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Battery lifetime and Dangers
1469 15 2020-2-20
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nullx8
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quick question, at how many cycles is a battery considered "unreliable" ?

also if there is optical change (getting bigger) visible, at what level is it unsafe to use it ?

one of my batteries has 153 cycles and it does start to get "bigger"  i can fly 22-25 minutes with no problem, so there is no loss of capacity yet.
IMG_4571.JPG

whats the rule of thumb ?

2020-2-20
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hallmark007
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First I don’t think there is any real research on this, but I can tell you that it seems like there might have been a bad batch of batteries with similar problems to yours, and for those who contacted dji got battery replaced.
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Mell
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That can be dangerous. I wouldn't keep such batteries at home.
After i saw this video i pay much more attention to LiPo batteris. Current baqttery,s are smart ones but still never know what can happent.
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nullx8
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hallmark007 Posted at 2-20 05:21
First I don’t think there is any real research on this, but I can tell you that it seems like there might have been a bad batch of batteries with similar problems to yours, and for those who contacted dji got battery replaced.

yeah they are out of warranty already ...
i just had a chat with Customer support.
6 Months and 200 cycles is the warranty time... guess its time to get some new ones.
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DJI Gamora
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Hi, thank you for reaching out and we're sorry for the inconvenience caused. As we review the image that you had sent, it shows that the battery is no longer safe to use since it shows that the battery got swollen and we highly recommend you to use a new one for your own safety purposes. Also, dispose the swollen batteries correctly, You may refer to the link below for your future reference. Thank you for your understanding and support!  

https://dl.djicdn.com/downloads/ ... tery+Safety+Guides+(EN).pdf
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FatherXmas
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All four of my Mavic Air batteries swelled up like that at the same time. They were out of warranty so I bought two new ones, at $70 a pop, two was all I could afford right now.
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nullx8
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i found a local guy that replaces the cells, i made a test order today .. i sent him my old battery (that solves the recycling problem) and same time he send me a repaired one.
30$ a pop ... pretty good deal.

lets just hope the mavic is not falling out of the sky some day
2020-2-21
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nullx8
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FatherXmas Posted at 2-20 09:32
All four of my Mavic Air batteries swelled up like that at the same time. They were out of warranty so I bought two new ones, at $70 a pop, two was all I could afford right now.

how many cycles did your's have when they start ?
mine had 115 .. strangely i have 2 more with 158 and 192 cycles and they are just fine.
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bjr981s
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nullx8 Posted at 2-21 02:33
how many cycles did your's have when they start ?
mine had 115 .. strangely i have 2 more with 158 and 192 cycles and they are just fine.

Battery swelling occurs when you over discharge a battery.

You are flying them to max flight time. This will limit the lifetime cycles to just over 100.

If you fly to 50% flight time you will get over 500 cycles.

Basically every time you discharge to a low level (Below3.7V per cell) you are reducing the cycle life.

Cheers
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Mell
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bjr981s Posted at 2-21 03:57
Battery swelling occurs when you over discharge a battery.

You are flying them to max flight time. This will limit the lifetime cycles to just over 100.

When is good to land? When 10-20% battery left?
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bjr981s
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Mell Posted at 2-21 04:11
When is good to land? When 10-20% battery left?

You need to work that out yourself.

It's a tradeoff of flight time vs battery longevity.

Personally I don't go below 40%

Here is something you need to be aware of.

The DJI smart batteries are not Smart in that they display the remaining voltage.
They are Smart Watt meters. They measure the power that his been injected into the battery.
The down side of this is that as the battery ages you put more in than you can take out.
So DJI attempts to remedy this by asking you to fully discharge the battery and immediately charge again so that the smart "Meter" can get calibrated as the battery ages. But this in itself will shorten the battery life.

But if you don't do this the battery meter lies. You will hear stories of people that had 40% or more battery life left then all of a sudden it goes down rapidly to 0.

I suggest that you keep an eye on the actual cell voltages at different battery indication, levels and mark the percentage left warning to where the cells show 3.7V. That way you will have a safe operation.

Cheers

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nullx8
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i never really flew them empty .. iam way too scared that i can't make it back and lose the Mavic in the process, so usually its always arround 30ish %
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nullx8
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bjr981s Posted at 2-21 04:36
You need to work that out yourself.

It's a tradeoff of flight time vs battery longevity.

very insightful your post,

quick thing: is it better to "always" charge the batteries generally (using the DJI chargepad ?
because this is what i did with mine.

about the quick drop to 0% .. yes i can confirm that (not with DJI batteries but with others like my iPhone) ;)

what i find strange that there is literally no loss of capacity with the swollen battery i have, its "just bigger" i can fly it just the same time, i usually return at 50%ish and iam not really the type of person that fly 5km away so the return flight is usually takes me just moments with plenty of battery left.
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Kodak45
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While swollen batteries still support flight- they are more likely to force the latches loose.  Several instances of battery loss in flight discussed on MavicPilots
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Matthew Dobrski
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Kodak45 Posted at 2-21 11:07
While swollen batteries still support flight- they are more likely to force the latches loose.  Several instances of battery loss in flight discussed on MavicPilots

Although most of the above said is true, this is probably the most relevant reason to replace swollen battery ...
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bjr981s
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nullx8 Posted at 2-21 08:01
very insightful your post,

quick thing: is it better to "always" charge the batteries generally (using the DJI chargepad ?

The reason that the battery "swells" is because there has been a chemical breakdown in the cells and it has given off a gas. The gas is highly flammable. So there is a danger.

That also means that the cell is not 100%. Now the DJI sensor system in the battery that provides the battery cell voltage will warn you if one of the cells is damaged enough that it can't balance the cells.

So if you don't get a battery damaged warning it will still work OK.

Just be warned that it will continue to deteriorate and swell further.

There is a risk that the damaged cell may just give way in flight but its pretty small given the low C rating these batteries have and the small current draw.

Swelling batteries is a problem we face continually in flying Ducted Fan jets, as the current draw is so high

If you remember the C rating factor being A = CxAH so a 50 C 1,000mah battery will max out at 50Amps max draw.

But if its only half charged thats 25A etc. You can get into the voltage brownout situation if you put a call on the battery for a high current draw when the battry is low on charge. This results in a brownout that can effect the flight controller.

The best bet is to cycle the batteries as per the DJI instructions to calibrate the meter. And keep plenty of reserve battery at hand.

Flying Helis and Ducted fan or prop fixed wing we normally use a seperate battery for the receiver and Flight controller if fitted. If the main battery dies we can glide or autorotate to a soft landing. A Drone glides like a brick. So good battery management procedure is a must.  
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