Charting Battery Capacity/ State of Health Over Multiple Years

[3pete]

I assume that you wrote BimmerLink's description of DTC 21F137. If so, that doesn't make much sense with an 80% SOH.

The BMW fault code Website lists a variety of descriptions for DTC 21F137 depending on the SME version. On an ISTA report for our 2021 i3, the SME version is SME_I1 which isn't listed under DTC 21F137. Maybe your i3 has a different SME version and 21F137 isn't a DTC for SME_I1. Or maybe the BMW fault code Website is missing the i3 description for DTC 21F137. I hope that ISTA would provide a better description for DTC 21F137 on an i3.

Correct-- that's the description BimmerLink gives, which I found interesting. If the description is to be believed, it makes me think there is yet another way to measure capacity that yields a result different than the 4+ I've been tracking.

 

[Marscar]

Howdy all!

It's been a while since I've posted in this thread, partially because the i3 has been relegated to second car status in the household, so I've been driving it a LOT less.

Recently I've had chances to log enough additional data points that an update is possibly meaningful.

My notes/observations are:
1) Method/Graph #4 seems to be the most reliable way to measure capacity. The variability in that graph is high, but unlike the others there isn't an obvious disruption in the trend when something like a software change happens (vertical dashed line)

2) I am more confident now that charging behavior impacts Batt Kapa Max values significantly. My i3 switched from primary car around 75k miles, at which point I started leaving it not-fully-charged since I may not drive it for days or weeks. Instead, I charge it up the day I know I'm going to use it and it's not always to 100% by the time I leave.

Compare that to the 45k and 75k segment on the graph where it basically got daily use and was charged on an L2 charger to 100% whenever I got home.

3) The Electrified app is currently showing SOH at 80%

4) I recently scanned error codes using BimmerLink and got one in the BME that I can't find documented well on the internet: "21F137: HVS: Battery aging: SOH low (warning threshold)". I may create another thread specific to that considering this thread is long already.

Hi.
Could you unpick point 2 for me?
Which "behaviour" is best, based on your data?
Our approach with a 2018 33kwh i3 REX that we bought in, I think, 2022 has been almost entirely 3 pin charging at home on a dedicated circuit, always charging overnight on cheap rate, to the "100%" and not using for a few hours after the "charging complete" time. (so 'departure time" always about three hours after the expected finish)
We also rarely go below "70%" in order to charge to "100%" within 5 hours ......?

 

[3pete]

Hi.
Could you unpick point 2 for me?
Which "behaviour" is best, based on your data?
Our approach with a 2018 33kwh i3 REX that we bought in, I think, 2022 has been almost entirely 3 pin charging at home on a dedicated circuit, always charging overnight on cheap rate, to the "100%" and not using for a few hours after the "charging complete" time. (so 'departure time" always about three hours after the expected finish)
We also rarely go below "70%" in order to charge to "100%" within 5 hours ......?

I should clarify that my theory is: charging to less than 100% yields a wider variance in batt Kapa max values. So if you're trying to do anything with batt kapa max readings the charge behavior might matter. Basically, reinforcing that when people post a single batt kapa max value and ask what it means, the answer is either "it depends" or "basically nothing."

In my experience, charging from something below 50% to 100% on L2 every night seems to yield the most consistent values. Whether those values are more accurate or useful is a different question.

Despite what this thread may suggest, I also believe it's not really worth stressing too much about degradation. If there's a charge behavior that works best for you, that's what I would recommend.