cjr888
 lvl.4
Flight distance : 3686988 ft
Czechia
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I was wondering about condition of my Air's batteries, especially whether it's safe to still use them or not so I did my homework and checked last 50 flight logs.
As mentioned in title, I've been using these batteries for a year now. They're made in 8/2018, according to SN checker.
Battery #1 has 77 charge cycles
Battery #2 has 76 charge cycles
Battery #3 has 74 charge cycles
All three batteries were used according to DJI battery usage guide - never discharged below 20% of indicated capacity, never flown when colder than 25°C and always charged after they cooled down completely after flight. Stored at 60% when not in use for more than few days and charged prior the flight.
About what I've been analyzing and why.
Every intelligent flight battery inside Mavic Air sustains from 3 battery cells with certain voltage. As the battery gets worn out, some of its cells might become unstable and starts dropping its voltage while others are not. This makes voltage values between cells unbalanced. This voltage difference is called a cell deviation. It may happen more frequently when battery is cold or in heavy use (Sport mode flying is a good example) and when battery is low (or more of those things combined). At some point the voltage deviation becomes so serious, that it can cause battery voltage drop so significantly to make it insufficient to keep an aircraft motors running causing it to crash. Some may experienced this as the instant percentage drop from like 70% to 0% followed by aircraft falling from the sky or emergency landing.
Minor voltage deviations between battery cells are pretty much normal and it happens all the time even on pretty much brand new batteries. Cells on every battery usually differ by 0.01-0.03 V and it usually doesn't mean anything.
But things can get worse pretty quickly when batteries are faulty or when they aren't treated well.
Major voltage deviation is when things get serious. When some cell starts to fall behind the others by more than 0.07 V occasionally for a glimpse of second, it can be a little warning of battery starting to be less reliable and may become unstable or dangerous to use in the future.
When the voltage drops on some cell (or cells) become bigger and starts to exceed 0.1V or lasts longer than a few seconds during flight, it's a real deal and this battery should be watched patiently.
My batteries weren't showing any signs of aging or instability during flight so far, so I've been really curious about what I will be able to find. Only expectable thing is slightly shorter flight time.
On brand new battery, my Air consumed 70-71% of battery capacity to achieve 15 minutes of calm flight without sports mode.
On 77-cycle old battery it's more like 80% to get the same flight time so I have to land at 20% to enjoy 15 minutes flight.
Now to the analysis.
My battery #1 appeared to be in best condition when it comes to cells voltage.
I've analyzed 15 flights on this one and only 3 flights were showing some significant cell deviation isolated on 3rd cell.
During one flight there was a voltage drop of 0.129 V which may sound pretty serious but it lasted for only 0.5 seconds before everything went back to normal and stayed that way until the landing.
Otherwise the battery is performing pretty well in other flights as you can see on graph below.
Cell 3 is a little weaker than the others but it's really nothing serious now.
My battery #3 did pretty much as good as #1. Just some very short deviations happening once during a flight.
Only difference is that voltage of two cells is a bit lower than the last one.
It may look bad but the biggest difference I found was 0,02V and all cells are copying the same discharge curve all the time.
Deviations on this battery are a bit more frequent than #1. We're talking about 29% failrate to be more specific. Not bad, not terrible.
Reason why I skipped the #2 battery is that I kept the best for the end. In fact it's not the best but kinda worst but you know what I mean.
My battery #2 didn't do really bad but significantly worse than the other two.
This battery deviation is strictly localized on 3rd cell and occurs on every second flight (failrate is over 50%). In some cases it happened even multiple times during a single flight with more than 10 seconds duration.
Maybe it doesn't sound very serious but the drone was 950ft above ground and over 5000ft away at the moment. In case of more serious cell dropout, I think I couldn't do pretty much anything to prevent drone from freefall.
I actually expected results like this.
Like I mentioned before - not bad, not terrible.
DJI's Li-HV batteries are designed to sustain over 150 charge cycles but this value is just theoretical and is affected by many factors. Mavic Air batteries are one of most efficient batteries in DJI portfolio when it comes to energy density and efficiency but this is at cost of shorter lifespan.
I don't mean this article as a complaint or anything. I just took my flight data and analyzed my batteries stats to prevent some accident from happening in the future. I guess it's bot a bad idea to check your batteries health from time to time, especially when they're over 60-70 charges old.
I already have two brand new batteries in my drawer ready to be activated, just to be sure. But still it's good to know whether it's safe to use my old ones since I want to prevent my Air from any accident or those new batts would be useless :-)
Thanks for your attention.
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