Is this SoH OK?

[Susanna]

@Data - I really appreciate all your words of wisdom re. the scanner/apps etc., but I have sent it back to Amazon. It’s just too much of a faff! I gave up.

 

[decrep]

@decrep - weirdly, I did have to wipe over the reg plates on my MG yesterday, as they (like the rest of my car) were really filthy. And I was in a hurry…….

So do we have a psychic connection of some sort?

 

[Susanna]

So do we have a psychic connection of some sort?

We must have!

 

[doubledroz]

I bought a 71/2022 Mk2 ZS EV about a year ago. I have just installed the eZS app (great app!) and it tells me that the battery SoH is 85.4%. Is this normal for a 4-year-old car?

It doesn't appear anyone has answered your answer to the question of SoH for an X year-old car MG ZS EV, but there's a discussion on this forum - MG ZS EV MK2 - LFP (standard range) - Battery SOH Theory | MG ZS EV Forum - about the MG ZS linearly applying a SoH degradation percentage every single day.

I think that, with the LFP, the system has trouble working out what the real degradation is, so just arbitrarily applies a number until it learns otherwise.

I've got a 2022 Standard range (LFP), and that is reporting ~89% after being driven for three years. The distance doesn't seem to matter at all. The BMS just says "this is number".

The equalisation charge should help you, as people were reporting sudden jumps in their reported SoH from the OBD reporting apps.

I've not managed to do a proper equalisation charge, so my number is still going down, by the same amount, each damn day. If battery degradation is not linear, then I definitely shouldn't've lost this much by now.

According to random info across the internet, slow charging counts as anything between 0kw - 7kw, so if you ran it down to "low" battery, a 7kw would see the car charge be full and equalised in MUCH less time than the trickle charger supplied with the car.

I went from 0% displayed charge to 100% in 9 hours and 26 minutes, with the equalisation still happening. I had to stop it to leave unfortunately, but I know the car accepted ~48.5kw during that time.

The iSmart app wasn't reporting any charging speed, but the charger I was connected to definitely was!

 

[Data]

It doesn't appear anyone has answered your answer to the question of SoH for an X year-old car MG ZS EV, but there's a discussion on this forum - MG ZS EV MK2 - LFP (standard range) - Battery SOH Theory | MG ZS EV Forum - about the MG ZS linearly applying a SoH degradation percentage every single day.

I think that, with the LFP, the system has trouble working out what the real degradation is, so just arbitrarily applies a number until it learns otherwise.

I've got a 2022 Standard range (LFP), and that is reporting ~89% after being driven for three years. The distance doesn't seem to matter at all. The BMS just says "this is number".

The equalisation charge should help you, as people were reporting sudden jumps in their reported SoH from the OBD reporting apps.

I've not managed to do a proper equalisation charge, so my number is still going down, by the same amount, each damn day. If battery degradation is not linear, then I definitely shouldn't've lost this much by now.

According to random info across the internet, slow charging counts as anything between 0kw - 7kw, so if you ran it down to "low" battery, a 7kw would see the car charge be full and equalised in MUCH less time than the trickle charger supplied with the car.

I went from 0% displayed charge to 100% in 9 hours and 26 minutes, with the equalisation still happening. I had to stop it to leave unfortunately, but I know the car accepted ~48.5kw during that time.

The iSmart app wasn't reporting any charging speed, but the charger I was connected to definitely was!

Yes, SOH is dynamic. The SOH figure applies only at the time of checking & might be better or worse next time. Although generally it should not vary by large amounts. If a battery is equalised correctly on a regular basis the SOH will be quite stable & you retain a good range & state of health for much longer. SOH can also improve a little on cars that have not been equalised correctly over a period, or not been equalised at all if equalisation is carried out quite frequently for a period of time.

 

[Jomarkh]

At what SOC is it best to measure SOH?
Just after a balance charge at 100% or after driving and a lower SOC?

 

[JohnV6]

It shouldn't matter.

 

[Data]

It's generally accepted in the battery engineering world that checking SOH at 100% charge after an equalisation charge gives the ultimate SOH reading for obvious reasons. Doing it at lower SOC won't be as accurate. I tried this myself & obtained two different readings.

 

[MickeySw]

I tried this myself & obtained two different readings.

Curious, how much time did pass between the two readings and what was the actual difference?

 

[Data]

Curious, how much time did pass between the two readings and what was the actual difference?

Hello Mick, yes the time period between the two readings was 3 days. I recorded 100% SOH an hour after a full equalisation/balance charge in near freezing conditions. Three days later at 39% SOC & near freezing conditions my SOH was showing as 99.4%. Hardly any difference but as batteries age & cover more miles it seems this difference increases a bit. My dealer had checked my SOH 6 weeks earlier at a SOC of 66%. That SOH reading was 100% in near freezing conditions. A friend with a 3yr old long range ZS has 97% after a full equalisation charge & at around 45% gets a reading of 95.5%. His car has covered over 50,000 miles though. It was his readings that prompted me to check mine. I did this purely out of curiosity. I'm not concerned about battery SOH.

So, what does this tell us? SOH is dynamic. It is dependent to a degree on battery voltage. It is influenced by battery temperature. A lower reading one day may be higher the next. So a few variables appear to affect the figure. Does it matter? No.
EDIT: Just to mention that checking my own battery SOH once again a couple of weeks after all the above showed a reading of 100% SOH at 48% SOC.

 

[Lovemyev]

It is influenced by battery temperature. A lower reading one day may be higher the next.

The ambient temperature plays a big part on HV battery performance and its charging rate ability.
This is the reason why the battery can be brought up the ideal temperature prior to taking on a rapid charge, by the use of the battery heater provided.

 

[MickeySw]

So, what does this tell us? SOH is dynamic. It is dependent to a degree on battery voltage. It is influenced by battery temperature. A lower reading one day may be higher the next. So a few variables appear to affect the figure. Does it matter? No.

Interesting, I always thought that while a battery’s capacity is dynamic the calculated SoH is steadily decreasing according to a degradation model (mainly based on age and no of charge cycles)?

Only when one recalibrates the BMS (measuring current capacity and comparing it with the ‘spec’) is the SoH corrected?

Your observations seem to suggest that MG is adjusting SoH based also on environmental factors unlike other manufacturers?

 

[Data]

Your observations seem to suggest that MG is adjusting SoH based also on environmental factors unlike other manufacturers?

It's the same on our E-Niros & even the Leaf. It's also so very dependant on whether someone has balanced the battery at the point the SOH is checked. Since all car batteries are affected by the same variables I doubt MG are doing anything differently to other manufacturers.

 

[MickeySw]

It's also so very dependant on whether someone has balanced the battery at the point the SOH is checked.

If you mean after a BMS calibration, certainly, but why would simply balancing the cells affect SoH?

Since all car batteries are affected by the same variables I doubt MG are doing anything differently to other manufacturers.

The SoH on our MG5 has steadily declined since we got it in Summer 2022, however it has now ‘plateaued’ out around SoH 95% for the last couple of months which I believe is typical for NMC cells.

If the SoH is seasonally adjusted I would expect significant changes not merely a few %. I have also not seen variations @ different SoC values.

Maybe the MG5 is different, but it behaves exactly ‘like it should’??

 

[Data]

Bear in mind all of our batteries are behaving as they should. There is no seasonal adjustment, it appears just a small effect on results from temperature differences. SOH isn't affected by temperature in quite the same way as SOC/Range but it does have a small, sometimes very small influence as can be seen by anyone doing checks.

If a battery is out of balance & needs equalising, the battery capacity is affected. This might be by quite a bit, or just a little. It depends how well the battery has been looked after. This also seems to affect SOH readings unless a full & proper equalisation is completed. The BMS knows the original capacity, so filling the battery & equalising/balancing is the ultimate SOH measurement as the BMS can see how much of the buffer is being used, or indeed if the original buffer is still present.

When my dealer carried out a SOH check they noted the reading is dynamic & may not be totally accurate at 66% SOC (the level of my SOC). This statement appears to be true.

 

[doubledroz]

After my first incomplete equalisation charge (I had to leave!), my SoH reported at 90.1%, and then a second slow charge later in the week got me to 90.55% - I imagine that my battery was simply never properly balanced.

An interesting thing is that the iSmart App wasn't reporting the balancing charge - it was simply reporting 100%, and not showing the watts in.

The charger itself was reporting 2kW, which I thought was something to note for the future.

 

[MickeySw]

I imagine that my battery was simply never properly balanced.

Any chance you have the current min/max cell voltage values?

 

[Data]

After my first incomplete equalisation charge (I had to leave!), my SoH reported at 90.1%, and then a second slow charge later in the week got me to 90.55% - I imagine that my battery was simply never properly balanced.

An interesting thing is that the iSmart App wasn't reporting the balancing charge - it was simply reporting 100%, and not showing the watts in.

The charger itself was reporting 2kw, which I thought was something to note for the future.

Repeating the balance charge again quite soon after running the battery down to just below the 'low battery' warning may further improve your SOH figure. I've seen on a Tesla a 2% SOH improvement after 3 consecutive balance charges. A Tesla displays the individual battery cell voltages graphically. You can zoom in on the screen to observe how balanced the cells are. After the first equalisation/balance charge you could clearly see the cells were still unbalanced. As mentioned above it took a total of 3 balance charges to level them off & improve SOH. The bonus was also an increase in range.

 

[doubledroz]

Any chance you have the current min/max cell voltage values?

I'll try and remember to take a screenshot through the eZS app when I jump in the car today.

I am charging from just above the low battery warning today (25%), so it won't be too helpful, but I'm mostly sure it'll make a difference.

My first slow charge was from 0% (!) which wasn't intended, but just how it happened - that's the one where the equalisation charge was cut short by me..

in the 0% drive, ABRP was showing me a different SoC than the display SoC, so I went with the ABRP one (I think I would've had about 3% real SoC)

Repeating the balance charge again quite soon after running the battery down to just below the 'low battery' warning may further improve your SOH figure. I've seen on a Tesla a 2% SOH improvement after 3 consecutive balance charges. A Tesla displays the individual battery cell voltages graphically. You can zoom in on the screen to observe how balanced the cells are. After the first equalisation/balance charge you could clearly see the cells were still unbalanced. As mentioned above it took a total of 3 balance charges to level them off & improve SOH. The bonus was also an increase in range.

Yeah, I'm pretty confident the SoH will keep improving - 11% degradation on 3 years of usage seems way too high for an LFP battery, so I think it's just the arbitrary calendar daily 0.01% that the BMS knocks off on the gen2 ZS

 

[Everest]

This is all a bit academic really, though not that academic from a scientific point of view.

We first need to establish what SOH is intended to mean and how it should be measured.

In my opinion, SOH should be a representative figure for how good the battery's maximum capacity is now, compared to an original (100%) SOH when it was new.

Therefore, my 2p's worth is...

a) the SOH should gradually decrease over the battery's lifetime as a result of internal chemical degradation as a result of calendar and cyclic ageing.

b) the SOH should temporarily vary due to effects such as cell balance; as an imbalanced pack will not be able to hold as much charge as a balanced pack.

But..
c) the SOH should not vary due to SOC; it should be calculated from the last full charge cycle.

d) the SOH should not vary due to external temperatures. Although low temperatures will reduce overall capacity, such a reduction would also occur with a brand-new battery.

However, any reported SOH will need to be taken with a pinch of salt because, for EV applications, manufacturers build in a hidden "upper" buffer of unusable capacity. Hence any significant degradation in SOH can be mitigated by the EV's BMS software 'releasing' some of that buffer in to general usage so as to reduce the apparent degradation of SOH to the average user. So, without knowledge of the amount of upper buffer that has been deployed, the SOH is somewhat meaningless.