Rapid battery discharge, "limited motor power", and sporadic power output at temp. < 30F and > 40% motor power.

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FurryRutabaga
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Rapid battery discharge, "limited motor power", and sporadic power output at temp. < 30F and > 40% motor power.

Postby FurryRutabaga » Sat Jan 16, 2021 10:30 am

Video of behavior where rapid discharge becomes apparent at 40s:
https://youtu.be/dULaMW2cUXQ

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 https://www.geotab.com/blog/ev-range/, 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: https://www.greencarreports.com/news/10 ... n-the-cold). Also see https://avt.inl.gov/sites/default/files ... ne2016.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/content/te ... 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've ordered an ODB sensor and I'll dig in with Leaf Spy Pro to identify the bad cell(s), if that's the problem, by observing individual cell voltages when driving and when charging.

Beyond that, thanks in advance for any help approaching the issue, or tips for what the technicians might do to diagnose the problem.


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VStar650CL
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Re: Rapid battery discharge, "limited motor power", and sporadic power output at temp. < 30F and > 40% motor power.

Postby VStar650CL » Sat Jan 16, 2021 10:46 am

Your problem is current delivery and not voltage, and yes, when a Li-ion battery is severely depleted at the end of its life, its ability to deliver maximum current under load suffers greatly. The dealership wasn't lying, your battery is simply shot and the car is doing its best to keep running anyway.

FurryRutabaga
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Re: Rapid battery discharge, "limited motor power", and sporadic power output at temp. < 30F and > 40% motor power.

Postby FurryRutabaga » Sat Jan 16, 2021 3:41 pm

VStar650CL wrote:
Sat Jan 16, 2021 10:46 am
Your problem is current delivery and not voltage, and yes, when a Li-ion battery is severely depleted at the end of its life, its ability to deliver maximum current under load suffers greatly. The dealership wasn't lying, your battery is simply shot and the car is doing its best to keep running anyway.
So every Leaf at 7 bars is expected to lose power and go into turtle mode under moderate load at 30°F, but not any problems whatsoever at 40°F?

I can't find anything about this type of low-ish temperature behavior being expected for li-ion batteries, either in the specific application of EVs or in the scientific literature where the same battery technology is tested under all feasible conditions and at every point in its life span. Whatever the observed effects of temperature are on power delivery for aging batteries, it is still continuous with respect to temperature. What I'm experiencing is a discontinuous relationship, where the undesired behavior goes from not present to complete failure as a result of a 10°F difference, nothing like what's observed for li-ion batteries.

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VStar650CL
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Re: Rapid battery discharge, "limited motor power", and sporadic power output at temp. < 30F and > 40% motor power.

Postby VStar650CL » Sat Jan 16, 2021 6:34 pm

All batteries deliver less current at low temperature. That's basic chemistry, cold slows down reactions. Your situation is an exact analog of a 500 CCA 12V battery that has depleted to 300 CCA and worked fine all summer but won't start the car on a winter day. Sorry to say, it's shot.

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Re: Rapid battery discharge, "limited motor power", and sporadic power output at temp. < 30F and > 40% motor power.

Postby Rogue One » Sat Jan 16, 2021 7:10 pm

2013 Nissan LEAF | Warranty Information Booklet | Nissan USA
The Lithium-Ion coverage period is 96 months or 100,000 miles, whichever comes first.
One of the most important rules of Nissan LEAF battery maintenance is keeping the battery charge between 20% and 80%. Letting your LEAF’s battery die regularly or charging it to full capacity regularly will cause your battery modules to degrade faster.

Your LEAF’s battery health can be directly affected by extreme temperature fluctuations. When possible, try to avoid leaving your LEAF in the hot sun for too long, as it can add a substantial amount of stress on the battery pack and shorten its life due to things like lithium plating and thermal runaway.

While cold temperatures don’t directly affect lithium-ion degradation, they can shorten your LEAF’s range due to the electrolyte fluid in the battery pack moving at a slower pace or freezing. Additionally, the cold can limit the amount of energy your LEAF is supposed to recoup during regenerative braking.

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VStar650CL
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Re: Rapid battery discharge, "limited motor power", and sporadic power output at temp. < 30F and > 40% motor power.

Postby VStar650CL » Sat Jan 16, 2021 7:19 pm

Rogue One wrote:
Sat Jan 16, 2021 7:10 pm
The Lithium-Ion coverage period is 96 months or 100,000 miles, whichever comes first.
That's for the battery hardware, depletion has a special warranty that will be expired on a '13. However, due to the low miles, there's a good chance the dealer can get Nissan to help out with a "goodwill" repair where Nissan picks up part of the cost of a new battery and/or labor.

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Re: Rapid battery discharge, "limited motor power", and sporadic power output at temp. < 30F and > 40% motor power.

Postby Rogue One » Sat Jan 16, 2021 7:29 pm

Thanks for the clarification! :dblthumb:

FurryRutabaga
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Re: Rapid battery discharge, "limited motor power", and sporadic power output at temp. < 30F and > 40% motor power.

Postby FurryRutabaga » Sun Jan 17, 2021 11:04 am

VStar650CL wrote:
Sat Jan 16, 2021 6:34 pm
All batteries deliver less current at low temperature. That's basic chemistry, cold slows down reactions. Your situation is an exact analog of a 500 CCA 12V battery that has depleted to 300 CCA and worked fine all summer but won't start the car on a winter day. Sorry to say, it's shot.
Lower uniform capacity only affects range; you don't expect to not be able to drive up a hill because of decreased capacity. Your analogy of a 12v battery not being able to start the car is fine, and applicable here, in that the battery isn't able to provide the high requested voltage (and current). But clearly, an EV battery is more complicated, composed of far more cells, and equipped with more sensors and process control systems that are measuring individual cell voltages than a 12v car battery.

In my case, there are one or more bad cells whose capacity has dropped far more than the rest of the "normal" cells in the battery. It's not the entire battery that cannot provide the necessary voltage at 50% throttle; it's just one or more bad cells, and because the battery management system (rightly) uses the lowest cell voltage as the indicator of available voltage from the whole pack, it sees that the voltage is too low and turns on turtle mode to accommodate.

The 5-year warranty pertains to uniform capacity lowering in an otherwise heathy pack, resulting in decreased range coupled with otherwise normal driving performance, i.e. you should still be able to drive up a hill. What I'm experiencing is the result of bad cells that have degraded disproportionately more than the healthy cells, which not only accelerates the rate of range decrease because the bad cells are drained more quickly than the healthy cells, but also results in inadequate driving performance. Not being able to drive up a hill due to bad cells in a majority-healthy pack is a battery failure; exactly what the 8-year battery warranty pertains to. If they thought this should be happening on a 7.5 year old battery, then they wouldn't have made that warranty 8 years.

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Re: Rapid battery discharge, "limited motor power", and sporadic power output at temp. < 30F and > 40% motor power.

Postby VStar650CL » Sun Jan 17, 2021 12:21 pm

FurryRutabaga wrote:
Sun Jan 17, 2021 11:04 am
It's not the entire battery that cannot provide the necessary voltage at 50% throttle; it's just one or more bad cells, and because the battery management system (rightly) uses the lowest cell voltage as the indicator of available voltage from the whole pack, it sees that the voltage is too low and turns on turtle mode to accommodate.

The 5-year warranty pertains to uniform capacity lowering in an otherwise heathy pack, resulting in decreased range coupled with otherwise normal driving performance, i.e. you should still be able to drive up a hill. What I'm experiencing is the result of bad cells that have degraded disproportionately more than the healthy cells, which not only accelerates the rate of range decrease because the bad cells are drained more quickly than the healthy cells, but also results in inadequate driving performance.
Cell degradation is never uniform. It's still degradation and still not a defect like a broken wire. Semantic arguments about the language won't make it into something else, and won't make a warrantable item out of something that isn't.

FurryRutabaga
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Re: Rapid battery discharge, "limited motor power", and sporadic power output at temp. < 30F and > 40% motor power.

Postby FurryRutabaga » Sun Jan 17, 2021 4:21 pm

You're right that degradation isn't uniform, but there's also an upper limit on the amount of imbalance tolerable. Specifically because of the severe and potentially disastrous effects of high voltage imbalance between cells, e.g. suddenly losing power at highway speeds with other cars around. And no this isn't a broken wire, but the battery manufacturing process produces cells with a range of capacities, and the purpose of warranties like this is to catch parts and subsystems that may pass quality assurance testing at the time of manufacture but still fail earlier than intended. Hence there's a DTC for voltage imbalance that's taken as an indicator of bad cells and considered a warranted battery failure, unless I'm being lied to in a concerted fashion on other forums. I'll update here once this reaches a conclusion so you can have the satisfaction of being right :)

Regarding semantics, if a failure that suddenly kills power up a slight hill with a half-full battery isn't a "failure", then I don't know what is.

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VStar650CL
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Re: Rapid battery discharge, "limited motor power", and sporadic power output at temp. < 30F and > 40% motor power.

Postby VStar650CL » Sun Jan 17, 2021 5:12 pm

FurryRutabaga wrote:
Sun Jan 17, 2021 4:21 pm
Regarding semantics, if a failure that suddenly kills power up a slight hill with a half-full battery isn't a "failure", then I don't know what is.
Stopping in it's tracks would be dangerous too. The car is doing its best to compensate for a bad battery and a driver who wants free lunch.


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