Crash after battery over charge warning

[mirabolo]

Noticed a doubble flash on the third light on my battery, and according to the manual, it indicates battery overcharge detected.
The light did not falsh anymore the day after, and i put it into my mavic, and checked the battery status in DJI Go 4. All looked normal, no error message or warning, and the battery seemed normal (no over charge, and only a very minor inbalance 4.25; 4.25; 4.24).
So I decided to fly the bird anyway.
Twentysomething minutes into the flight, at 26% battery power remaining, I wanted to land it. Short before i was ready to land, i get a battery error message”Battery error. Land soon. View the checklist after landing”. About one minute later, the battery showed 23% left, the Mavic suddenly turned off and fell from a couple of meters above me from the sky.
I can’t think of any other reason for why the bird just turn off midair than a battery failure.

I do have the flight log on my iPad, but unfortunately, the one on the Mavic is gone (i tried endlessly to connect the bird to my computer, and by the time i managed to do that on another machine, the relevant log was already overwritten).
I dicharged the battery and recharged it, and again get the same battery warning,

Anybody else had any simmilar experiences?

 

[Anthony Viscomi]

For starters I would "retire" that battery and certainly not fly with it. If its still covered under warranty I would contact DJI.

 

[microlinux]

Twentysomething minutes into the flight, at 26% battery power remaining

Did you happen to see what the actual voltage was at that point? The % meter is just an estimate and can be misleading in some situations.

 

[mirabolo]

No, i did not check the voltage towards the end of the flight.
But when i discharged the battery again and watched the battery readings, the battery seemed to discharge evenly and without error message, and the % seemed to make sense.
I should get the battery replaced. The damage to the bird is more my concern.

 

[Cyberpower678]

Go ahead and upload the flight log from the iPad. I want to see what happened. I haven't actually checked how high Mavic batteries charge but it shouldn't really be going above 4.2V, though 4.25V is the absolute limit a lipo should be charged to.

 

[mirabolo]

Yes, will upload it when i am back at a PC. Does not seem to work directly from the iPad.

Thanks for your info on the voltage. I have read different things on that in other threads (e.g. here Fully charged battery voltages),and am not sure what range is fine.

The error message mentioned “View checklist after flight”.
What checklist is that/ where to view it?

 

[Geo]

At the least I'd put the battery in the Mavic , fully charged, and fly the Mavic at 3 ft. Let it run for 25 minutes and see what happens. BTW, have a crash pad beneath it (a couple of bunched up towels or the like) in case it does another turn off for no reason.

 

[Cyberpower678]

Yes, will upload it when i am back at a PC. Does not seem to work directly from the iPad.

Thanks for your info on the voltage. I have read different things on that in other threads (e.g. here Fully charged battery voltages),and am not sure what range is fine.

The error message mentioned “View checklist after flight”.
What checklist is that/ where to view it?

Battery voltages should be between 3.3V - 4.2V to operate and prolong longevity. When storing batteries, they should be charged to 3.8V which keep the cells from degrading rapidly. The absolute lower minimum of a lipo is 3.0V, going below that the cell may actually die. If done correctly, you can revive them without degradation, but that's a slow and tricky process, especially since they rapidly lose balance below those values.

 

[mirabolo]

At the least I'd put the battery in the Mavic , fully charged, and fly the Mavic at 3 ft. Let it run for 25 minutes and see what happens. BTW, have a crash pad beneath it (a couple of bunched up towels or the like) in case it does another turn off for no reason.

yes, i have (kind of) done that: recharged the battery, but it in the Mavic, and started the Mavic and let it run without taking off until the battery was fully drained. no incidence. recharged the battery, and got the over charged warning again at full charge.

 

[mirabolo]

Finally got around to download the log file and have a closer look at it. Indeed the beginning charge was somewhat higher than what I recalled, although the imbalance is still small. At some point, the voltage of one cell drops rapidly. The log shows a battery voltage issue 2 minutes before it crashed. The warning appeared only one minute after that initial record in the log, and just one minute before the crash. not much time to get the drone down safely.

I read others had similar issues, although for them the drone went into autopilot and slowly went down without any user control. This did not happen here. I could fully control it until it suddenly turned off. Luckily it was almost at the end of the flight, but still fell a few meter onto concrete.

Sent in the battery for replacement. Not sure how an overcharge happens, and equally how to prevent it without having to stop charging at 80-90% (i.e. how do I know when the optimal point is to disconnect the battery from the charger - the only indication I have are the four flashing lights on the battery).
Also: what do I do when i notice an overcharge? there does not seem to be a way to save/ recover the battery.

 

[Keule]

Sent in the battery for replacement.

The battery is definitely dead. Cell #3 began to show deviations at 06min 28s.
That cell did not recover while in flight. At the end of your flight at around 21 min 11 secs the voltage of #3 was at 3.3v.
At this point the aircraft should have been already on the ground.
Cell #3 began to lose rapidly voltage until the end of your flight. (i attached a .PDF with details)
The total % shown in GO4 was somehow misleading (23%) and you thought it is in a 'safe' condition.

What charger did you use?

 

[Kilrah]

The overcharge message was likely a consequence of that cell being already dead, not the opposite.

 

[kidroc]

mavic batts are HV Lipos so they will charge to 4.30 to 4.35

 

[mirabolo]

Thanks for the thoughts. Yes, it's a lesson for me not to relay on the overall battery percentage indicator only, but to check the single cell values regularly in flight.

On the battery max voltage per cell - I have read about those values mentioned by kidrok, although cyberpoer678 seems to disagree in his above post. Fact is that I got an overcharge warning, which might be because of cell 3 at 4.36 volt (which is above the value mentioned by kidroc.
I am using the charger that came with the drone.

 

[Gubernator]

How old is the battery? Did you ever report it to DJI?

 

[mirabolo]

At the time of the crash, the battery was just over 4 months old, with somewhere around 40 charching cycles if I remember right. Sent the battery for replacement under warranty, but have not heard back yet.