High Rates of SoH degradation in Taycan

[Reg]

From the linked thread

which include 7 users from a German Forum (courtesy @rs38) and a single data point from a Porsche marketing/news article. Clearly not a statistically significant sum

Agreed. this isn't significant.

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[ben1]

I did further analysis on all the chargings I have made. I have charged the car for 187 times, and I selected only such where I have charged 60% or more (77 different sessions).

I calculated the capacity of the battery using the the statistics I have using this formula :
Capacity kWh = ((Consumption kWh/km * Distance driven km) / Consumed capacity %)

To create a trend line, I selected the median value of each month from the data to the graph below.

The end result is interesting, it looks like the car has had net capacity of 89 kWh in the beginning and now it is closer to the spec of net capacity at around 83 kWh.

Also interestingly, the trend follows quite well the SoH measurements I have taken during the ownership (red dots in the graph)

This is very interesting.
This could mean that the SoH 100% reference that the Taycan is using is not the netto maximum, but the bruto maximum. This could explain why the initial degradation is so fast and why the numbers are about 5% less than Tesla.

Since the initial degradation is so strong and also very very early in the age of the battery, I am guess in there is something wrong with the initial reference point.
It would explain the behaviour we are seeing.

 

[WasserGKuehlt]

This is very interesting.
This could mean that the SoH 100% reference that the Taycan is using is not the netto maximum, but the bruto maximum. This could explain why the initial degradation is so fast and why the numbers are about 5% less than Tesla.

Since the initial degradation is so strong and also very very early in the age of the battery, I am guess in there is something wrong with the initial reference point.
It would explain the behaviour we are seeing.

The video shared earlier in this thread by @jvincent explains exactly this, among a few other tidbits. Caution: it is, indeed, long and rambling, but at least the scenery is okay.

 

[ben1]

If it is true that that SoH is using the wrong reference point (bruto capacity instead of netto). It might be more correct to use the 'energy capacity' reported by the ODBII-app and divide it by the netto maximum capacity.

My ODBII-app reports about 91% SoH. And 67,5 kwh max capacity.
Dividing 67,5 kwh by 71 kwh (=the netto capacity of the standard battery) is 95%.
This is in line with what other automakers report.

 

[rs38]

the best proof that the Taycan SoH value is not purely degradation is the quite big recovery from winter to summer. The BMS can only estimate the fitness level especially if you do not always use the full span of capacity.
IMHO the best way to compare capacity and wear over time is charging from 0-100 ideally with low power DC (20kw) but I guess AC losses are not too much and stay constant.
New battery should be like 86.7 kWh + 5-10% AC OBC+standby+heat losses.
(I cannot remember my car did this in the last 2 years)

 

[ciaranob]

the best proof that the Taycan SoH value is not purely degradation is the quite big recovery from winter to summer. The BMS can only estimate the fitness level especially if you do not always use the full span of capacity.
IMHO the best way to compare capacity and wear over time is charging from 0-100 ideally with low power DC (20kw) but I guess AC losses are not too much and stay constant.
New battery should be like 86.7 kWh + 5-10% AC OBC+standby+heat losses.
(I cannot remember my car did this in the last 2 years)

Good point (and speaks in part to other comments re consumptive Kw hours vs range vs SoH in prior posts).

I was seeing a 10% shift (predicted ranges) from Summer to Winter - not deep enough into Summer charges in this second year yet to compare but have not reached those highs I had prior as yet - however with some long trips and more extensive discharge-recharge to 100% I suspect I will.

Need to update some metrics on bottom but to date 48 AC charges all to 85% and only 13 DC charges (also need to clean-up the chart a bit for last entries which shifted timescale!).

 

[Tooney]

What is the purpose(s) of recording and viewing your Taycan's SoH measurements and trends over time? What actions/decisions will someone take based on this information?
Range and performance (or lack thereof) are usually readily apparent, and may cause the owner to make decisions or take action.
What does the SoH trend do?

 

[gtm]

Using SoH to plot apparent battery degradation provides a consistent data point. I suspect what that number really represents is known only to the Porsche engineers.

There are 3 different SoC readings available via Car Scanner. SoC HR, Display and True. At a 100% charge those numbers were 96.86%, 100%, 97.75% respectively. The reported "Battery Energy" has to be a best guess measurement since I don't believe this is something that can be measured statically and the accuracy of the reading will drift over time. But assuming it is close to actual the displayed full capacity at 100% was 82.55 kWh. Using the SoC HR (96.86%) a calculated full capacity is 85.23 kWh, and with SoC True (97.75%) is 84.45 kWh. At 4182 miles I show a 95% SoH. So calculate SoH from a 93.4 kWh pack and I'm down 9 to 11% depending on which SoC number you use. Do it from the 83.7 kWh available figure and I've either gained a little capacity or am down 1%. Do it from the 86.7 kWh figure frequently referenced as the base line for calculating SoH (has Porsche quietly reduced the buffer and made more available?) and my battery has lost from 1.70% (HR), 2.60% (True) or 4.79% (Display). None match up with a 5% loss but Display is close. A lot depends on whether the "Battery Energy" reported by Car Scanner is gross or net (a very big difference). Which of the SoC figures are accurate? Unless someone has definite knowledge of what is used to calculate SoH I'm not considering it necessarily accurate but rather a consistent reference point. I have a 6 mv variance between high and low cells which is a minimal difference. I now have a displayed capacity at 100% for reference. Those are what I will monitor to assess how my battery ages.

@ciaranob (and maybe @rs38) you are the one accumulating a ton of data. Do you know which measurements are actually used and/or accurate? SoC HR, vs Display vs True for example. Makes me wonder how Porsche is calculating degradation for warranty purposes.

 

[ciaranob]

From the linked thread

#16
"which include 7 users from a German Forum (courtesy @rs38) and a single data point from a Porsche marketing/news article"

Agreed. this isn't significant.

Not sure what your point is here in 'selective' cropping and pasting - I'd suggest data that includes 77 readings from 50 cars spread over 3 years of ownership is not entirely insignificant but as I already stated, statistically challenged. I guess you agree

The full sentence for context taken from the baseline thread:

Quote:
These data from 50 cars with 77 readings which include 7 users from a German Forum (courtesy @rs38) and a single data point from a Porsche marketing/news article. Clearly not a statistically significant sum but interesting nonetheless and some trends developing - in particular the known slightly higher degradation of SoH in hot climates.
Unquote.

 

[ciaranob]

Using SoH to plot apparent battery degradation provides a consistent data point. I suspect what that number really represents is known only to the Porsche engineers.

There are 3 different SoC readings available via Car Scanner. SoC HR, Display and True. At a 100% charge those numbers were 96.86%, 100%, 97.75% respectively. The reported "Battery Energy" has to be a best guess measurement since I don't believe this is something that can be measured statically and the accuracy of the reading will drift over time. But assuming it is close to actual the displayed full capacity at 100% was 82.55 kWh. Using the SoC HR (96.86%) a calculated full capacity is 85.23 kWh, and with SoC True (97.75%) is 84.45 kWh. At 4182 miles I show a 95% SoH. So calculate SoH from a 93.4 kWh pack and I'm down 9 to 11% depending on which SoC number you use. Do it from the 83.7 kWh available figure and I've either gained a little capacity or am down 1%. Do it from the 86.7 kWh figure frequently referenced as the base line for calculating SoH (has Porsche quietly reduced the buffer and made more available?) and my battery has lost from 1.70% (HR), 2.60% (True) or 4.79% (Display). None match up with a 5% loss but Display is close. A lot depends on whether the "Battery Energy" reported by Car Scanner is gross or net (a very big difference). Which of the SoC figures are accurate? Unless someone has definite knowledge of what is used to calculate SoH I'm not considering it necessarily accurate but rather a consistent reference point. I have a 6 mv variance between high and low cells which is a minimal difference. I now have a displayed capacity at 100% for reference. Those are what I will monitor to assess how my battery ages.

@ciaranob (and maybe @rs38) you are the one accumulating a ton of data. Do you know which measurements are actually used and/or accurate? SoC HR, vs Display vs True for example. Makes me wonder how Porsche is calculating degradation for warranty purposes.

I think we're 100% on the same page - addressed your observations I think largely in this response #14 in this same thread.

Again, no one on this forum knows exactly what algorithm Porsche's PCM is using to 'estimate' (however crude/with what error) the SoH reading is that the OBDII tool access's but as in my prior post, and to what you re-state here, it is still a consistent 'measure' and resultant output data to date make 'sense' in respect seeing varying degradation trends in for example climate zones etc from published comments from manufacturers and other sources. More a question perhaps of how much will these OBDII plotted curves shift as compared to proper factory testing of the HV batteries true SoH.

Again we don't yet have the data to answer that - Porsche, Tesla etc of course do - I did read that a large chunk of the published Tesla data in my chart overlay was supposedly taken from a 'leak' of Tesla's own testing so perhaps it represents true factory data? Again needs to be confirmed and we'd hope that Posche's data might match (suspect it prob does).

Also mentioned prev re +/- 1-2% SoH variations between summer/winter readouts in the OBDII and in fact between different charging sessions.

Finally as posted in the Baseline thread (post 1) - in respect what the OBDII tool is most likely reading - quote:
Also remember that the SoH% is believed to be a % of, for example, the usable 83.7kW of the Performance+ 93.4kW capacity battery i.e. excludes the car's buffered/protected charge (see also more on this from forum member rs38 here #38 )
Unquote.

 

[npx]

And this is where I suspect we just don't have enough data/insight in the comparison between brands in respect how the buffers are managed, and together with other metrics, how the respective calculations are made in respect backing out a valid comparison.

There's enough expertise and knowledge in this Forum I further suspect that we might still be able to determine how valid that initial chart comparison is.

I'd love to see any more authoritative input for sure. nice work though

 

[Reg]

Not sure what your point is here in 'selective' cropping and pasting - I'd suggest data that includes 77 readings from 50 cars spread over 3 years of ownership is not entirely insignificant but as I already stated, statistically challenged. I guess you agree

I disagree that 50 cars out of over 100,000 (0.05%) sold is "not entirely insignificant".

I agree that it is "statistically challenged".

as I already stated

I have no idea why you changed the originally wording from "not statistically significant" to "statistically challenged" LOL.

 

[ciaranob]

I disagree that 50 cars out of over 100,000 (0.05%) sold is "not entirely insignificant".

I agree that it is "statistically challenged".



I have no idea why you changed the originally wording from "not statistically significant" to "statistically challenged" LOL.

This is rather sad if your 'position' boils down to semantics - LOL indeed covers it

So how many tests of any one measurement of anything classifies as statistically significant in your mind - this should be fun - please carry on.

 

[Jonathan S.]

What is the purpose(s) of recording and viewing your Taycan's SoH measurements and trends over time? What actions/decisions will someone take based on this information?
Range and performance (or lack thereof) are usually readily apparent, and may cause the owner to make decisions or take action.
What does the SoH trend do?

SoH is important for any EV if you want to calculate your range for a specific trip based upon a prior mi/kWh result from that same trip under the same wx, traffic, etc.
The GOM, by contrast, is performing the same calculation based upon some unknown look-back period plus unknown weighting algorithm (if any) combined with the route being navigated (if the driver has input that).

 

[Tooney]

SoH is important for any EV if you want to calculate your range for a specific trip based upon a prior mi/kWh result from that same trip under the same wx, traffic, etc.

How do you calculate your EV range using SoH? Could you show an example of the calculation?
Since this forum is about Taycans, what is the relationship between a Taycan's range and its SoH?
Is there any range/SoH relationship?

I do not understand the importance of tracking SoH in my Taycan, and how knowing my Taycan's SoH and its trend are useful to me as a driver.

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