cycles respectively.

I will not trust that battery at all. Its brain went coo coo. At the start the cell voltages suddenly dropped to 3.5v, that is already at the 20% level more or less.

Was the battery fully charged? Or why was it at less than 90% at startup?

As far as I know you cannot abort landing by throttling up when the battery is at critical low level.
What were the battery temps at startup? did it warn you about a cold battery?

Koelkop Posted at 1-29 11:21
I will not trust that battery at all. Its brain went coo coo. At the start the cell voltages suddenly dropped to 3.5v, that is already at the 20% level more or less.

Was the battery fully charged? Or why was it at less than 90% at startup?

More or less fully charged. I just got the drone today and I didn't charge the battery myself but confirmed that all 4 LED's were on before taking off.

Koelkop Posted at 1-29 11:21
I will not trust that battery at all. Its brain went coo coo. At the start the cell voltages suddenly dropped to 3.5v, that is already at the 20% level more or less.

Was the battery fully charged? Or why was it at less than 90% at startup?

No it did not give me any low temp/cold battery warning.

Yeah, I could not control it once the forced landing was initiated. The screen showed something like "Forced landing" and there was a red X (like "close"/"cancel" symbol) on the screen but I did not dare to touch anything once it was initiated. Pressing that, would I then have been able to cancel the landing? And would the AC just hover at current altitude then?

Hi there, thank you for reaching out and we're sorry to hear about the trouble, with regards to that Kind send me some direct PM providing the Serial number of the Aircraft and Battery and make sure you already sync the flight records as well for us to check what can be the possible workaround we can provide. Thank you for your consideration.

Mulle Posted at 1-29 11:43
No it did not give me any low temp/cold battery warning.

Yeah, I could not control it once the forced landing was initiated. The screen showed something like "Forced landing" and there was a red X (like "close"/"cancel" symbol) on the screen but I did not dare to touch anything once it was initiated. Pressing that, would I then have been able to cancel the landing? And would the AC just hover at current altitude then?

Hi Mulle,

Another bad luck with your MA.

A forced landing (due to critical battery level) cannot be cancelled.

But throttle up will stop the descent, if the batt has enough power left.
Not sure if, when the battery is too cold, if stopping the descent is possible.

Cell #2 is the 'error' (green line)

Start values looks oke, but Voltage is dropping to low values soon.
Comparison My-Yours MA

My > 87% = 11,6 Volts, 82% batt > 11.5 Volts.
Yours > 87% = 12.0 Volts, 82% batt > 8.7 Volts.

So all cells are loosing voltage way to soon, due to cold temps or just a bad battery.
As it was the second batt, did you keep the batt warm before installing it in your MA?

In the log is a batt error : First "BattTempVoltageLow" at 83% with 9.7 volts.

My advice is always load battery to 100%, even after few days not in use and leds indicating 3 or 4 leds.
So fly away with 100%, sometimes (if something unexpected is happening) you need all the power to bring the drone back home.
cheers
JJB

DJI Gamora Posted at 1-29 12:05
Hi there, thank you for reaching out and we're sorry to hear about the trouble, with regards to that Kind send me some direct PM providing the Serial number of the Aircraft and Battery and make sure you already sync the flight records as well for us to check what can be the possible workaround we can provide. Thank you for your consideration.

Sure, you'll have a PM in a minute.

JJB* Posted at 1-29 12:15
Hi Mulle,

Another bad luck with your MA.

Thanks for the analysis!

That green line is not nice. The battery had been in the trunk of the car for maybe 30 minutes before flying so it might have been a bit cold. But would that be causing such sudden drop in voltage? I find it strange that it indicates 82 % left although the voltage is really bad.

Not sure if I tried to to throttle up during the forced landing, was pretty busy running through the field to make sure I saw where it landed. The woman staying in that house was not too happy and told me to take my toys elsewhere...

Mulle Posted at 1-29 12:34
Sure, you'll have a PM in a minute.

Thank you appreciated!

Mulle Posted at 1-29 12:50
Thanks for the analysis!

That green line is not nice. The battery had been in the trunk of the car for maybe 30 minutes before flying so it might have been a bit cold. But would that be causing such sudden drop in voltage? I find it strange that it indicates 82 % left although the voltage is really bad.

Yep, strange indeed. Not always are the % batt level in sync with the voltage values.
I have seen this more on this forum.

Don`t know why, read somwehwere that after while its better to install a (low) batt in AC, switch in ON, OFF again and than load batt with normal charger to 100%, this way values % - Volts are in sync.

cheers
JJB

Sorry to hear about all the mishaps.
Had a similar error with the battery myself.
I was given this advise ." Don't fly with this battery"
My  Battery error comes and goes. So I decided to play it safe and got a new Battery.

Here is my post. Battery error

hmm... The cell deviation is a bit high in my opinion so the battery might just be too old, too cold or has other issues. As far as I know, you cannot stop a forced landing the computer I believe takes over to preserve the aircraft, though you can steer it a little I believe. As far as pre flight checks go, I would recommend letting it hover for a few minutes to let the battery heat up given that it was 0°C before going away from you.  

Dirty Bird Posted at 1-29 15:13
You can always maintain (or increase) altitude by applying the throttle, even during critical battery.    You can in fact keep the bird aloft until the pack shuts itself down.  You have full directional control as well.  Just don't panic, keep your wits, & you'll the opportunity to bring you bird down safely.

One of the sadest videos I watched was a guy flying his Spark back from a long flight out over the ocean.  Just a few hundred feet from shore it hit 10% & went into Auto-land mode.  The poor bloke just sat there & watched his bird slowly settle into the abyss, not realizing he could have easily flown her home.

yep, i did try did once....keeping the bird in flight hovering until 0% battery.

Why, just learning to see what happend in all situations.
Same with the RTH procedures ; just try them all out (normal, low batt, crit bat ) with different distances from home.
Try out disconnect (simply switch off your RC) and see how the drone reacts, how it is re-tracing route etc for a MA.

If only alll beginners would read all relevant items on this forum less mishaps would happen!
Read and understand the manual, try things out etc before flying 'difficult' flights, or above water in a second flight!



cheers
JJB

Dirty Bird Posted at 1-29 15:13
You can always maintain (or increase) altitude by applying the throttle, even during critical battery.    You can in fact keep the bird aloft until the pack shuts itself down.  You have full directional control as well.  Just don't panic, keep your wits, & you'll have the opportunity to bring you bird down safely.

One of the sadest videos I ever watched was a guy flying his Spark back from a long flight out over the ocean.  Just a few hundred feet from shore it hit 10% & went into Auto-land mode.  The poor bloke just sat there & watched his bird slowly settle into the abyss, not realizing he could have easily flown her the short distance remaining to home.

Oh really, that's good to know. So basically I could have closed the "forced landing" message on the screen and then to some extent regain control? But I guess it will still be in "forced landing mode" so what if I just let go of the sticks, will it then continue its forced landing again? What I mean is that I have to continuously throttle up in order for it not to land?

Mulle Posted at 1-30 11:19
Oh really, that's good to know. So basically I could have closed the "forced landing" message on the screen and then to some extent regain control? But I guess it will still be in "forced landing mode" so what if I just let go of the sticks, will it then continue its forced landing again? What I mean is that I have to continuously throttle up in order for it not to land?

I dont believe flights purposefully engaging casualty procedure is prudent.
And i posted two biggy paranoia(s):
1)  flight time insufficiency by designed energies reposit and consumption of said energies
2) link safeguarding from obstructs all (emi jamming, infrastruct, etc.)

Of course this resolves significantly flyaways and collides.

Mulle Posted at 1-30 11:19
Oh really, that's good to know. So basically I could have closed the "forced landing" message on the screen and then to some extent regain control? But I guess it will still be in "forced landing mode" so what if I just let go of the sticks, will it then continue its forced landing again? What I mean is that I have to continuously throttle up in order for it not to land?

no need to close any message on the screen, just use the sticks to control the craft.
And yes, keep it up to keep height or even increase height. If you let go all the sticks, craft will continue his autolanding.
Just give it a try, hover at few meters height close at your homepoint, wait until 10% batt reached and see what is happening, control the sticks and be amazed!

cheers
JJB

Regarding the secondhand purchasing, was it proofed by some kind of dji comprehensive procedure of satisfactory operational  testing?

Or such procedure of full operability is dji provided nonexistent?

used battery, could been abused heavily such as agressive discharging and/or improper stored for much of its life, you dont know how it was treated and probably unbalanced and failed...    i do not think it is the cold, i flown in super cold conditions.. negatives..  -20C in fact.. and my battery didn't act this way.  this symptom of cell failure/severe cell imbalance.


really only thing i have for you to try is dull discharging.  basically charge battery up till full, then turn it on in the drone, let it sit doing nothing until it dies, pull it out and charge back up, and repeat a few times.. this sometimes forces the cells to rebalance and zero themselves out basically... doesn't always work really depends how bad that broken cell is..if its too far gone this wont fix it, but it is possible it could rebound if properly rebalanced with other cells.

Could any of these XX% to 0% battery drops be connected to the smart battery self-discharging function?

Maybe a matter of bad timing?

Bluehook Posted at 1-31 17:12
Could any of these XX% to 0% battery drops be connected to the smart battery self-discharging function?

Maybe a matter of bad timing?

yep definitely could be.. happened a lot before but less common today.    basically what used to happen was the battery drop into self discharge mode and then fall asleep and so when plugged it in it thought the battery was say 85% when it was really 30% then it would give you a real wake up call when all your juice dropped out of it..  

good news is it appears less common of an issue, DJI has scripted some stuff in to protect aginst this mroe and more, however i do not know if the mavic air batteries are able to run all the protections n software, so definatly possible.  ... maybe ill leave a battery out for a couple weeks at 90% so not full and doesnt hurt itself... and see if it does it to me..

Update:Since the forced landing incident I have update firmware in AC and RC. Have discharged the bad battery by letting it sit in the powered on AC, and then fully recharged it. Today I took it for a flight with that same battery:

https://www.phantomhelp.com/LogViewer/UMNZRFVKPXHOQ5GBBU43/
continued here https://www.phantomhelp.com/LogViewer/SPQXPIYJN0JNO7I99X71/

Looks fine I think. Although after the minor crash during the forced landing I have had to calibrate the compass each time I restart the AC and I am also getting some errors on the obstacle avoidance during flight.

Mulle Posted at 2-1 08:35
Update:Since the forced landing incident I have update firmware in AC and RC. Have discharged the bad battery by letting it sit in the powered on AC, and then fully recharged it. Today I took it for a flight with that same battery:

https://www.phantomhelp.com/LogViewer/UMNZRFVKPXHOQ5GBBU43/

Hi Mulle,

2 flights with not a single error!

First flight batt max cell deviation 108 mVolts, cell# 2 little lower.
Keep checking this next flights

happy many landings,
cheers
JJB