Latest E400 BMS update appears to have reduced usable capacity.

The recall was done on my 2018 MY recently. Prior to the update, my SOH was about 101%. I calculate it using displayed SOC percentage before and after charge, mileage between charges, and kWh/mile between charges. The results vary a little, because of the poor granularity of the data, but are reasonably consistent. The resulting capacity in kWh is then expressed as a percentage of 30 kWh (the usable capacity) to give the SOH. I also record GOM before and after charge, and calculate "GOM pessimism".

Since the update, the SOH has dropped to about 92%,. The GOM pessimism has reduced correspondingly. In both cases, the change is marked, not a gradual movement. The explanation I have arrived at is that the relationship between the real SOC in Ah and the displayed SOC in percent has been altered, and the GOM algorithm correspondingly altered so that the displayed range appears much as before (which it does). The data shows that the usable capacity has been reduced from 30 kWh to about 27.5 kWh, as the BMS will not charge over the 100% displayed value.

Another item of confirmatory evidence is that the 5hr 20min charge (with my wall box set to 16A) I usually employ to get approximately 50% SOC increase, now gives 58-62%. Some variation can be expected, mainly due to ambient temperature, but the noticeable step change is not linked to a marked shift in the weather. I do not believe the box is providing more Ah, so the change must arise because of an alteration of displayed %age charge.

I think KIA may have done this to extend the battery life, as the 70% SOH replacement value would appear to have been altered from 21 kWh to about 19.25 kWh. It may also have benefit in reducing the probability of dangerous overheating, which is the stated purpose of the recall.

I would be interested in knowing if anyone can confirm my observations. One way would be to compare cell voltage values at 100% SOC before and after the update.

The recent recall updated the BMS software. It is quite likely that the algorithm used by the BMS has changed. The PIDs we use to query the BMS also sometimes change.

But the GOM software is in the Navi computer. The trip data is stored here. The software for this has not been changed. The change must be that the BMS is sending different data for the SOC at the start and the end of a trip.

The SOH that should be used is from the original usable capacity of 30kWh. This is what the battery warranty applies to. It would not be okay for them to lower the 70% SOH replacement value by later artificially reducing the usable capacity.

JejuSoul said:

... It would not be okay for them to lower the 70% SOH replacement value by later artificially reducing the usable capacity.

Click to expand...

I quite agree. I will watch SoulSpy for when the reported SOH drops below 100% and then check my value for capacity. As Spy uses the SOH value computed by the BMS (which is presumably also used by KIA for warranty replacement), that should reveal whether they are playing it straight.

Do you perhaps have a record of cell voltage when fully charged before the recall was applied? Unfortunately, I do not.

Previously I have written this :- Analysis of a replacement battery.

Also of note - a MY2018 30kWh Soul EV has a final resting voltage at 100% SOC of 410.0V
This has 100 cells, each charged to 4.10V
My car has 96 cells, each charged to 4.14V

I assume this means there is a much larger buffer on the MY2018 30kWh Soul EV than a MY2015 replacement battery 27kWh Soul EV.

Click to expand...

The data came from 3 cars.
My blue 27kWh 2015 Soul EV. Original BMS. Data read 4 years ago. SOH = 96%
My white 27kWh 2015 Soul EV after replacement battery. 2nd BMS. Data read 4 years ago.
Norwegian 30kWh Soul EV. Original BMS. Data read 6 years ago.

There have been plenty of BMS updates in the intervening years. The latest being the 'Recall BMS'
that most of our cars now have. The BMS software is not the same. There is no way I can keep track of all the changes. Hence I no longer track BMS data for cars other than my own. Nor do I recommend trusting any app that gives BMS data, other than the one that Kia itself uses.

What I do recommend if you intend keeping the car for the long term is to track the range data over many seasons. This would give a real trendline of the car's usable capacity to compare the BMS data against.

Thanks, the data for the Norwegian Soul is just what I need. I will report when I have next done a 100% charge.

Well, I have done a 100% charge , and the battery voltage is 413.6, with all cells reading 4.12 volts. This was after 12 hr from full charge end. The reported SOH, stated as read from the BMS, is 100%. All data from SOULEV Spy.

This does not support my theory. I will have to search for another explanation.