i3 Battery charging - Degradation real life experience

[Steen2000]

Hi
I am looking to undeerstand how the i3 120Ah seem to cope with degradation?
Being not able to limit charging to less than 100% seems unhealthy?
I assume there must already be numerous posts on battery degradation and peoples experiences?

 

[alohart]

I bought a 2014 U.S. i3 BEV new. After about 7 years and less than 13k miles, its 60 Ah battery pack had lost about 25% of its new nominal usable capacity.

I replaced the 2014 with a used 2019 BEV (I'm the third owner). After almost 4 years and ~32k miles, its 120 Ah battery pack shows no signs of capacity loss.

I think that the 94 Ah and 120 Ah battery packs are much better with respect to degradation than the 60 Ah battery pack.

 

[jfran2]

I wouldn't worry about charging at less than 100%. BMW equipped the i3 with a very robust BMS (Battery Management System). Although your gauge may say 100%, the BMS controls the actual charge of the battery.

 

[eNate]

I'm an 80% kinda guy. BMWs BMS is a decade old compared to what's available on EVs being introduced today, and all of these newest cars – including the new BMW EVs – come with user-selectable charge management. The new BMWs even allow charge current selection (not just "reduced rate" like on the i3)

I believe that BMW was attempting to make the i3 ownership experience trouble-free when they decided to leave this out, and adding it in later would be an admission of their oversight, and potentially open them to liability – not to mention paying to update software on a lot of cars.

I hope my 120 Ah battery had better chemistry and lasts longer than the original 60 Ah models.

One complicating factor in assessing this is that 120 Ah batteries are used less (on average) than their 60 Ah counterparts. In other words, if the average daily distance driven is 40 miles, then the early batteries were using 50% of their capacity daily, where the 120 Ahs are only using a quarter of their capacity. That right there should account for the larger battery degrading at half the rate of original.

Of course the i3's generous buffer helps, but it's divided between the top and bottom of the pack, so 100% indicated is really 95% or so – nowhere near 80%.

Anyhow I'll continue to manage my 80-ish% charge manually, no biggie, I also don't sweat it if I occasionally charge to 100%. I hope this pays off as the car ages.

 

[agzand]

Hi
I am looking to undeerstand how the i3 120Ah seem to cope with degradation?
Being not able to limit charging to less than 100% seems unhealthy?
I assume there must already be numerous posts on battery degradation and peoples experiences?

Try using departure time charging as much as you can. Also if you are in extreme hot/cold environment try parking in a garage or shade as much as you can. Besides these two things do not worry about degradation, it is not an issue for newer batteries.

 

[JohnKelly]

My 60ah 2015 has almost 88,000 miles on it. I charge to 100% at home regularly and DC fast charge a fair amount. I have driven the same route hundreds of times in the last 5 years. Not a hint of ANY degradation of the battery. I reach the same milestones at similar temperatures and times of the year. The best I ever had left at this one spot was 75% in a 2016 BEV I had for just under a year. It weighed ~300lbs less than my REX and it had only about 14,000 miles on it. I was really trying to get the absolute most range out of that particular trip in the BEV... pulling over to let traffic go by, going slower up hill and faster down hill etc. In my 2015 REX, I have arrived at that same spot one time with 74% in the heavier car without pulling over or going slower uphill etc. I was surprised. Recently I reached that spot with 72% left... also without trying to get the most out of the range by driving slow. I just drove normally. The battery in this car is amazing.

 

[alohart]

I'm an 80% kinda guy.

I share your charging protocol. Despite this, either the 60 Ah battery chemistry or its BMS trying to decelerate degradation by increasing the buffer sizes resulted in the loss of ~25% of its usable capacity after 7 years and only ~$13k miles of ideal EV driving conditions.

I owned a gasoline-electric hybrid whose BMS had no charge level balancing capability. This resulted in the battery pack being replaced twice under warranty due to severe charge level imbalance. I was concerned that routinely charging our i3 to ~80% would not allow its passive charge level balancing to do its job completely which could result in a loss of usable capacity. However, the mi3 smartphone app showed that the charge levels of all 96 battery cells were almost identical, so the i3's passive charge level balancing works well even when usually charging to ~80%.

Even though I have not read a single report of a 120 Ah i3 owner reporting significant battery pack capacity loss, I have continued charging to ~80% except when I might need full range. However, driving on Oʻahu where the longest round-trip distance is less than 120 miles and a predicted range of ~215 miles when fully charged (averaging 5.7 mi/kWh), I've never needed to fully charge. I do so periodically just to allow charge level balancing to proceed a little more quickly.

 

[MarkH]

I bought my 2016 94aH 33kWh BEV in 2019.
It's SOH was 28.6 kWh when I bought it.
I record the SOH each month.
The SOH has declined at a reasonably regular rate since mid 2019 to 27.4 kWh in mid 2023 (0.023% per month).
In the last two months it has "fallen off the cliff" and is now at 26.6 (0.400% per month)

What has changed in the last 2 months is that, instead of my usual routine of charging to about 80% whenever the battery discharged to less than 30% - maybe every 3 days, I now charge the car a little each night (using free power between 9pm and midnight).

I'm wondering if maybe the battery doesn't like the new regime? - or is it just chance?

 

[eNate]

I bought my 2016 94aH 33kWh BEV in 2019.
It's SOH was 28.6 kWh when I bought it.
I record the SOH each month.
The SOH has declined at a reasonably regular rate since mid 2019 to 27.4 kWh in mid 2023 (0.023% per month).
In the last two months it has "fallen off the cliff" and is now at 26.6 (0.400% per month)

What has changed in the last 2 months is that, instead of my usual routine of charging to about 80% whenever the battery discharged to less than 30% - maybe every 3 days, I now charge the car a little each night (using free power between 9pm and midnight).

I'm wondering if maybe the battery doesn't like the new regime? - or is it just chance?

Mark, have you run the battery down then charged it to full recently before checking reported capacity?

When a battery is living its life in the middle of its electrical capacity like yours is (mine too), the BMS can never be quite sure what the state is charge is – it's a good educated guess based on coulomb counting and resting voltage, but it's never perfect.

If you discharge down below 5%, the voltage "falls off a cliff" in a very signature way, and the same is true when you then charge it to 100 (indicated, of course). At this point, the BMS knows very accurately where the battery is, and how much charge went into it to get it there.

So I encourage you to do that: run it down then top it off, let it sit plugged in over the day so it can balance and re-top, then take your capacity check. Hopefully you'll be surprised with a boosted result.

 

[alohart]

eNate's suggestions are good.

Keep in mind that the usable capacity reported by the BMS is only an estimate, so the actual usable capacity is likely different. This is especially true because your battery pack hasn't been fully discharged and fully charged much which should improve the capacity estimate as eNate explained.

Also, cell charge level imbalance reduces the usable capacity temporarily whereas cell degradation would reduce capacity permanently. I haven't read any complaints about 94 Ah battery cells degrading rapidly as has happened with many 60 Ah battery cells. The i3's passive cell charge level balancing very slowly discharges those cells with the highest voltages when the battery pack isn't being charged or discharged (e.g., when an i3 is off). The discharge rate depends on the cell voltages, so the balancing rate would be higher at higher charge levels. Charging routinely to 80% might slow down the cell balancing rate enough that balancing might never complete which would reduce the usable capacity. eNate's suggestion to fully charge and then allow your i3 to remain off for several days would be worth trying.

When the i3 was first introduced, a group of British i3 owners attended a session held by BMW engineers who explained that cell balancing is so slow that a battery pack with very unbalanced cells could take many days or maybe even weeks to become fully balanced. I've been impressed by how well the i3's passive cell balancing works even though I routinely charged to only 80-90% rather than to 100% for the past 9 years. So it's probably unlikely that the charge levels of your battery cells vary much.

You are reporting the SoH of your battery pack which suggests that you might be using the iOS mi3 app, the Android electrified app, or one of BMW's Windows apps. If so, the minimum and maximum battery cell voltages, capacities, and charge levels should be reported. If the minimum and maximum are almost identical, cell charge level balance should be good.

 

[MarkH]

Thanks eNateand alohart.

Things are always more complicated than I have assumed!

Is it important to do both the discharge below 10% as well as the 100% charge - or, as alohart intimates, just the 100% charge?

My SOH figures are reported, not from any 3rd party app, but just the "hidden menu" function of the car itself.

 

[alohart]

Is it important to do both the discharge below 10% as well as the 100% charge - or, as alohart intimates, just the 100% charge?

For the BMS to be able to calculate its most accurate usable capacity, it would need to know when the charge level has decreased to a more certain charge level due to a faster voltage decrease at low charge levels as well as when the charge level has increased to a more certain charge level due to a faster voltage increase at high charge levels.

My SOH figures are reported, not from any 3rd party app, but just the "hidden menu" function of the car itself.

It would be worth installing the iOS mi3 app or Android electrified app, neither with a license fee, to be determine whether a significant charge level difference exists among all 96 battery cells. You would need to buy an OBD adaptor, either WiFi or Bluetooth, to allow your smartphone to connect to the adaptor when it's plugged into the OBD port on the underside of the dashboard to the left of the steering column.

I have seen as much as a 4 kWh difference in the Batt. Kapa. max readings over a fairly short period of time, so Batt. Kapa. max is not an especially accurate usable capacity estimate. However, you have been repeating these readings over time which makes at least the trend in values more significant.

 

[MarkH]

Thanks alohart

I have a VeePeak ODBCheck BLE.
Downloaded electrified.
Wouldn't connect - "ODB is out of range or switched off"
But BimmerCode and BimmerLink each connect.

Anyway, I'll deplete the battery and fully charge - leaving it charging overnight after getting to 100% and re-check the Batt KAPPA reading. See if it makes a difference.

 

[alohart]

Downloaded electrified.
Wouldn't connect - "ODB is out of range or switched off"\

It's too bad that this didn't work. Lots of good data would be displayed. I use mi3 so I can't make any suggestions about electrified. The error message suggests that the OBD port might not be on. If you haven't done so, try connecting when your i3 is in drive ready state. Or maybe the Bluetooth signal was too weak, so try moving your phone closer to the OBD port. Pretty lame suggestions, but that's all I got.

 

[MarkH]

Ran the battery down to 7.5% then charged it to 100% leaving it plugged in a further 5 hours.

Tried the VeePeak ODB again (and this time I turned the car on to READY).
It works

Electrified reports:
Cell V 4.12 (range 4.11 - 4.12)
86.9 AmpHours
85% SOH

Those last two don't seem to stack up - SOH% should be AmpHours as percentage of 94, shouldn't it?

Batt KAPPA is 26.4kW - 1kWh lower than it was just 3 months ago - so, the discharging/recharging hasn't affected that figure at all..

 

[alohart]

Electrified reports:
Cell V 4.12 (range 4.11 - 4.12)
86.9 AmpHours
85% SOH

Those last two don't seem to stack up - SOH% should be AmpHours as percentage of 94, shouldn't it?

Batt KAPPA is 26.4kW - 1kWh lower than it was just 3 months ago - so, the discharging/recharging hasn't affected that figure at all..

Your cell charge level balance seems to be good, so cell charge level imbalance can't be blamed for a reduced usable capacity.

However, the cell capacities and SOH are just calculated estimates. The mi3 app displays the minimum and maximum estimated cell capacities which would be another way to determine whether one or more weak cells exist. Does electrified display the minimums and maximums in addition to averages?

The nominal new usable capacity that BMW claims for a 94 Ah battery pack is 27.2 kWh, so your estimated current usable capacity of 26.4 kWh is 97% of the nominal new usable capacity which is great. I don't know how to determine whether your usable capacity decrease over time is real or whether the cells in your battery pack had a usable capacity that was initially above spec and is now near spec. The 120 Ah cells in the battery pack of our 2019 i3 have an estimated capacity of 125 Ah after 33k miles and a SoH of 100%, so it seems that the cells in our battery pack were above spec and haven't decreased in capacity yet. Or maybe BMW is gaming the battery capacity warranty by underrating the battery cells initially so that their capacities would have to decrease by somewhat more than 30% to trigger a battery pack replacement under warranty.

It can be frustrating when the usable capacity seems to be decreasing but there's no good way to know why or whether it's really happening. That was the situation with our 2014 i3. However, unlike with 60 Ah battery packs, there have been almost no reports of significant range degradation for 94 Ah or 120 Ah battery packs, so these later battery cells seem to be much improved over the earlier cells.

 

[MarkH]

OK. Thanks for that reply alohart.
I'm a bit confused about the relationship between:
Car displayed SOC and the electrified one
Car displayed KAPPA and the electrified SOH
A YouTube post suggests that electrified is just reading the KAPPA number from the car
Here is a screen shot of the electrified app from my car

Any clarification about these numbers would be appreciated.

Here is the previous SOH history of the KAPPA figure

 

[alohart]

I'm a bit confused about the relationship between:
Car displayed SOC and the electrified one
Car displayed KAPPA and the electrified SOH

I use mi3, so I can't be certain what electrified is displaying. I assume that both apps are displaying the same BMS data.

I believe that the SOC displayed by the apps is the absolute charge level in which 100% is the highest charge level possible if the BMS did not limit the charge level. The SOC displayed by an i3 is relative to the charge level range allowed by the BMS. For example, 100% displayed on the instrument panel is typically ~95% of the highest possible charge level that the battery cells could attain without a BMS.

A YouTube post suggests that electrified is just reading the KAPPA number from the car

I think that both are using the same BMS data. mi3 doesn't display the battery pack's maximum usable capacity in kWh (i.e., the Batt. Kapa. max value) but does display the battery pack's usable capacity in Ah. The battery pack's maximum usable capacity could be calculated by multiplying the capacity in Ah by the battery pack's voltage at full charge.

Here is a screen shot of the electrified app from my car

[img]https://photos.google.com/photo/AF1QipNChGta2HVba2modP-guZvx3nIPMSLSdYMogChd[/img]

Your screen shots aren't being displayed because their URL's aren't that of the screen shots themselves whose file extensions would be "png", "jpg", or some other image format. Google Photos apparently creates its own URL's that don't include image file extensions. I don't know whether Google Photos could create an image URL that you could use instead.

 

[MarkH]

Thanks for those clear explanations.
If I right-click on the "image" and then select "Open image in new tab", then I get to see the image.
Does that work for you(s)?

 

[EvanstonI3]

Thanks for those clear explanations.
If I right-click on the "image" and then select "Open image in new tab", then I get to see the image.
Does that work for you(s)?

No, because these images are in YOUR Google account so YOU can see them. They do not appear to be set up for sharing with anyone else. I cannot "open the image in a new tab", all I get is a 404 error.