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Discussion Starter · #1 ·
Video of behavior where rapid discharge becomes apparent at 40s:

Rapid (reported) battery disharge in low-ish temps and moderate-high power output

My 2013 Leaf @ 57k miles experiences rapid (reported) battery discharge followed by a "limited motor power" warning and sporadic drivetrain power output (which can be scary). This happens when requesting more than 40% power for more than 10-20s, in ambient temperatures of around 30°F or less. Once power is no longer requested (i.e. you stop the car), the reported remaining charge will slowly climb back to where it might have been had the rapid discharge event not taken place. This can be seen towards the end of the video.

I've taken my car to a dealer, and they said this was caused by "normal battery capacity degradation", but I disagree. The battery capacity has certainly lowered, but a lower capacity equates (in my mind) to "less range per full charge", which is very different from "99% less range when it's kind of cold, and normal range when it's slightly warmer." I'm reaching out to you all to help diagnose the issue.

The discharge rate can be as high as 2 to 3 percent PER SECOND if more than 80% power is requested. In the video I'm requesting 50% power and it drops from 50% to 36% in 17 seconds (0.82%/s). If the ambient temperature is above 40°F this does not happen at all; no significant increase in discharge rate, and no "limited motor power". For comparison, see To what degree does temperature impact EV range? | Geotab, where I should (according to their plot based on a broad range of BEVs and over 4 million trips) expect a range decrease of around 10% due to a decrease from 40°F to 30°F (very similar to the data for only Nissan Leafs here: Nissan Leaf Range: How Much Does It Lose In The Cold?). Also see https://avt.inl.gov/sites/default/files/pdf/fsev/2015LeafColdWeatherTestJune2016.pdf, a study based entirely on 2015 Nissan Leafs, where the range decreased from ~75mi to ~65mi (figure 5 on page 7) due to the same decrease in temperature. What I'm seeing is a temperature regime where my range drops from 50 or more miles to essentially 1 or 2 miles.

As you can see, my battery is at 7 "bars", so it's not a spring chicken, but I still get 50/65 miles of range in the winter/summer, which is proportionate to what you would expect based on its initial range and its reported health. Under the rapid discharge conditions shown in the video, however, the car will drop from 75% to 0% in less than two minutes.

I see this as a "failure", in that the car is nonfunctional (and dangerous, as the sporadic power output tosses the car back and forth). Further, the fact that the behavior is completely different at 30°F than at 40°F, it seems like there is something failing that causes this behavior.

Possible causes

To me, this looks like a voltage issue. As I mentioned above, after you stop the car, the reported remaining charge will slowly climb back to where it might have been had the rapid discharge event not taken place. So the charge isn't "going" anywhere; the car is erroneously reporting a lower remaining charge than what is actually in the battery.

Remaining charge is estimated using the output voltage of the battery, so for the car to report a lower remaning charge means that it thinks that the voltage from the battery is dropping dramatically. This could be one or both of two things:

1. The voltage from the battery is actually dropping FAR BEYOND even the worst expected case for battery voltage as a function of temperature, or
2. There is a sensor (perhaps a voltmeter, or a thing the voltmeter is connected to) somewhere that is, under the conditions of cold-ish and a moderate-high load, failing and providing erroneous voltage readings, causing the remaining charge estimate to lower.

I'm ambivalent to which one it is. I just want my car to not suddenly die and swerve off the road every time I go uphill in barely freezing temperatures. A new battery would be nice but unnecessary as the Leaf's current range is sufficient.

Insufficient battery voltage

The technician has already looked over the battery, and says he's confirmed that there are no leaking cells, and the car isn't reporting any diagnostic codes related to battery failure. That being the case, if it is actually the voltage from the battery that's dropping, then I'm at a loss for what the underlying cause might be given that it's not obvious to the techs.

Since this is a problem causeed by low temperature I thought about the battery heating/cooling. I know that the battery "warmer" doesn't come on until the battery temperature drops to -1°F, and then it turns off once the battery temperature has climbed back up to 14°F, and only if the reported remaining charge is > 30% (page EV-5 of owners manual https://owners.nissanusa.com/conten...sanLEAF/2013/2013-NissanLEAF-owner-manual.pdf). That doesn't seem to apply here, hence I can't think of what it might be.

Bad sensor

If the problem is a sensor or some intermediate chip between the sensor and the car computer, then I guess they could test it (in a freezer?) with a known voltage and isolate the problem.

That's all I have on it. I'd appreciate any help approaching the issue, or tips for what the technicians might do to diagnose the problem.
 

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Wow that video is a bit scary!

het yourself Leafspy, carefully get your battery down below 10%, plug in and on the voltages screen look for any cell errors at the bottom of the screen. I’m pretty sure you’ll find some. Not sure what battery warranty you have in the USA,but here the 30kwh battery (if that’s what you have?) carried and 8 year 100k mile warranty. If leafspy shows an error ask the dealer to complete a CVLI test, they will then see the error condition and initiate a warranty repair!
 

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Wow that video is a bit scary!

het yourself Leafspy, carefully get your battery down below 10%, plug in and on the voltages screen look for any cell errors at the bottom of the screen. I’m pretty sure you’ll find some. Not sure what battery warranty you have in the USA,but here the 30kwh battery (if that’s what you have?) carried and 8 year 100k mile warranty. If leafspy shows an error ask the dealer to complete a CVLI test, they will then see the error condition and initiate a warranty repair!
As it is a 2013 leaf very unlikely to be a 30 !!
Agree Leafspy is a must to help diagnose this issue.
Dont know how good Teccies are in USA but if they are like ones in UK kin useless you have to tell em what is wrong.
Im sure something like this must throw up some error codes which you will be able to see with LSpy.
Be very interested to see how it goes !
 

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I'd agree with the previous advice that you need to get an OBD port reader and LeafSpy - this will enable you to see the state of the individual cells in the battery in real time, as well as diagnostic fault codes.

At the risk of perhaps stating the obvious - it happens in cold weather because Li ion batteries are less efficient at low temperatures. The symptoms you have are not typical for a dud cell, which would always show low voltage and would be unlikely to 'regenerate' as you observed in the video. Of course, perhaps there's some really obscure and rare fault that does this, but it's probably super rare (?). Dud cells tend to stay dud.

While you may be out of warranty, this is a big safety issue for Nissan. It's not safe to lose power so rapidly while driving, and could well result in crash or injury. Nissan should be able to diagnose what the problem is - and you may see a fault code when you use Leafspy (though any competent mechanic should have seen one of these if they connected to the OBD).
 

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I'd agree with the previous advice that you need to get an OBD port reader and LeafSpy - this will enable you to see the state of the individual cells in the battery in real time, as well as diagnostic fault codes.

At the risk of perhaps stating the obvious - it happens in cold weather because Li ion batteries are less efficient at low temperatures. The symptoms you have are not typical for a dud cell, which would always show low voltage and would be unlikely to 'regenerate' as you observed in the video. Of course, perhaps there's some really obscure and rare fault that does this, but it's probably super rare (?). Dud cells tend to stay dud.

While you may be out of warranty, this is a big safety issue for Nissan. It's not safe to lose power so rapidly while driving, and could well result in crash or injury. Nissan should be able to diagnose what the problem is - and you may see a fault code when you use Leafspy (though any competent mechanic should have seen one of these if they connected to the OBD).
"Any Competent Mechanic" few and far between, if all the teccie did was the standard battery health test that they do during the annual service, then they will have not seen any error data, they need to be told to do a more in depth battery health check.

If Lspy shows that the cells are ok then something has got to be going on with the BCM.
 

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"Any Competent Mechanic" few and far between, if all the teccie did was the standard battery health test that they do during the annual service, then they will have not seen any error data, they need to be told to do a more in depth battery health check.

If Lspy shows that the cells are ok then something has got to be going on with the BCM.
'any competent mechanic' a highly subjective term ! IMO, a main dealer mechanic is unlikely to have to deal with old leafs and rare problems - so it would not surprise me at all that they've not a clue. They are probably good at washing cars, and perhaps changing fluids and filters. Complex problems on old cars - uhuh; not their strength (tho i'm sure there may be some quality mechanics there, but likely few...). Yes, any mechanic should still be able to read an error code (surely ?), but maybe the OP had the YTS job trainee on his first job :)
 

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Discussion Starter · #7 ·
Thanks all! I've got an ODB reader on the way, and I'll dig in with Leaf Spy Pro. The tech saw the video and, in response to me emphasizing the significance of the sudden power loss and how the undesired behavior is either present and debilitating or completely absent, he insisted "this is EXACTLY what a capacity problem looks like". I'm starting to feel like he's gas-lighting me.

I had been planning on driving up into the mountains at 70MPH with Leaf Spy Running to see the failure on that end, but I'll also plug in so I can see the voltage problems when charging as well. I assume this would be more evident if I connected to a 6.6kW or a 50kW DC charger rather than the 1.5kW trickle charge at home.
 

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@muxsan @Mike Schooling are both experts in degraded/upgraded/repaired Leafs. Do you think this is what a battery with low capacity behaves like?
 

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Normally a weak cell. behaviour is triggered by lower voltage limits dor individual cells whereas the rest of the logic is looking at reported capacity and a higher voltage (dragged up by the rest)

get two or three leafspy reports at say 95%, 50% and 5%.

you can run it flat on the heater over a few hours (aircon heater and windows open).

Post here and happy to advise. We don't perform repairs anymore but can recommend a couple of competent third parties.

Sent from my SM-N976B using Tapatalk
 

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Thanks all! I've got an ODB reader on the way, and I'll dig in with Leaf Spy Pro. The tech saw the video and, in response to me emphasizing the significance of the sudden power loss and how the undesired behavior is either present and debilitating or completely absent, he insisted "this is EXACTLY what a capacity problem looks like". I'm starting to feel like he's gas-lighting me.

I had been planning on driving up into the mountains at 70MPH with Leaf Spy Running to see the failure on that end, but I'll also plug in so I can see the voltage problems when charging as well. I assume this would be more evident if I connected to a 6.6kW or a 50kW DC charger rather than the 1.5kW trickle charge at home.
I think that the tech does not know what he's talking about - unless he's got a very unusual definition of 'capacity'. When the capacity in your battery drops - you can't store as many kw, and you can't go as far as the car used to. This is what happens to all Leafs. What you observe is a temporary loss of power - which seems to restore itself. If this were a true change in capacity, you'd be well outside the laws of physics as you'd be magically creating energy when it 'returned' (clue - it never left...).

I'd keep in mind that the techs in a Nissan dealership will be most familiar with ICE cars, and few (or none) will be experienced with EVs. They will mostly deal with new EVs (but wait, these hardly ever go wrong ?), not old ones, so your chance of them making a reliable diagnosis is (IMO) very low. My suggestion would be to find an EV specialist repair shop, and take along the results from LeafSpy.
 

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Discussion Starter · #11 ·
get two or three leafspy reports at say 95%, 50% and 5%.

you can run it flat on the heater over a few hours (aircon heater and windows open).
To be clear, you mean use Leaf Spy to generate a battery health report (I'll know what that is once my OBD arrives and I can play around) for three states of charge; 95%, 50%, and 5%.

When you say I can run it flat on the heater over a few hours, you mean to let the car blast the heater with Leaf Spy recording? Or do you mean to use the heater to arrive at the desired SOC in an accurate way?

I'll post here with those results, as well as some Leaf Spy data taken while I'm reproducing this issue and while charging. And my 8-year Li-ion warranty expires on April 24 this year, so if I can make a proper case this will be covered.

Thanks!
 

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@QuotientFellow I'd say with reasonable confidence the reason for the problem occurring in cold weather and at higher levels of acceleration is you have one or more high resistance cells. This is a separate condition to capacity degradation - although both can and sometimes do occur together in the same cell.

All cells have higher resistance when cold (especially below 0C) however if the cell resistance is already abnormally high (but still tolerable) in warm weather, when the cells are cold the cell resistance will be excessively high and out of the normal tolerable range that the BMS is expecting.

Higher cell internal resistance means the voltage of the cell drops lower under load for the same load current and state of charge of the cell. If the voltage of any individual cell drops below a pre-set threshold - probably around 3.0 volts, the car will report a problem or go into turtle mode or start re-evaluating the remaining charge available even if all the other cells are at a normal voltage.

I have some first hand experience of this kind of problem in my previous Peugeot Ion where I had a group of 4 cells that developed faults over time - two of them just lost a lot of capacity relative to the rest of the pack but the other two lost capacity and developed abnormally high internal resistance.

The most obvious symptom of the higher internal cell resistance is neutered rapid charging speeds even in warm weather - and this is actually why I first noticed it and how I ultimately diagnosed high internal resistance. This is because during rapid charging the maximum cell voltage (4.1v on the Ion) cannot be exceeded for any individual cell - if a cell has high internal resistance the voltage will go higher than other cells and quite quickly as a result rapid charging is throttled at an unusually low SoC. For example I was seeing the two high resistance cells hit 4.105 volts at the same time other cells were only at 4.075 volts, which is a huge difference in potential charging speed during rapid charging.

Conversely if you're driving at a lower SoC then hit the accelerator and the voltage of the high resistance cell buckles and goes below the minimum allowable cell voltage the BMS will freak out in a big way. On the Ion it instantly put the turtle mode indicator on and limited power, then as soon as you lifted the accelerator it went back to normal when the voltage rebounded.

On the Leaf it apparently behaves a little bit differently when faced by abnormally low cell voltage under load, but I think the sudden drop in reported SoC before your very eyes is a result of one or more cells suddenly (during heavy load) reporting low voltage and causing the BMS to rapidly re-evaluate the available SoC.

We have seen this sort of behaviour reported for Leaf's before - not as dramatically as this, but people with individual faulty cells have reported that the last 20-30% goes down very very rapidly. This will be for a similar reason that some cells are reaching an abnormally low voltage for the SoC the BMS believes the pack is at.

As to how to diagnose the problem - Leaf spy and a helper to drive the car while you study the measurements should be all you need.

First check the reported SoH (which is going to be pretty darn low with 7 bars!!) and check the voltage balance between cells when the car is fully charged to see whether it is balanced or not.

Then drive the car until SoC is down at the point where the problem is occurring, and take a note of the cell voltage imbalance while the car is on but stopped (and which if any cells are imbalanced) then on a quiet uphill road have your driver progressively apply more power to see whether the imbalance worsens, and most importantly, what voltage is the lowest cell reporting when the acceleration is just high enough to trigger the problem.

The third test I would do is a rapid charging test, start with the car at say 40% SoC, take a note of the cell voltage balance between cells while the car is on not being driven as a baseline, then plug the car into a rapid charger and see what happens to the voltage vs the car just turned on not charging.

All cell voltages will of course increase significantly and immediately during charging but if you see any particular cells suddenly go to a much higher voltage than the others and they weren't just before rapid charging those cells have high internal resistance, since high internal resistance causes excessive voltage rise during charging. You're looking for cells whose voltage increase significantly more than others when rapid charging starts.

Actually measuring cell internal resistance directly on a cell out of the car needs fairly specialist equipment, (as the test current needed is very high and the resistance is only a milliohm or so) and there is no useful information available in the Leaf BMS to provide this info (at least not available with Leafspy) however the rapid charge voltage increase test is a good proxy for cell resistance and a more stable and easy test to perform than a discharge test while driving at a constant acceleration.

As to whether the behaviour you're seeing is "normal degradation" - absolutely not. If you can't use full acceleration even at low SoC then there is definitely a fault or the cells are excessively degraded to the point where any remaining warranty should be covering them.
 

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Discussion Starter · #13 ·
Thank you @DBMandrake for your detailed analysis and suggestions! I had a couple questions.

I've crossposted on mynissanleaf as well where the discussion has turned vibrant: [help] Rapid battery discharge, "limited motor power", and sporadic power output at temp. < 30F and > 40% motor power. - My Nissan Leaf Forum

@QuotientFellowThe most obvious symptom of the higher internal cell resistance is neutered rapid charging speeds even in warm weather - and this is actually why I first noticed it and how I ultimately diagnosed high internal resistance. This is because during rapid charging the maximum cell voltage (4.1v on the Ion) cannot be exceeded for any individual cell - if a cell has high internal resistance the voltage will go higher than other cells and quite quickly as a result rapid charging is throttled at an unusually low SoC. For example I was seeing the two high resistance cells hit 4.105 volts at the same time other cells were only at 4.075 volts, which is a huge difference in potential charging speed during rapid charging.
This sounds like what I experienced the one time I did a full DC recharge from about 12% to 90% SOC on a 50kW ChargePoint charger. I expected it to hum along at close to 50kW (or whatever the max supported by my 24kWh Leaf) until it got to around 80%, then decrease the power logarithmically-ish until it trickled to full. Instead, it rose to about 35kW for a minute or so, and immediately started the logarithmic-ish throttling as shown below:
139718


Contrast this to when I charge at 6.6kW (from aobut 30% to full) and it follows my expectations:
139719


So this adds to the growing set of evidence that my issue is caused by one or more bad cells. Can't wait to get at this with Leaf Spy Pro.

I've noticed that the car always charges in about 60% of its estimated time. That's also explained by the bad cells' reduced capacity; they fill first spike voltage once full, making the car think it's at full SOC.

@QuotientFellowThen drive the car until SoC is down at the point where the problem is occurring...
I just wanted to reiterate that this only happens at below around 30°F ambient. I should expect that with Leaf Spy this would be evident at higher temperatures as well, but the behavior in the OP video hasn't yet occurred at higher than 32°F (under similar load up same hills at same speed).
 

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I just wanted to reiterate that this only happens at below around 30°F ambient. I should expect that with Leaf Spy this would be evident at higher temperatures as well, but the behavior in the OP video hasn't yet occurred at higher than 32°F (under similar load up same hills at same speed).
[/QUOTE]
When you start using LeafSpy, you'll see that it gives the exact battery temperature. While your issue occurs 'around freezing' the battery temperature will diverge from ambient based upon use and charging. Thus, you should be able to get a much more exact measure of the battery temperature at which the problem occurs using Leafspy (though i suspect it's the cell data that will illustrate what the problem is !)
 

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This sounds like what I experienced the one time I did a full DC recharge from about 12% to 90% SOC on a 50kW ChargePoint charger. I expected it to hum along at close to 50kW (or whatever the max supported by my 24kWh Leaf) until it got to around 80%, then decrease the power logarithmically-ish until it trickled to full. Instead, it rose to about 35kW for a minute or so, and immediately started the logarithmic-ish throttling as shown below:
View attachment 139718

Contrast this to when I charge at 6.6kW (from aobut 30% to full) and it follows my expectations:
View attachment 139719

So this adds to the growing set of evidence that my issue is caused by one or more bad cells. Can't wait to get at this with Leaf Spy Pro.
I wouldn't jump to that conclusion just yet - the 24kWh Leaf has a much earlier rapid charge taper than the 30kWh model. Have a look at the graph on this page and see how it compares to your car:


You can see the 24kWh model actually starts to taper gradually at around 25% although it should stay above 30kW until about 60%. On the other hand the 30kWh model maintains full charge speed right until 80%.

The graph above will be based on warm cells that are between 20-40C, at very cold temperatures internal resistance goes up and charge rates will be tapered back sooner, also the maximum charge rate will be limited below some temperature to avoid Lithium plating of the graphite electrode.
 

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Discussion Starter · #16 ·
Ah I see, the 24kWh curve in the plot does look more like my DC charging plot than it does any of the larger capacity battery curves. And I assume that's for healthy (i.e. 12 bars) batteries. As you point out, by comparison mine lowers to below 30kW sooner than their plot, but it does seem qualitatively the same. Thanks!
 

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@QuotientFellow did you ever manage to get a LeafSpy report from your car and work out what is going on with it?

Im very curious to find out what has actually caused this strange behaviour!
 

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Discussion Starter · #18 ·
I have the car and LeafSpy in hand. I believe I've identified the bad cells, but it's not as drastic as expected. Under the conditions in the video, the voltage difference between cells gets as high as 800mV, with the low voltage cell at 2V. I had thought this would be enough to trigger a DTC, but I guess not.

Meanwhile, under smaller loads, the cell voltages are very close, with a max difference of usually less than 40mV.

The max cell voltage difference when quick-charging (max charging rate of ~28kW) was likewise around 40mV.

I've some cold weather coming next weekend. I intend on performing some stress-testing to see if I can't get some DTCs to appear.
 

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I have the car and LeafSpy in hand. I believe I've identified the bad cells, but it's not as drastic as expected. Under the conditions in the video, the voltage difference between cells gets as high as 800mV, with the low voltage cell at 2V. I had thought this would be enough to trigger a DTC, but I guess not.

Meanwhile, under smaller loads, the cell voltages are very close, with a max difference of usually less than 40mV.

The max cell voltage difference when quick-charging (max charging rate of ~28kW) was likewise around 40mV.

I've some cold weather coming next weekend. I intend on performing some stress-testing to see if I can't get some DTCs to appear.
How many low cells have you identified / do you have a LeafSpy screenshot?

Have you tried running it down to a low SOC?

I.E. less than 10% and then trying a full acceleration run?

If you have a very bad cell this is likely to strand you so I’d suggest trying this in a safe place heading towards a very close by charge point.

This is most likely to trigger the codes needed to get a free CVLI test.

Your car must be very close to it’s 8 year battery warranty expiring so it would be good to get this fault to throw prior to that.
 

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What does this screen show at low state of charge? I am expecting to see the "Bad Cells" message at the bottom of the screen. If it is, then a CVLI test at the dealer will tell them to service the battery even without a DTC.
 
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