How to Analyze Battery Health / Flight Reader

[smbishop]

I use Flight Reader to log and track my flights. What are some ways to check over all battery health other than number of times charged?

 

[mobilehomer]

Airdata account. Lots of battery info for each flight.

 

[smbishop]

Airdata account. Lots of battery info for each flight.

Thanks, I have an Airdata 360 Lite, not much battery information at that level.

 

[mobilehomer]

Thanks, I have an Airdata 360 Lite, not much battery information at that level.

I have the free account. There is TONS of battery info. Look at all the different tabs under the Power heading.

 

[RadioFlyerMan]

I use Flight Reader to log and track my flights. What are some ways to check over all battery health other than number of times charged?

I track the battery net capacity as a function of total watt-hrs of usage. The values are retrieved and summarized using data from the flight records. When it drops below 80%, I stop using the battery for flight.
Here’s an example graph of one of my M2P batteries…

 

[msinger]

I track the battery net capacity as a function of total watt-hrs of usage

Can you share your calculation? Any need to consider the efficiency of each battery cell individually?

When it drops below 80%, I stop using the battery for flight

Why did you decide to choose 80%?

 

[RadioFlyerMan]

Can you share your calculation? Any need to consider the efficiency of each battery cell individually?


Why did you decide to choose 80%?

Yes, but I'll have to get back to you later to provide a comprehensive response. Right now, I need to run a Waypoint mission before the weather goes bad.

 

[RadioFlyerMan]

Can you share your calculation? Any need to consider the efficiency of each battery cell individually?


Why did you decide to choose 80%?

Some background:

I download and store all of the flight records for each drone. They are processed and stored in an Excel spread sheet using routines I developed in VBA. Once the TXT file is retrieved via iTunes, the processing of a flight is totally automatic. Developing my own tracking software is another enjoyable element of this hobby. It keeps my aging brain healthy!

I use this flight data to display flight statistics, flight paths and modes, camera paths and photographic modes, battery power and cell voltage deviations, and various custom data events in Google Earth Pro using an automatically generated KML. Here’s an example of flystates…


Tracking Battery Health:

Another key use of the data is to track the health or condition of each battery. With all flight records available, I choose not to use the number of charge cycles as that would require an additional step of data retrieval and entry.

For tracking battery health, I graph the current full capacity of each battery as a function of total watt-hours of energy used for that battery. Since the total watt-hrs for a battery is an accumulated value over time, it requires that all flight records be processed to acquire a complete history of use. The flight record parameters for this calculation include:

Current maximum capacity as a percentage of design:
- Center_Battery.fullCapacity [mAh] (maximum recorded )
- The theoretical design capacity of the battery (DJI’s value)

Total energy used during the flight:
- Center_Battery.CurrentPV [V]
- Center_Battery.Current [A]

I derive the watts-hr for each flight by summing the Volts x Amps for each 10th of a second, then converting them to watt-hrs over the duration of the flight…. Sum(V x A) /10/60/60. It’s really a weighed average of the power for each accumulated second of flight. This approach is not perfect, but it’s good enough to view the degradation of the battery as a function of its actual use.

For purposes of graphing the data, the independent variable, energy usage, is tabulated in increments of 45 watt-hrs with the associated battery capacity values calculated as a weighted average. The 45 watt-hrs is arbitrary and was chosen to simply “smooth out” the graph. The scale on the left of the graph is for displaying maximum battery temperature (turned off in this example). I track maximum battery temperature with energy usage to see if a high temperature exposure impacts the capacity of the battery. I have not seen anything out of ordinary, however, I don't live in Florida!


Here’s an interesting development… I purchased new batteries from DJI for my M2P. The first flight’s were disappointing as they were displaying less than design capacity. However, as I used the batteries, the capacity increased. I did not expect that.


I also summarize the voltage deviations for each cell. As the battery degrades with use, the frequency and magnitude will increase. My quantized values for voltage deviations are 0 to .05, .05 to .075, .075 to .100, .10 to .15 and .15 to .20 and greater.




FYI... an issue with all downloaded flight TXT files is that there will be missing 10 hertz records for a variety of reasons. I have also seen on a rare occasion when the time stamp from one record to the next is reversed. To remedy this, my programming performs a determination of the missing records and fills them in based on the assumption that most flight parameters will not change much over the course of 1/10 of a second. This approach provides better data for those parameters that are totaled or averaged over the entire flight.

As to the issue of when to stop using the battery, it is very subjective and arbitrary. It’s a matter of trust. When I see the battery capacity drop below 80% of design, combined with a substantial shift of cell voltage deviations toward the higher ranges with high frequency, I get nervous. In practice, I have stopped using only one battery that came with my original MPP back in 2018. It displayed a rather large drop in capacity, at one point early in its life, followed by ever increasing voltage deviations over the last couple of years. I use this battery only for powering my “nuclear powered”, 4 Hawks antenna.

One other comment. When I first started flying in the fall of 2018, I was not aware of how to properly treat LiPo batteries. That’s probably why one of my original MPP batteries went bad. Today, if I’m just joy-riding around my neighborhood, I land at 60%. If a battery sits on the shelf for more than 30 days, I’ll charge and fly it back down to 60%. If I’m filming for a video, I always try to land no less than 30%, most of the time. So far, no bulging batteries!

I hope some of this makes sense.