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Battery went from 100% to critically low after few seconds of flying.

Mycamblur

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This happened to me today, for the first time with my Mavic Pro. A new non-DJI battery - the flight was normal until shortly into the return leg of the flight, at which point the drone was around 1.8km away and had 70% battery on the screen. This suddenly dropped to 8%, putting the drone into a forced landing that I could do nothing about. It came down in someone's garden, luckily not on a roof top or road, and using the app map, I was able to find it. A lucky escape.

It was a cold day 3C, but I've flown long flights in snowy mountains before, with no issues, with air temperature below zero. I think this was due to it being a non DJI battery.
 
This happened to me today, for the first time with my Mavic Pro. A new non-DJI battery - the flight was normal until shortly into the return leg of the flight, at which point the drone was around 1.8km away and had 70% battery on the screen. This suddenly dropped to 8%, putting the drone into a forced landing that I could do nothing about. It came down in someone's garden, luckily not on a roof top or road, and using the app map, I was able to find it. A lucky escape.

It was a cold day 3C, but I've flown long flights in snowy mountains before, with no issues, with air temperature below zero. I think this was due to it being a non DJI battery.
Was the battery freshly charged before the flight?
 
Yes, recharged a couple of days before. It had been used for a flight 10 days earlier, but other than that, was new.
If you post your recorded flight data, that might help solve the mystery.

There are a couple of options ...

1. Go to DJI Flight Log Viewer | Phantom Help
Follow the instructions there to upload your flight record from your phone or tablet.
That will give you a detailed report on the flight data.
Come back and post a link to the report it provides and someone might be able to analyse it and give you an understanding of the cause of the incident.
or
2. Just post the .txt file here
or
3. If you use Airdata, you can view the flight data on Airdata and post a link for the Airdata report
 
Thanks @Meta4 . Done that. Link here. DJI Flight Log Viewer - PhantomHelp.com

You'll see that all was normal until 7 minutes 2 seconds, when the battery went from 77% to 8% within the space of 5 seconds. 1.8 km from base and over a residential area, so not the best. Luckily it landed safely, and at a place that I could easily access - all just by chance I guess. Could have so easily ended up on a busy road or a roof top.

So it was a new battery (only it's second use), was fully charged a couple of days before, and showing 100% on take off. It was a non DJI battery though (suitable for Mavic Pro said the ad). It was a cold day - air temp 3C at ground level. Battery had been in the house except for the 15 minute drive to the fly site, so I did not expect battery temp to be an issue, though in the logs I see there was a battery under 15C warning.

Nevertheless, it should not have failed so catastrophically.
 
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In this case the cells them self didn't fail, they all 3 held up the voltages good without any noticeable deviations... & the BMS chip also initially calculated the percentage correctly.

But 422,3sec into the flight, there in RTH... the BMS percentage calculation went haywire, quickly ramping down to 0%. This made the indicated battery percentage breach the "critical low voltage level" threshold at 431,7sec (was 15%)... which made the drone to go into autolanding.

So this was most probably a BMS failure... not anything related to the actual voltage the battery could put out.

(Click on the chart to make it larger, graph explanations in the legend below & values from marked 431,7sec)
1705578178101.png
 
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Thanks @Meta4 . Done that. Link here. DJI Flight Log Viewer - PhantomHelp.com

You'll see that all was normal until 7 minutes 2 seconds, when the battery went from 77% to 8% within the space of 5 seconds. 1.8 km from base and over a residential area, so not the best. Luckily it landed safely, and at a place that I could easily access - all just by chance I guess. Could have so easily ended up on a busy road or a roof top.

So it was a new battery (only it's second use), was fully charged a couple of days before, and showing 100% on take off. It was a non DJI battery though (suitable for Mavic Pro said the ad). It was a cold day - air temp 3C at ground level. Battery had been in the house except for the 15 minute drive to the fly site, so I did not expect battery temp to be an issue, though in the logs I see there was a battery under 15C warning.

Nevertheless, it should not have failed so catastrophically.
Comparing the battery % indication with the cell voltages, something doesn't add up.
Everything looks normal with the cell voltages and charge level both steadily and slowly decreasing until 7:05.6, when the charge level drops from 47% to 38%.
But there is no corresponding drop in the cell voltages which continue to fall gradually (which is normal).
The Charge level continues to fall very quickly, jumping from38-30-24-19-15-12-10 etc, but the cell voltages appear normal.
When the Propulsion output has been limited to ensure battery health warning shows at 7:16.7, the charge level shows 6% but cell voltages are showing approx 3.8 volts - well above critical low voltage level.

It's hard to see what is causing the the mismatch between charge level and cell voltages.

Unfortunately there is no data for battery temperature, so that can't be investigated.
It looks like a technical problem with the circuitry inside the battery, rather than a problem with the battery itself?
 
...Unfortunately there is no data for battery temperature, so that can't be investigated.
The battery temp is kind of secondary... anything out of the ordinary (colder or warmer) will converge to a higher internal resistance which will cause voltage drops during amp draw... but here the cell voltages is normal, so likely nothing odd regarding the temps.
 
Thanks so much for your input guys. In any case, I don't feel safe using this battery, so I am returning it whilst I still can. The battery management system chip failure that you refer to, I am not sure where this is. Is it in the battery or in the drone? If it's in the battery then I think I should indeed return it. If it's in the drone I don't know what I can do.
 
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Why take the risk of using a non DJI battery? Is it not a warranty violation?
Well the drone is well out of warranty now anyway, but yes, lesson learned. Got it as it was new, and the only DJI ones I could find were second hand, so I figured a new one would be better, but not so.
 
well above critical low voltage level.
Would that explain how this MP was able to land with 0% showing in the graph for some duration of time?
Certainly had a rather long travel distance to get to ground level. (negative altitude numbers)
 
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Would that explain how this MP was able to land with 0% showing in the graph for some duration of time?
Certainly had a rather long travel distance to get to ground level. (negative altitude numbers)
In general & with a battery on true 0%...

A DJI battery have a cell voltage of close to 3,5V when the BMS says 0%... that is pretty far from being critical for real. The danger here was that the OP took of already up on height which tricks the BMS regarding how high the drone actually is above solid ground (the critical low voltage auto landing percentage threshold is height dependent).

But from 3,5V/cell the voltage drops much faster than before... so yeah, a landing from + 164ft down to -305ft instead of 0ft can mean freefall in the end.
 
Return it AND return any other non-DJI batteries, without question. Non-DJI batteries will NEVER have the kind of circuitry that is required for them to truly be safe for use in the manner a DJI battery will and you have no way to know the quality of any of them. They are, IM not so H Opinion...a truly bad investment.
 
Return it AND return any other non-DJI batteries, without question. Non-DJI batteries will NEVER have the kind of circuitry that is required for them to truly be safe for use in the manner a DJI battery will and you have no way to know the quality of any of them. They are, IM not so H Opinion...a truly bad investment.
But it's difficult or impossible to find genuine DJI batteries for older drones.
 
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