battery degradation after 3 years

[psquare]

We've had our Rex for almost 3 years now (40,000 miles) and I've done the "battery capacity max" check in the System Menu for the first time. It read 16.9 kWh, which is down 2.5 kWh from the original 19.4 kWh. The car is currently with my BW dealership for MOT and a end-of-warranty check.

I am obviously aware of the 8year/100,000 mi warranty on the battery itself.

Has anybody else noticed similar degradations?

Thanks.

 

[Benagami]

I'm told that battery kappa varies depending on temperature. I too have a 2014 i3. Mine has 22,000 miles. Last time I measured kappa it was 19.2. That was when it was 70 degrees F out.

 

[psquare]

I'm told that battery kappa varies depending on temperature. I too have a 2014 i3. Mine has 22,000 miles. Last time I measured kappa it was 19.2. That was when it was 70 degrees F out.

I've noticed that the max mileage displayed used to be 65mi when 100% in cold UK winter conditions (0 - 2 deg C, preconditioned). These days it is more like 58-60mi in the morning under the same circumstances.

Before people respond that it depends on the last 18mi of driving style... I know all that! Our driving styles haven't changed significantly.

Battery degradation is a fact of EV life. I just want to establish whether this kind of wear, which appears to be in line with the warranty offer by BMW (8yrs/100k mi), is also in line with other i3 owners.

 

[john41]

3 year old 2014 i3 Rex with 26k miles on it here. Max kappa has also been between 16.6 kwh and 17 kwh over the past few weeks, showing 16.9 kWh most of the time. The range has also decreased accordingly.

The biggest drop in max kappa happened around the time bmw updated the BMS software to fix the issue where the Rex was sometimes going on too late for people with older batteries, leaving them stranded. The capacity has kept drecreasing since though.

I’ve heard somewhere that BMW can calibrate the BMS by emptying the battery in a controlled way and measuring the output. I may ask them if they can indeed do that if things keep getting worse. It’s unclear at this point whether this is real degradation, or badly calibrated BMS software...

 

[alohart]

The stated usable capacity of the 60 Ah battery pack is 18.8, not 19.4 kWh. With the 30% capacity degradation limit in the U.S. battery pack warranty, the usable capacity would need to be less than 18.8 * 0.7 = 13.2 kWh for a warranty claim to be made. Batt. Kapa. max on our 2014 i3 BEV have varied from 16.5 to 20.9 kWh with the higher values being more recent which makes no sense.

A one-time Batt. Kapa. max reading isn't of much value. It's a calculated, not directly measured value, but we don't know how Batt. Kapa. max is calculated.

When the July, 2016, system software was installed on our i3, Batt. Kapa. max values suddenly increased to the 19-21 kWh range, so the software version likely affects Batt. Kapa. max values.

I don't pay as much attention to Batt. Kapa. max values as to actual driving range, not range estimates.