Two cars, three battery packs, all sudden SoC drops

[Jerther]

I don't believe this. I thought those days were over.

My previous 2018 40 kWh went through two successful battery pack warranty claims because of sudden SoC drops. ( #1, #2 ) I never got to test the third battery because I sold the car and bought the 2022 63 kWh I have now. So I got up this morning, it was -7 C outside. Car was at 54% SoC. Drove to work, and then on the dreaded hill on the highway where it always occurred on the 2018, the SoC went from 36 % to 29 % in 2 seconds, then slowly back up again as I got up the hill.

Really???? I mean, AGAIN!?!?!?

Now that's two cars, three battery packs. What's wrong with me Is this normal and my dealer is being too nice!?!?!?

I'll use Leaf Spy to watch for low peaks in the battery pack next time this occurs... :'(

 

[Stanton]

While the symptoms are similar...it may not be a "failure" this time. -7 degrees (anything) is pretty cold, and it's well known that Lithium cells stress under low temps. At least you have a good "test incline" on the way to work...

 

[cornbinder89]

-7c is about 19.5 deg F, not what I'd consider cold. -10F is what I would consider cold enough to see problems, but in might be different in the plus as I don't believe those have battery heaters? I stand to be corrected on that point.
-7 c I'd expect to see a fair drop in overall range, but not a huge drop under load.

 

[Jerther]

-7 C is just the beginning. We often get -15 C for days, sometimes weeks in the dead of winter here.

I believe LEAFs sold in Canada all come with a battery pack heater installed. In any case, the battery heater won't kick in unless the temperature drops way down below -10 C. I'll have to check the owner manual again, but I think it's like -20 C. If I could raise that temperature bar to 0C, or have it turn on an hour before I leave, I certainly would, and from experience it would most certainly fix that behavior.

 

[Drew21]

Does your car sit outside at night? Is it driven every day or does it have time for the battery to fully drop to ambient temperature? What type of speed and slope are we talking about for your hill of despair? Do you try to accelerate up the hill or is the speed constant?

It's possible that you're asking a very cold battery to provide maximum go and it stumbles in that specific condition.

 

[Jerther]

It sits ouside. It's coated with a layer of hard snow and ice right now. It is driven pretty much every day these days, two times a day. From previous measurements, the battery does not have time to fully cool. I'll have to take new measurements for the 63 kWh. On the hill of despair (love that), it's usually 110 km/h to follow traffic, using cruise control to keep the speed stable. At this speed, the slope pushes the LEAF to about 50 or 60% power for about a minute.

The hill is about 30 km away from home. The battery has some time to warm up, but I remember from my 2018 40 kWh in very cold -15 C days that 30 km is not enough to get it to cross 0 C.

My question is: if this is normal, then what's different this time compared to the two successful warranty claims I had for the same problem? I mean the "problem" could be different this time but the behavior is the same, and I guess my goal now is to gather enough information to tell the difference, if there's any. So next time, it's leaf spy screenshot and battery pack temperature.

The best way around this for me would be to rent a brand new leaf, a demo perhaps, and see if I get the same thing. But I asked my dealer and they can't...

 

[Drew21]

I don't know enough about operating a Leaf in very cold conditions to offer quantitative advice, but the conditions you describe match up well with what others (e.g., cornbinder) have reported as being the point where even a "good" battery can start to struggle. I don't know if that means that it's "normal," but based on what I've read here since getting a Leaf a few years ago I don't think its abnormal.

We know that cold Li-ion batteries have a reduced ability to push electrons. Doesn't matter if you're talking EVs, laptops, cellphones, or cordless tools. Add to that the slope and speed of your hill which require 50-60% load per your description. So, the cold battery hiccups a bit, the BMS sees the rapid voltage drop (maybe in a few weaker cells or maybe across the battery), and you see the SoC/range drop precipitously.

Once you change the conditions (warmer temperature or reduced load) the battery voltage stabilizes and the SoC/range estimate pops back up to (roughly) where it was before the episode.

It would seem that no battery has perfectly balanced cells, especially as the battery gets older. Some driving conditions -- very low or high temperatures, high speed, steep/long slopes -- will tend to accentuate even minor cell/battery issues. Other driving conditions -- generally mild temperatures, garage (even unheated) parking, lower speed, gentle terrain -- will tend to mask cell/battery issues such that the ignorant, non-LeafSpy driver (i.e., me) doesn't even know if what they don't know is hurting them.

 

[Jerther]

I'm aware that I'm overly aware of the car, specifically of its traction battery Primarily because of the first warranty claim where the battery was just done. It would suddenly drop tens of points of SoC even at 95%. The first time it occurred (on Hill of Despair) it scared the *** out of me.

 

[tractioninc]

We are

I'm aware that I'm overly aware of the car, specifically of its traction battery Primarily because of the first warranty claim where the battery was just done. It would suddenly drop tens of points of SoC even at 95%. The first time it occurred (on Hill of Despair) it scared the *** out of me.

Scared the crap out of me when it started happening. Our Leaf belongs to my daughter, a new driver, and the prospect of getting stranded out on the highway has her afraid to drive it.

 

[Jerther]

@tractioninc since you appear to have four EVs, does this only occur on the LEAF? Or other EVs do this too?

 

[tractioninc]

No, we've never experienced sudden estimated range loss in the other cars, even the first-gen Leaf. There was real moment of panic for my daughter and I when it happened the first time!

 

[Frankshay]

New to Leafs but not EV's...

I'm sure you know that in cold weather you're always best served to start with a higher SOC but I suspect it's totally normal to see that kind of drop under load. You hit your "hill of despair" with about 20 kWh capacity remaining in the pack so the instantaneous current draw was a large percentage of remaining amp-hours. The calculation showed SOC going back up because current draw dropped back.

 

[Jerther]

New to Leafs but not EV's...

I'm sure you know that in cold weather you're always best served to start with a higher SOC but I suspect it's totally normal to see that kind of drop under load. You hit your "hill of despair" with about 20 kWh capacity remaining in the pack so the instantaneous current draw was a large percentage of remaining amp-hours. The calculation showed SOC going back up because current draw dropped back.

Yep that all made sens since the first time it happened to me. I'm just not convinced suddenly getting stranded with an almost new car with seemingly lots of range left just because it's cold is intended behavior for a consumer product targetted at the average driver who does not know much. If this was well known and normal, I would bet my paycheck that nobody here would drive EVs. I mean, limited range is on everyone's lips, but sudden drops like these would deter pretty much any potential buyer. I for one would have backed off two years ago when I didn't now any better.

That being said, I have had two leafs, and love them enough to keep them and learn to live with their actually intended limits

 

[MasterFlier]

I'm getting the same thing on my 2020 SV. It makes sense to me that the calculated range would rise when going from hard load to light load, but why would the percent SOC rise under light load? I guess I think in ICE terms, that the amount of battery left is like the amount of gasoline left in an ICE, and once you've used some of it it doesn't come back if you let off the accelerator.

 

[Jerther]

Our understanding is that the car reports it's soc based in the cell with the least voltage among the ~95 in the pack. Batteries (alkaline, lithium, nicad, NiMH...) voltage drop curve when discharging is not linear and it suddenly drops when it's almost depleted, and every battery is different, even in the same pack, but I think they should be similar. It's just that in the leaf, it looks like there's often (always?) one or a few cells that has its voltage drop a LOT sooner than the others, and the cars goes crazy about it.

 

[Jerther]

And to answer your question, the soc rises back because the voltage drop is caused by a heavy load on the battery. Remove the load, and the voltage comes back up. The more load you put on a battery, the more it's voltage drops and it eventually starts to collapse when it's nearing depletion.

The battery management system on the leaf tries to mitigate all that for almost a hundred cells, and report a linear SoC in % for the entire pack. I recon it is quite a feat, but apparently it has its flaws.

 

[hornstudio]

Same happened to me in July 2023, two months before 5 year warranty was over. I brought it to Nissan battery center and after they replaced some cell blocks the SOC was still jumping around under load.
I complained and said there was probably a BMS update missing like "SOC should react way slower like an ICE would do"? Nissan said to bring the car back in again.
I sold the car to a buyer who wanted this car so bad, he took a test drive, saw the jumping SOC and the buyer wanted to follow up on this issue with a friend, also Nissan dealer.
He missed to do the 5 year warranty service at his Nissan friend and brought the car back to a Nissan battery center who then replaced the BMS unit, at least for free. Nissan battery center missed to do a highway probe drive.
So he got the car back, SOC still jumping around. The guy went mad, he was asking for 2 more cells to be replaced by Nissan. Nissan refused warranty, they said "he missed the 5 year service".
Owning the car since a year now, he took a lawyer and put me to court as "the seller". I am curious.