The 40KWH Battery Topic

[jdcbomb]

Why did the Hx value in my 40 kWh start off in the mid 90's and now with a SOH of 95.70 the Hx is around 113. Is there any technical reason?

[DaveinOlyWA]

Why did the Hx value in my 40 kWh start off in the mid 90's and now with a SOH of 95.70 the Hx is around 113. Is there any technical reason?

Yes there is a technical reason but specifics can only be supposed.

I "think" the change in chemistry and resulting change in resistance values has caused the higher than normal reading. My Hx has been between 118-119 for months now.

[lorenfb]

Why did the Hx value in my 40 kWh start off in the mid 90's and now with a SOH of 95.70 the Hx is around 113. Is there any technical reason?

Yes there is a technical reason but specifics can only be supposed.

I "think" the change in chemistry and resulting change in resistance values has caused the higher than normal reading. My Hx has been between 118-119 for months now.

Nissan most likely didn't modify the algorithm that calculated Hx (the ratio of the battery's conductances - present/initial) based
on the later batteries, e.g. using the older batteries' initial conductance value which would cause Hx to be greater than 100%.

[goldbrick]

Why did the Hx value in my 40 kWh start off in the mid 90's and now with a SOH of 95.70 the Hx is around 113. Is there any technical reason?

Yes there is a technical reason but specifics can only be supposed.

I "think" the change in chemistry and resulting change in resistance values has caused the higher than normal reading. My Hx has been between 118-119 for months now.

Nissan most likely didn't modify the algorithm that calculated Hx (the ratio of the battery's conductances - present/initial) based
on the later batteries, e.g. using the older batteries' initial conductance value which would cause Hx to be greater than 100%.

Are you sure that is the algorithm used to calculate Hx? I find it hard to imagine that while reprogramming the BMS for the new models that the value of the initial conductance (a constant) wasn't changed. As far as I know, no one here really knows what Hx means. Like the old adage "those that know don't say and those that say don't know". It will be interesting to see what happens to Hx values as the 40kWh and 60kWh packs age but practically speaking, what difference does it make? Does it affect charge rate, regen rate, or anything meaningful at all?

[lorenfb]

Nissan most likely didn't modify the algorithm that calculated Hx (the ratio of the battery's conductances - present/initial) based
on the later batteries, e.g. using the older batteries' initial conductance value which would cause Hx to be greater than 100%.

Are you sure that is the algorithm used to calculate Hx?

1. It appears to be a percentage, e.g. 0 - 100%.
2. It tracks SOH, i.e. declines as the battery ages.
3. It does agree with the inverse of the ratio of the battery resistance over time.
4. It provides additional insight into battery degradation over time.

My 2013 battery resistance over time:

12/27/14 - 14,800 miles, 103 mohms per LeafDD, 11 deg, 24% SOC
3/10 - 17,400 miles, 60 mohms per LeafDD, 30 deg, 73% SOC
3/14 - 17, 550 miles, 56 mohms per LeafDD, 32 deg, 47% SOC
4/14 - 19,100 miles, 59 mohms per LeafDD, 25 deg. 38% SOC
5/4 - 19,989 miles, 64 mohms per LeafDD, 24 deg. 48% SOC
5/15 - 20,400 miles, 73 mohms per LeafDD, 20 deg. 41% SOC
5/22 - 20,700 miles, 58 mohms per LeafDD, 28 deg. 50% SOC
12/10/15 - 28,000 miles, 90 mohms per LeafDD, 19 deg. 92% SOC
4/5 - 32,000 miles, 74 mohms per LeafDD, 24 deg, 55% SOC
5/16 - 33,700 miles, 89 mohms per LeafDD, 22 deg, 47% SOC
5/16 - 33.700 miles, 58 mohms per LeafDD, 31 deg, 76% SOC
10/5 - 39,300 miles, 100 mohms per LeafDD, 22 deg, 50% SOC
10/6 - 39,400 miles, 61 mohms per LeafDD, 30 deg, 51% SOC
10/7 - 39,500 miles, 80 mohms per LeafDD, 25 deg, 56% SOC
10/15 - 40,000 miles, 71 mohms per LeafDD, 27 deg, 45% SOC
10/30 - 41,000 miles, 74 mohms per LeafDD, 23 deg, 66% SOC
12/26/16 - 43,000 miles, 110 mohms per LeafDD, 13 deg, 77% SOC
6/10/17 - 49,600 miles, 89 mohms per LeafDD, 19 deg, 70% SOC
7/1/17 - 51,000 miles, 62 mohms per LeafDD, 33 deg, 44% SOC
8/15/17 - 53,400 miles, 61 mohms per LeafDD, 35 deg, 57% SOC
4/2/18 - 62,100 miles, 110 mohms per LeafDD, 18 deg, 94% SOC
6/13/18 - 65,000 miles, 84 mohms per LeafDD, 26 deg, 52% SOC
8/13/18 - 67,000 miles, 80 mohms per LeafDD, 26 deg, 91% SOC
9/14/18 - 68,000 miles, 84 mohms per LeafDD, 27 deg, 57% SOC

And you have a better assumption?

[EnigmaEV]

After 15 months of regular, fairly consistent decreases in SOH, LeafSpy has reported my first INCREASE in SOH. I started out at 93.95% on July 5th and ended the day at 94.09%. Yesterday it dropped the regular 0.01% to 94.08%. There was nothing significantly different about the driving or charging I did on the 5th - 49 km driven, pack temperature 20-22C, SOC near 50%, no charging. We don't have any L3 chargers within 500 km so I have never rapid charged it. It gets charged to 100% twice a week just prior to a 100 km trip.

Has anyone else seen an increase in SOH with a 40 kWh pack? I know it was common with 24 and 30 kWh packs, particularly after a rapid charge, but I have not read/heard about any 40 kWh packs that have shown an increase in SOH.

Degradation seems to have slowed significantly as the pack has aged. SOH dropped from 99.57% to 94.84% (4.73%) in the first 6 months with 12,000 km (7,500 mi) driven. In the 9 months since (includes 6 months of winter) I have driven 16,000 km (10,000 mi) with SOH only dropping from 94.84% to 94.08% (0.76%). If this trend continues, the longevity of the 40 kWh pack might be pretty good - at least in a cool/cold climate - and if you can trust the data provided by the BMS.

[LeftieBiker]

I haven't seen an increase, and haven't read of one before yours. My own experience was a disturbing drop in SOH the first 6 months, then virtually no drop over the first Winter and Spring, resulting in a first year drop of about 4.6%, IIRC. I haven't checked it this Summer.

[SageBrush]

I haven't checked it this Summer.

A tried and true method to stop LEAF battery degradation.

[LeftieBiker]

A little less snark would be appreciated. I decided after the last reading that 6 month intervals would be sufficient.

[DaveinOlyWA]

SOH rise is unique. I have seen a single "point" (.01%) rise during the day that negated itself by the next morning (only record data in morning or before first drive of the day)

As far as my loss, its settled into a pattern of a relatively large chunk lost every 90 days. Because of this rather predictable pattern, I have varied both charging and driving habits to see if anything affected this 90 day cycle and nothing has so far.

I am a few days to maybe a week to my next "adjustment" so we shall see what happens.