SoH/Stated range trends?

[Egbert]

I've had my 2018 BEV since Feb 2021. I've casually looked at State of Health, Kapa Max, and kept an eye on real-world range over the years. I also signed up with Recurrent.com just for giggles, they send me a monthly report.
Over the last several months, I've noted that my "score" with Recurrent has dropped quite a bit. One thing I did around New Year 2024 was used BimmerCode to program a few things I like on the car, including defaulting to Eco-Pro mode. Since then, I have noticed that the discrepancy between the remaining range on the BMW App and the dash when I start up has gotten larger. I assume the app shows me Comfort mode range, and the car is showing Eco-Pro mode, but the delta can sometimes be ~30 miles at full charge. Seems strange, since I'm not aggressive with driving or with HVAC. If I drive in Comfort mode for a day or two, the gap between ranges closes quite a bit, but then will stray when I'm in Eco-Pro all the time.

My first mi3 check was in April 2021, SoH was reported at 93%, 91% in July 2022, and 89% yesterday. I haven't really noticed any change in useful range, but maybe I'm starting to notice that the last 30% goes more quickly than the upper/middle 30%? I haven't looked closely at this yet, though.

Is anything out of the ordinary here? The car's "born on" date was July 2018.

 

[eNate]

I haven't really noticed any change in useful range, but maybe I'm starting to notice that the last 30% goes more quickly than the upper/middle 30%?

When you're looking at this, is this in one long distance go? Or the culmination of multiple trips?

I tend to only consider "usable range" a single leg full to empty excursion. There are a lot of variables at play that can throw off this range figure when driven over multiple sessions.

 

[Egbert]

This is almost always multiple trips. But it's the same trips- work, home, swim practice, home... rinse, repeat. The strange thing to me is how it seems like the Comfort Range deviates from the Eco-Pro (that is now default mode). I guess that's mostly a curiosity.

Do you find the 89% SoH to be out of line for a 2018 94aH with 52k miles? I always charge at home, only used DC charging perhaps 10-12x in the 3+ years I've owned it. I generally stay in the 20-100% range, and rarely let it sit at that high charge level.

Maybe I'm just rambling, no real issue...

 

[eNate]

It's hard to say. I have an estimated battery health of 90% -- a 2021 with 30,000 miles. At this exact moment my car is plugged in to a charger and the battery is at 37% and est. 50 miles, or about 135 miles at full charge. That's with nice weather and my normal 12 mile each way commute. 135 miles is exceptionally low, that's what I would get in my 2017 with a full charge.

However, in this same car, just three weeks ago, I charged to 100% and took the car out on a road trip, and I my estimated mileage quickly climbed back up to about 180 on a full charge, and my trip / charge data via the BMW app backs that up.

So for me it's two very different use cases, everyday hopping around town where I just plug in and maintain and don't really pay attention to range, vs. road trips where I'm stretching a full battery for a longer distance.

 

[Clanduncan]

After a year or so of only charging to 90% or so, and after all the articles/opinions I've read, I recently started charging to 100% each time again. BMW (in my 94Ahr rex at least) only let you use around 85% of the battery capacity anyway, see the picture for SOC while the car tells me I'm at 100%. So IMHO to allow top end cell balancing seems healthier to me long term.
The following screenshot from the Electrified app (with veepeak odb2 dongle) seems to suggest my battery is fairly healthy. It shows 87 of 94 Ahrs still available, or an SOH of 86%. Do others agree, what are your comparisons?

 

[alohart]

After a year or so of only charging to 90% or so, and after all the articles/opinions I've read, I recently started charging to 100% each time again. BMW (in my 94Ahr rex at least) only let you use around 85% of the battery capacity anyway, see the picture for SOC while the car tells me I'm at 100%. So IMHO to allow top end cell balancing seems healthier to me long term.
The following screenshot from the Electrified app (with veepeak odb2 dongle) seems to suggest my battery is fairly healthy. It shows 87 of 94 Ahrs still available, or an SOH of 86%. Do others agree, what are your comparisons?

The state of health suggests that your battery pack has lost 14% of its nominal new capacity. Unfortunately, the BMS seems to report the maximum actual charge level, 85.3% in your case, as a percentage of the nominal new actual charge level when no cell degradation had occurred rather than as a percentage of the current actual charge level when cell degradation has occurred. This suggests that the top-end buffer has increased in size to 14.7% which must not be true because the cell voltage, 4.13 V, is near the maximum cell voltage possible. The cell voltage would be considerably lower at an actual charge level of 85.2%. At an indicated 100% charge level, the actual charge level must be unchanged at ~95% as indicated by the cell voltage.

Another way of expressing this is that the BMS seems to keep the size of 1% of the usable capacity, 27.2 kWh/100 percent = 0.272 kWh/percent, constant regardless of how much cell degradation has occurred. This leads to a maximum actual charge level, 85.3% in your case, that is inconsistent with a high cell voltage, 4.13 V.

The difference in minimum and maximum cell voltages is only 0.01 V which indicates excellent cell charge level balance. This suggests that charging to an indicated 90% (an actual charge level of ~85%) is sufficient for the BMS' passive cell charge level balancing to occur. Charging to an indicated 100% shouldn't improved the cell charge level balance but would increase the cell degradation rate a bit. I don't know whether that would be noticeable, but I plan to keep our i3 as long as possible, so I try to minimize the cell degradation rate by not fully charging routinely unless I might need the full range.

 

[eNate]

Re: Art's comments above, here is a BMW training slide re: the 60 Ah variant (click thumbnail for full sized image).

396v is listed at the max voltage but I see 398v listed for your 94 Ah / 33 kWh battery.

398v ÷ 96 cells = 4.14 volts per cell, which is the 100% charge for a nominal 3.75v NMC cell.

I continue to be confused by how the i3 calculates the reported SOH % because it always seems lower than reality based on range.

 

[Clanduncan]

Alohart/eNate,
Thanks for that info and the explanations. Seems to show my car is in pretty good shape battery wise. In the 3.5 years I've had it I've not seen any appreciable drop in range, apart from the usual seasonal variations. For me that means 100-130 miles and 60 to 100 on the rex. Not bad for a near 8yr old car.

 

[alohart]

In the 3.5 years I've had it I've not seen any appreciable drop in range, apart from the usual seasonal variations.

That's the data that matters most. If an EV satisfies one's use case , it's good enough. We sold our 2014 i3 BEV when its range decreased so much that we could no longer comfortably use it as we wished.

 

[eNate]

What's missing from the Electrified data that I can read on my ID.4 is the battery MEC – maximum energy content.

This isn't a hard and true number. Like with the i3, it's best to drive that car down onto the single digit SOC range then take it back up to 100% indicated, let the cells balance and top off, then take a reading. But it gives the user a good idea where the actual state of charge lies, and how much useable capacity has been lost since new / rated capacity.

 

[Clanduncan]

The battery kappa max figure, via hidden menus, sounds like it does a similar function. On the i3 it really only is a 'guide' though, useful to spot trends perhaps but not absolutes. On mine it varies, again seasonally, from 27.2 to around 28.