Help with SoH reading

[Mache_Nor]

Hey there!

Driver of a ER 2021 job 2 car, RWD, driven 100 000 km / 62 500 miles. Followed the tips of the forum by going very low and fully charge in 20C to get a correct reading of my battery’s SoH, however I am unsure what is correct.

First, the reading at full charge in 20C from car scanner (red image). Here the SoH is 89% (which would be roughly 81 kWh remaining possible battery capacity).

Secondly, also from same app (image 2), here the car claims to be 97% full with close to 86 kWh available power.

Thus, if I calculate 97% of 91 kWh that is roughly 88.2 kWh, and since it claims to be 85.65 kWh in battery it is 85.65 / 88.2 * 100 = 97% SoH. But… why does car scanner claim 89% while this calculation is 97%? 97% sounds too good while 89% too little, given I have been a real battery freak that does all the tricks in the book to make it last as long as possible.

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[alexgorod]

SOH != SOC

The first one is "State Of Health", and the second - "State Of Charge".

 

[Mache_Nor]

But isn’t SoH a measure of how much (potential) battery capacity the battery can hold when fully charged? That’s why I measure the capacity (SOC) and compare it to normal / new to calculate the SoH value. My math might be off so if I can calculate this differently I’m open for suggestions

 

[hybrid2bev]

I thought the 97% SOC is off of the full battery capacity of 99 kWh. So if a full ER battery including the buffer is 99kWh * .9705 actual SOC = the battery should be at about 96 kWh. You have 85.65kWh so 85.65 / 96 = 89% soh

 

[Teslaeata]

SoH is a measure of the condition of the battery not its charge, unrelated. Bit like an ICE engine, Ford’s wet camshaft drive belt engine for example which at 25,000 miles can still deliver same mpg as when new but is about to cut its own wrists in another 10,000 miles for no reason so its effective SoC or mph is still 100% at 25,000 miles but its SoH is c30% ?

 

[Mach-Lee]

91 kWh is the USABLE capacity when new, out of the 99 kWh total capacity. The actual SoC will never reach 100% or 0% because of the top and bottom buffers. You do not get to use the whole battery because that's bad for it. The bottom buffer is included in the energy to empty calculation. The car will run out of power and stop moving with 2-5 kWh remaining in the pack.

With 89% health you have about 81 kWh available to use for trips.

 

[Mache_Nor]

91 kWh is the USABLE capacity when new, out of the 99 kWh total capacity. The actual SoC will never reach 100% or 0% because of the top and bottom buffers. You do not get to use the whole battery because that's bad for it. The bottom buffer is included in the energy to empty calculation. The car will run out of power and stop moving with 2-5 kWh remaining in the pack.

With 89% health you have about 81 kWh available to use for trips.

Thanks. So if I understand right those 85-86kwh available power reading takes into account the bottom buffer? It’s 3% buffer on top, but do we know the bottom buffer? As of today I ran to 10% visual SoC (inside car) and car scanner claimed it was 11% left (which makes it a bit weird as that means I have 85% useable kWh outside buffer). Lastly, even if SoC and SoH is not 1-1 related it somewhat indicates the health of the battery; do you know the best way to gauge this or must I assume the 89% reading from car scanner is as good as it gets?

 

[Mach-Lee]

Thanks. So if I understand right those 85-86kwh available power reading takes into account the bottom buffer? It’s 3% buffer on top, but do we know the bottom buffer? As of today I ran to 10% visual SoC (inside car) and car scanner claimed it was 11% left (which makes it a bit weird as that means I have 85% useable kWh outside buffer). Lastly, even if SoC and SoH is not 1-1 related it somewhat indicates the health of the battery; do you know the best way to gauge this or must I assume the 89% reading from car scanner is as good as it gets?

The 89% is the best estimate of the battery capacity you can get. That's what you should use for calculations. ABRP will also use that value if connected to OBD live data.

Top and bottom buffers are variable and may change with age, but figure about 4% for each.

Sample range calculation: 91 kWh (new) * 89% health * 60% SoC Displayed ÷ 20 kWh/100 km efficiency * 100 km = 242 km of range remaining (assumes 25ºC ambient/battery temp, less in cold weather)

Anything more than that is overthinking. Only use displayed SoC not actual SoC for calculations or you'll run out dead.

 

[Mache_Nor]

The 89% is the best estimate of the battery capacity you can get. That's what you should use for calculations. ABRP will also use that value if connected to OBD live data.

Top and bottom buffers are variable and may change with age, but figure about 4% for each.

Sample range calculation: 91 kWh (new) * 89% health * 60% SoC Displayed ÷ 20 kWh/100 km efficiency * 100 km = 242 km of range remaining (assumes 25ºC ambient/battery temp, less in cold weather)

Anything more than that is overthinking. Only use displayed SoC not actual SoC for calculations or you'll run out dead.

Alright, thanks! I’ll continue my 70-30% driving then and I’ll try to reduce my worry of battery hehe. What I will actually do is to track all my driving in the app, then over time export it and read the SoH / degradation over time. Will be interesting to see if it slows down, as 11% on just 2.5 years seems excessive, especially when I only fast charge like 5% of all my charging, keep it in 70-30% charge level, lives in a cool environment, connected to charger when cold, parked in carport shade and precondition battery on the morning. Can’t do more to make it live longer.

 

[Mach-Lee]

Alright, thanks! I’ll continue my 70-30% driving then and I’ll try to reduce my worry of battery hehe. What I will actually do is to track all my driving in the app, then over time export it and read the SoH / degradation over time. Will be interesting to see if it slows down, as 11% on just 2.5 years seems excessive, especially when I only fast charge like 5% of all my charging, keep it in 70-30% charge level, lives in a cool environment, connected to charger when cold, parked in carport shade and precondition battery on the morning. Can’t do more to make it live longer.

FYI you should charge it from 15-100% in one session once every couple months to help calibrate the battery. If you charge to 70% all the time it has more trouble reading the capacity and SoH will read a little lower than actual to be safe. You’re doing the best thing for the battery, computer just don’t know what to make of it.

 

[Snakebitten]

Do what Mach-Lee suggests regarding occasional 15-100% charge. (L2 for me at home)

And watch Car Scanner SOH increase!
Whatever their algorithm is for calculating SOH, it's not as simple as I think we might think. And it absolutely can increase rather than only decrease.

 

[noway]

Has anyone ever seen the SoH increase after re-calibration? Mine is at 89.5%, after it dropped from staying a long time on 94.5%. Seems do only do 5% decrement at a time to me

 

[Mach-Lee]

Mine is at 89.5%, after it dropped from staying a long time on 94.5%.

That's because it wasn't updating properly on old software, hence the big drop post-update.

You might be able to get it to go up a percent by doing a calibration.

 

[Mache_Nor]

Has anyone ever seen the SoH increase after re-calibration? Mine is at 89.5%, after it dropped from staying a long time on 94.5%. Seems do only do 5% decrement at a time to me

Car type and distance driven? Just for comparison. Btw nice seeing other Norwegians here

That's because it wasn't updating properly on old software, hence the big drop post-update.

You might be able to get it to go up a percent by doing a calibration.

Speaking about that; do you think the EU vs US cars might be different which can affect the reading? As EU is usually 6-12 months behind US in terms of software (we have not received the easy access, 12V charging changes and UI OTA for example). Also, wasn’t there an discussion wether the famous (or infamous) OTA that was supposed to release some of the battery buffer for 21-models actually worked and some cars do not have this reduced buffer?

 

[noway]

Car type and distance driven? Just for comparison.

First edition at 161 000km. It is actually at 88.5% after checking again

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