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What cell voltage difference is cause for concern?
1123 4 2019-1-30
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szh
lvl.4
Flight distance : 252139 ft
Germany
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One of my Mavic Pro batteries just failed. The controller displays "battery error" and the voltage on one of the three cells is 0.15 V lower than the others.

I assumed that this happened because I have not used the drone for quite a while (moved to a country with strict regulations, and fewer opportunities to fly), or because or the very first time I got sloppy and did not immediately recharge the battery after use for almost a month.  Either way, after an internet search it seems that the battery is not salvageable (a full discharge then recharge does not help). My question is about something else.

If I look at old logs, I can see that a voltage difference was always present. My oldest log is from September 2017:

Screenshot 2019-01-30 14.17.05.png

Perhaps this failure was going to occur either way, even if I am more careful with charging (not that I'll ever neglect to do that again...)

My question is: How great a voltage deviation should be cause for concern? The highest deviation on my other battery is always smaller than 0.02 V.  If I get a new battery, and see that it has a deviation of 0.05 V out of the box, should I send it back? Would that indicate that the battery is bound to fail prematurely?
2019-1-30
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HereForTheBeer
Captain
Flight distance : 5381368 ft
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United States
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0.1 volts is the rule of thumb.  Anymore than 0.10 volts and I would say it’s a cause for concern. Deviating typically increases with age and cycle count of the cells as internal resistance increases and excepted wear and tear occurs.  If 0.10 volts deviating happens in flight it doesn’t mean your aircraft is coming down, but if your aware of it happening regularly,  you should mark that battery that way you have a visual cue of which battery is wearing more.   My Mavic Pro didn’t start having cell deviation as large as 0.10 volts in flight until around 130 charge cycles but I was more abusive than most people, using sport mode a lot, flighting to absolute limits, improper storage conditions (but not too severe) I basically treated it like farm equipment and it held up, but I also flew every day or every few days so it rarely sat around which apparently is how a lot of failures happen is people toss them in drawer at 100% for a month or two and come back to problems.

Your cells are fairly healthy if they only deviating 0.02 - 0.06 volts, but if you are seeing 0.15V deviation then yea, sorry.. that’s beyond recovery for 99.9% of people.  as for how to determine if battery is going to age rapidly, few things.  Regular deviations of 0.10V or greater during flight, large voltage sag during flights like if it’s 12V and then switch to sport mode and blast off for a second and drops to 10V that’s not great means battery can’t keep up with demand,  and Finally, while flying around gently if your pack gets very hot, like 60C or over that means lot of resistance building up because resistance creates heat when demand is high..
Personally that last point is why I am worried about the Mavic Air aging rapidly, all my packs get much hotter than I think they should,  it was 0F out and my packs were probably 70F and very little wind did a flight and my mavic air’s packs got up to 50C.. now I didn’t land at 30% I landed near 10%  but I don’t that same thing when I had Mavic Pro. And when I landed it was 30C or 35C and it was a slightly warmer day.

2019-1-30
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szh
lvl.4
Flight distance : 252139 ft
Germany
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HereForTheBeer Posted at 1-30 08:07
0.1 volts is the rule of thumb.  Anymore than 0.10 volts and I would say it’s a cause for concern. Deviating typically increases with age and cycle count of the cells as internal resistance increases and excepted wear and tear occurs.  If 0.10 volts deviating happens in flight it doesn’t mean your aircraft is coming down, but if your aware of it happening regularly,  you should mark that battery that way you have a visual cue of which battery is wearing more.   My Mavic Pro didn’t start having cell deviation as large as 0.10 volts in flight until around 130 charge cycles but I was more abusive than most people, using sport mode a lot, flighting to absolute limits, improper storage conditions (but not too severe) I basically treated it like farm equipment and it held up, but I also flew every day or every few days so it rarely sat around which apparently is how a lot of failures happen is people toss them in drawer at 100% for a month or two and come back to problems.

Your cells are fairly healthy if they only deviating 0.02 - 0.06 volts, but if you are seeing 0.15V deviation then yea, sorry.. that’s beyond recovery for 99.9% of people.  as for how to determine if battery is going to age rapidly, few things.  Regular deviations of 0.10V or greater during flight, large voltage sag during flights like if it’s 12V and then switch to sport mode and blast off for a second and drops to 10V that’s not great means battery can’t keep up with demand,  and Finally, while flying around gently if your pack gets very hot, like 60C or over that means lot of resistance building up because resistance creates heat when demand is high..

Thanks for the response.

"0.1 volts is the rule of thumb."

My impression was that this is about the difference beyond which the drone refuses to take off (that's based on other complaints about similar problems on this and other forums).

My question wasn't really about when to stop using the battery. With such a deviation, the device would prevent me from using it anyway.

"Deviating typically increases with age and cycle count of the cells"

What I'd like to know is related exactly to this: what's too much for a new battery?  If a new one has 0.05 already, I guess that means it will fail faster ... I don't know what mine looked like when new, but looking at old logs for the first time I can see that it has 0.05 V deviation already after 10 charge cycles, even though at that time I certainly did not push it hard (have not even tried sport mode yet, and I was generally careful with usage, maintenance and storage).
2019-1-30
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szh
lvl.4
Flight distance : 252139 ft
Germany
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Actually, I *just* found the logs from the very first flights, and it seems that the deviation was only 0.01 at that time, gradually increasing over time. So I could not have predicted the problem by looking at the brand new battery anyway.
2019-1-30
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Koelkop
Second Officer
Flight distance : 22814806 ft
South Africa
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My experience so far is that these batteries like to be cycled. Its usually batteries thats been stored for a long time that the cells start to deviate.

I bought my mpp 11 months ago with 3 batteries, all 3 has over 200 cycles and at 100% takeoff the cells differ by about 0.03v, at 50% its down to between 0.001/0.004v difference. And they have been down to 0% and regularly below 20%. I am very happy so far
2019-1-30
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