Battery Stats. SoC and Voltage (FP3 and probably FP4)

Hi

Below I have embedded a couple of graphs made from data I have collected over the last week.

Although the date is for an FP3 battery of 3060mAh is is likely to apply to other capacities.

It is also worth nothing this battery is 2 years and 5 months old.

I hope to get info from Fairphone one how the SoC is obtained, probably Columb Counting, but as I cannot implement that I am using a Circuit Voltage formula. (CV) not (OCV)

Using my formula:
The fist graph shows the initial investigation and use the data supplied by the inbuilt Service tests which can be found by dialling *#*#66#*#* then select
Service tests > Test Single > Battery status check.

There are three bit of information that are used

  • The state of charge (SoC) with shows the current capacity in percentage
  • The current voltage
  • The temperature

It is the relationship between the capacity and voltage that interest me whilst I incorporate the temp as a co-efficient as the temp modifies the batteries voltage and hence capacity.

So I will show the first graph and explain how I created it and significant observations

The second graph is just another example but where I had charged the battery to 95% from 9% to get a fuller range.

I’ll be updating this over the next hour and the second graph for a few days.

Whereas I think the graph is self explanatory, maybe that’s only as I developed it so.

  • The x axis is the chronological order but the time between records has no formula or measurable period, they are just times I chose to collect the data. Some are within a few minutes if I had just done a video call another period between data would be over night.

  • The green bars show the SoC which is on a decline as the battery gets used except for data points 4 to 6 where I charged form around 54% to 80% and later in the graph where I charged form 9% to 90%

  • The blue bars are the voltage times ten so it can be seen on the graph and so will range around 40

  • The blue line is a function of the voltage. It’s obvious from the raw data that the SoC and Voltage cannot be easily compared, but the voltage is the main indicator of how much the battery is charged. I have taken a small account of how the the battery has been resting but have not worked that well into the function.

Some Notes

  • Although not easily read from the graph, the voltage data equates to the nominal voltage on the battery of 3.85V when the battery is around 53% charged ~ Date point 25 when the voltage was 3.853

  • The voltage stayed above 3.7V down to an SoC of 16%

  • Once the SoC dropped to 50% there was an increasing dissociation via my formula between the SoC and the voltage, which I would expect.

This shows the battery is more stable and then probably more efficient between an SoC of 80% and 50%

To test out my formula I am doing a second record from 95% and noting the second graph using the same formula I am able to replicate the SoC as a function of voltage.

This was a backwards effort of creating formula where the SoC would be inline with the voltage, but as noted this only works above 50%

Possible Conclusions

With a voltage below 3.6 there is little capacity
With a voltage around 3.7 around 16%
With a voltage around 3.8 around 44%
With a voltage around 3.9 about 60%
With a voltage around 4.0 about 70%
With a voltage around 4.1 about 80%
With a voltage around 4.2 about 86%

If the BMS (battery management system is properly tuned to charging) there seems to a steady, and hopefully the most benign charging between 40% and 80%.

Given the small amount of data it may well be that the range is 20% to 80%

The taken is that below 20% is a strain on the battery and above 80% may lead to a time issue as the rate slows down to mitigate temperature increase.

Regarding the comment from Maximum charging voltage of FP3 batteries:

The voltage measured as referred to is the charging voltage noted by the in built Service test. However if the phone is taken off charge the reading does not alter to any significance and more than that if the battery is removed from the phone, the voltage on the end - and + pins are slightly higher.

So the 4.4v is not an inaccurate measure of the voltage being supplied and then it can be understood that the charging mechanism does not provide more than 4.4v and when the battery stabilises as a pre determined current, as yet unknown, the battery is deemed ‘full’ and the read-out says 100%.

100% output does not mean the battery is fully charged it means it is charged to the limit the manufactures design.

In the build of a 3000mAh battery the maximum could well be 3300mA or as low as 2700 and in either case it may be limited to 4.4V

Ok a second set of data.

Even though this is a smaller set ~ I will populate it with more over the next day or two or three, one thing is clear.

Once the SoC (State od Charge) goes down to 50% I cannot find or create a function that aligns the SoC with the battery voltage.

This lack of alignment shows that the SoC drops quickly below 50% even though the voltage changes little and without a mathematical argument it appears the the battery becomes stressed at this point. If this is the case then I would argue that 50% is the lowest the battery should get to limit a more rapid degradation.

The argument then can be that keeping the battery between 80% and 50% is optimal, and hence the battery only has a 1000mA capacity with best intent.

I do have and am building another set of data to show the rate of capacity change on charging related to voltage, with temperature to discover if there is any concern about raising the upper threshold to 90%.

Although the data is accurate to the phone

  • The data collection may be a misrepresentation due to the on board battery chip
  • The phone’s interpretation may be poor
  • It could be the 28 month old battery

Hence none of the data is provided to infer or encourage people to change their changing habits, but for those who are interested an example of what can be read via the phoneincre.

Sure my home made function is questionable, and if someone can find a better one I will be interested and grateful.

My usual charging rate was between 32 and 78, with occasional <20 and >90. I will be paying far more attention to the lower end of 32 and try to keep it above 45%

I interpret the stress from the increased visual separation on the graph, between the SoC (purple bar) and my function of the voltage (purple line) once the SoC it is below 50% and a battery voltage of approx. 3.8v

I can provide the spreadsheet of date values etc.

UPDATED Graph 20th March

It’s seems pretty clear that once the Service test shows the battery’s State of Charge below 50% the voltage hasn’t dropped at any linear rate and I have not been able to produce an argument that make the SoC and voltage align.

So the voltage appears reasonable [pink/orange bar] but the declared capacity drops rapidly. This again puts the effective battery’s capacity at a rapid decline around 50% SoC

The Pink bar shows the battery voltage ranging between approx 4.25v and 3.75

The large space between the f(v) and SoC between data points 42 and 50 are due to Rapid charging where a high voltage was being applied.