Mavic Air - Battery life expectancy and when to discard them for a new battery

[Andy England]

Hi Guys
I had a flight today which almost resulted in a loss due to rapid and unexpected battery power drop.
I looked at the flight data in Airdata UAV and see the battery has been recharged 33 times...
It also showed deviations in cell 3 although all three dials are still in the green zone.
What conditions or metrics should be used to recognise the battery has reached the end of its useful lifespan and you risk having a catastrophic battery failure during a flight?

 

[slup]

Hi Guys
I had a flight today which almost resulted in a loss due to rapid and unexpected battery power drop.
I looked at the flight data in Airdata UAV and see the battery has been recharged 33 times...
It also showed deviations in cell 3 although all three dials are still in the green zone.
What conditions or metrics should be used to recognise the battery has reached the end of its useful lifespan and you risk having a catastrophic battery failure during a flight?

View attachment 97451

Below is from one of my post over at the DJI forum ... think it can shed some light on your question.

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As I see it it's mainly 2 thing's that keep our drones airborne ... props & batteries, if any of them fail the aircraft goes down as a rock.

When it comes to the props I think all understand that nicks, bends, hits & general abuse risk the coming flights ... it's pretty common that pilots add an visual check both of the props them selves but also regarding the attachments.

But batteries ... what about "nicks, bends, hits & general abuse" on them?

Yeah ... can be hard to check off visually, some leave them in the charger so they always are 100%, others just store them full to be ready for the next flight opportunity. Some fly them really low then leave them waiting weeks for the next flight session. Or perhaps store them in a hot car, maybe charge them directly after a flight still hot? All this is major battery abuse not seen outside.

It's so many ways people abuse their batteries ... none of the ways will show any visual damage. If they take charge to 100% all seems fine ... or?

Aside the most obvious visual damage of a battery ... swelling, it's hard to judge when it's time to take a battery of flight duty & just use it for ground duty like settings & offloading pics & movies.

But it exist one way ... this way consists of monitoring the battery performance & cell deviation over time ... the trends. The trend is important as all batteries degrade over time & usage ... until the point where some of the cells in the battery suddenly fails & leaves our drone mid air without enough voltage to sustain continues flight.

Airdata.com have this with battery trend followup's pretty good layed out ... of all flight logs you have there you can read off the performance & cell deviations over time, you can monitor the degradation & take it out in time before something happens. (This functionality is unfortunately only included in their payed subscriptions ... but I see it as an insurance well worth the cost)

This is a couple of graphs from there, based on all my hundreds of flights ... one of my best & one of my worst batteries.

The best (from 18 July 2019):

And from the latest flight with it ...

Then the worst (from 15 Jan 2019):

And from the latest flight with it ...

And then if we compere the above individual flight graphs with a battery with a failed cell below (no trend, only what happened during one flight)
This didn't happen suddenly ... this is the final stage of a longer period of degradation, if this battery had been followed it should have been grounded much earlier.

A LiPo cell have a max voltage of 4,2V & below 2,7-3,0V it starts to get permanent damage ... 50% battery is approx 3,7V
So this battery is now permanently & severely damaged as cell 3 were discharged well below the minimum cell voltage ... it fell all the way down to just below 2,3v. Dji Drones will start autoland when the cell voltage goes below 3,0V.

This battery were totally messed up already several flights before this, in a sense a time bomb ... very much alike a brutally abused prop with cracks & large chunks broken off.