Battery Lifetime

[Michael1]

[I'm not sure exactly which option you are recommending, but here is my vies. If, for example, typical daily use required 25% of the battery capacity, there are five options which one might choose (obviously there are others, this just to illustrate the point):

1. Fully charge it every four days, recharge when empty
2. Run it every day between 100 and 75%
3. Run it every day between 75 and 50%
4. Run it every day between 50 and 25%
5. Run it every day between 25 and 0 %

Even though the first option provides the fewest charging cycles, it is not the easiest on the battery, and should be avoided.

This is all well and good in BEV Geekland, but the average consumer is never going to put up with this guesswork and preplanning.

 

[leodoggie]

In the Bolt manual under battery warranty it states that 10%-40% capacity loss should be expected in the eight year 100,000 mile warranty period. Is this truely expected, or GM lawyers covering their butts. I would like to hear present EV owners Ideas about this.

 

[SeanNelson]

In the Bolt manual under battery warranty it states that 10%-40% capacity loss should be expected in the eight year 100,000 mile warranty period. Is this truely expected, or GM lawyers covering their butts. I would like to hear present EV owners Ideas about this.

A lot of it is butt covering, especially on the 40% end - although if you talk to Leaf owners they'll probably relate some discouraging stories along those lines. On the other hand, if you talk to Volt owners they'll probably tell you not to worry.

The Bolt is new, and we're not going to really know about its battery longevity for several years yet. And actual results are going to be very dependent on usage patterns and environmental factors. But GM has shown with the Volt that they're pretty conservative when it comes to rating batteries, so I have pretty positive expectations for the Bolt.

 

[Zoomit]

In the Bolt manual under battery warranty it states that 10%-40% capacity loss should be expected in the eight year 100,000 mile warranty period. Is this truely expected, or GM lawyers covering their butts. I would like to hear present EV owners Ideas about this.

A lot of it is butt covering, especially on the 40% end - although if you talk to Leaf owners they'll probably relate some discouraging stories along those lines. On the other hand, if you talk to Volt owners they'll probably tell you not to worry.

The Bolt is new, and we're not going to really know about its battery longevity for several years yet. And actual results are going to be very dependent on usage patterns and environmental factors. But GM has shown with the Volt that they're pretty conservative when it comes to rating batteries, so I have pretty positive expectations for the Bolt.

Personally, I would not look to Volt experiences and project that to the Bolt EV. The battery use cases are quite different leading to notably different limits on each battery. Those limits and use cases have direct effects on battery degradation so correlating the results could be misleading.

The other challenge is that GM could hide the battery degradation within the unusable battery capacity range and any degradation would be invisible to the owner until the usable range is effected.

I think MY15-16 Spark EVs are too new to create a statistically significant dataset on battery degradation.

 

[SeanNelson]

...But GM has shown with the Volt that they're pretty conservative when it comes to rating batteries, so I have pretty positive expectations for the Bolt.

Personally, I would not look to Volt experiences and project that to the Bolt EV. The battery use cases are quite different leading to notably different limits on each battery. Those limits and use cases have direct effects on battery degradation so correlating the results could be misleading.

My point wasn't that the Bolt batteries or use case was like the Volt, it was that GM has shown that they can do a good job with batteries. In fact they've shown a pretty consistent pattern of under-promising and over-delivering. That gives me some degree of confidence in the engineering they've done on the Bolt.

 

[Zoomit]

My point wasn't that the Bolt batteries or use case was like the Volt, it was that GM has shown that they can do a good job with batteries. In fact they've shown a pretty consistent pattern of under-promising and over-delivering. That gives me some degree of confidence in the engineering they've done on the Bolt.

I understand, but you must assume there is no degradation hidden within the Volt or Spark EV batteries, which in turn masks GM design issues, in order to make that conclusion.

 

[Fargoneandout]

I'm torn on the issue of potential battery degradation during the 100k warranty timeframe and thereafter. On the one hand Chevy has exceeded expectations everywhere else on this vehicle relative to their stated goals and, given the centrality of the battery to the vehicle and the vehicle to Chevy's long term strategy, I am willing to bet my hard earned cash that Chevy will exceed expectations in terms of battery longevitity and durability.

On the other hand the owner's manual is ominous. I downloaded the Volt owner's manual and nowhere could I see any language relating to expectations on Volt battery pack degradation. I had to go to Chevy's site and even there is just said 8 years / 100k miles, leaving aside any metrics in terms of the percentage of loss. Both packs are made by LG and LG is known to be an excellent developer and producer of such batteries. But the chemistries are not likely exactly the same. Chevy stated that the chemistry is new and the capacity per weight is higher in the Bolt-with-a-B than the Volt-with-a-V. I know both designs employ active temperature management loops and that Chevy has had a lot of practical experience with battery development technology.

Why might Chevy put specific metrics in place allowing as much as 40% battery degradation before triggering a warranty event? Lots of folks have explained likely causes: fully charging rather than Hilltop 90%, hot weather, full discharge-fully charging cycling, and more. I wonder if this isn't actually being driven by LG and not Chevy? Chevy was very aggressive in promising Bolt design, engineering, production, testing, and first to market in two years (take THAT Paul Elio) but did not have complete control over the only element really important to that success: a high-capacity battery. If the battery degrades rapidly and GM was to be on the hook for an LG design or implementation flaw, GM would want a claw-back of some kind from LG most likely (I'm totally guessing here, but.....). LG, to cover their own butts, would give GM some number that would virtually assure LG of sustaining no fails. Moreover, at the current price of what, $145 a KWh, the pack in a Bolt would be far more expensive to replace under warranty than in a Volt, who's pack is quite a bit smaller.

Dunno what to think but I do know that I'll go ahead with my purchase and keep my fingers crossed.

 

[SeanNelson]

My point wasn't that the Bolt batteries or use case was like the Volt, it was that GM has shown that they can do a good job with batteries. In fact they've shown a pretty consistent pattern of under-promising and over-delivering. That gives me some degree of confidence in the engineering they've done on the Bolt.

I understand, but you must assume there is no degradation hidden within the Volt or Spark EV batteries, which in turn masks GM design issues, in order to make that conclusion.

OR, I can assume that GM has assessed the different typical use case of the Bolt, will be much easier on the batteries than on the Volt given that they will rarely be completely "discharged" (to the point allowed by the Battery Management Software) and then fully "charged" on a daily basis the way many Volt batteries are. I am pretty much convinced that they have done this kind of assessment and have set the limits on the Bolt's batteries appropriately based on it. And, as I have said before, their track record of understanding how to manage the batteries based on expected use cases has so far been pretty good.

 

[Zoomit]

I am pretty much convinced that they have done this kind of assessment and have set the limits on the Bolt's batteries appropriately based on it. And, as I have said before, their track record of understanding how to manage the batteries based on expected use cases has so far been pretty good.

I'm very confident in their engineering team (not so much software, but that's a different question). I'm sure they engineered the usable battery capacity based on detailed use models, real examples (Volt,Spark,etc), and only marginal speculation. There's no question about that.

Clearly, there are no major battery issues with the Volts or Spark EVs that have directly affected the users, such as the early LEAFs. So any possibles issues are minor.

But we cannot say for sure how well they engineered the past batteries. Again, I think the risk of a design issue is pretty minor, but since the Volt has such a large capacity margin (and especially since it has such a large margin) it would be possible for an unexpected degradation to be masked from the owner/user. I don't have any evidence that that has occurred, but because we don't have access to the battery data, in a statistically meaningful way, we can't be positive there's no hidden issue. Lack of evidence is not evidence of absence.

One reason BEVs have such lousy resale value is the long-term uncertainty in battery costs and performance. GM could assist the secondary market values by providing us more insight into the battery condition. We don't know the Bolt EV battery total capacity nor is there an easy and definitive way to determine it's health.

 

[michael]

One of the reasons the Volt's battery lasts well is that it is limited to a relatively narrow range of SOC. This was necessary in the case of the Volt because of the way it is used. In my case, for example, it is fully charged/discharged twice every day. Despite this, it still provides the original 10.4 kWh useful capacity. Of course aggressive temperature management is also a factor as is the possibility that the SOC window is widening.

The Bolt, on the other hand has a battery that need not be fully cycled in most cases. As one poster pointed out, 200 miles 200 days a year is 40,000 miles a year...this is way above what most people use. Most days will be far less than 200 miles. So it is the responsibility of the driver to use the battery over a range of SOC that promotes long life.

For example, I drive 35 miles each way to work and have workplace charging. I could fully charge at home, and fully recharge at work. In effect, I could cycle the battery between 80 and 100% twice a day, and this would be bad for longevity. Alternatively, I can cycle it between 30 and 70% charging only at work; or between 40 and 60% charging both at home and work, either of which will be much easier on the battery. I will do something along those lines. In effect, I can be easier on the Bolt battery than the Volt is on itself.

Ideally, Chevy would have made this easier, using a slider such as Tesla provides. They didn't, but one can get around this operationally.

 

[michael]

I am pretty much convinced that they have done this kind of assessment and have set the limits on the Bolt's batteries appropriately based on it. And, as I have said before, their track record of understanding how to manage the batteries based on expected use cases has so far been pretty good.

I'm very confident in their engineering team (not so much software, but that's a different question). I'm sure they engineered the usable battery capacity based on detailed use models, real examples (Volt,Spark,etc), and only marginal speculation. There's no question about that.

Clearly, there are no major battery issues with the Volts or Spark EVs that have directly affected the users, such as the early LEAFs. So any possibles issues are minor.

But we cannot say for sure how well they engineered the past batteries. Again, I think the risk of a design issue is pretty minor, but since the Volt has such a large capacity margin (and especially since it has such a large margin) it would be possible for an unexpected degradation to be masked from the owner/user. I don't have any evidence that that has occurred, but because we don't have access to the battery data, in a statistically meaningful way, we can't be positive there's no hidden issue. Lack of evidence is not evidence of absence.

One reason BEVs have such lousy resale value is the long-term uncertainty in battery costs and performance. GM could assist the secondary market values by providing us more insight into the battery condition. We don't know the Bolt EV battery total capacity nor is there an easy and definitive way to determine it's health.

Actually, we do have some indication about absolute degradation of Volt batteries.

Idaho National Labs tests batteries in EVs over their lives. They test the actual battery capacity which cannot be masked by increasing the SOC window.

In their tests, Volt batteries showed roughly 9% loss of capacity over three years and 120,000 miles. By contrast, Spark batteries showed 3% loss over the first three months and 4000 miles.

Unfortunately, they didn't take measurements of the Volt fade over the first 4000 miles, nor do they yet have high mileage tests of the Spark. It's also true that we know all the Spark miles were on battery, but we don't know how many of the 120,000 Volt miles were on battery. But I think the handwriting is on the wall... Volt batteries last very well.

 

[leodoggie]

I have read that the LG battery used in the Bolt is a Nickel rich Lithium ion battery, which essentially means that the Anode has a lot more Nickel than Cobalt and Manganese. I tried to get my head around a couple scientific papers on this subject, with a little sucess. In a nutshell if LG has pulled this feat off, it will mean improvements in, thermal management, the battery can operate at a higher temperature. Also this can lead to more cycle times, less fade and higher energy density.

The downside is that this appears to be a new battery type so comparisons with other battery histories would be rendered mute.

If there are any battery experts ( which I am not ) out there in the forum, it would be great hear from them on this topic.

 

[Zoomit]

In their tests, Volt batteries showed roughly 9% loss of capacity over three years and 120,000 miles. By contrast, Spark batteries showed 3% loss over the first three months and 4000 miles.

INL has a small sample of Volt battery performance, but do you think their testing would have uncovered something like the LEAF battery degradation in hot climates? Obviously that issue was noticeable to LEAF owners in Arizona, but I'm not sure INL testing stressed their Volt batteries in such a way to uncover a similar issue. I think their testing is intended to characterize degradation during typical use, but not during extreme conditions.

I don't want to sound like chicken little here. I do not think there is a significant issue with GM's ability to design and build batteries. But for example, I'm sure they predicted the battery degradation of Volts that live in Arizona. Say it was 10% more than typical. We don't know how close they were with that prediction nor how they've modified their battery design for the Volt Gen2, Spark EV, or Bolt EV as a consequence.

What we do know is that any deficiencies, if they exist, haven't had an effect on owners to date. That's not trivial, and obviously something Nissan can't claim.

 

[SeanNelson]

But we cannot say for sure how well they engineered the past batteries. Again, I think the risk of a design issue is pretty minor, but since the Volt has such a large capacity margin (and especially since it has such a large margin) it would be possible for an unexpected degradation to be masked from the owner/user.

And this, I contend, is exactly one of the design decisions they made. They delivered a car with batteries that, however it's achieved, have not degraded. From my point of view that isn't "cheating" or "hiding" things, it's engineering the car to meet the expectations of users. And I expect them to have done the same with the Bolt, at least for the majority of users with "typical" usage patterns.

 

[WetEV]

In the Bolt manual under battery warranty it states that 10%-40% capacity loss should be expected in the eight year 100,000 mile warranty period. Is this truely expected, or GM lawyers covering their butts. I would like to hear present EV owners Ideas about this.

https://en.wikipedia.org/wiki/Arrhenius_equation

for many common chemical reactions at room temperature, the reaction rate doubles for every 10 degree Celsius increase in temperature.

The effective battery temperature will very likely vary by more than 10C. That's about a factor of two at minimum. Change and discharge rates will vary a lot. Charge profiles will vary a lot. Battery chemistry is new. 10% to 40% is realistic. Or at least, that's my take on the matter. Leaf owner.

 

[michael]

In their tests, Volt batteries showed roughly 9% loss of capacity over three years and 120,000 miles. By contrast, Spark batteries showed 3% loss over the first three months and 4000 miles.

INL has a small sample of Volt battery performance, but do you think their testing would have uncovered something like the LEAF battery degradation in hot climates? Obviously that issue was noticeable to LEAF owners in Arizona, but I'm not sure INL testing stressed their Volt batteries in such a way to uncover a similar issue. I think their testing is intended to characterize degradation during typical use, but not during extreme conditions.

I don't want to sound like chicken little here. I do not think there is a significant issue with GM's ability to design and build batteries. But for example, I'm sure they predicted the battery degradation of Volts that live in Arizona. Say it was 10% more than typical. We don't know how close they were with that prediction nor how they've modified their battery design for the Volt Gen2, Spark EV, or Bolt EV as a consequence.

What we do know is that any deficiencies, if they exist, haven't had an effect on owners to date. That's not trivial, and obviously something Nissan can't claim.

Of course the INL testing was sufficient to reveal the differences between Leaf and Volt battery fade. Why do EVers constantly dismiss as irrelevant research by recognized experts in the field??

The INL testing that showed Volts down typically 9% at three years and 120,000 miles showed Leafs down typically 14% at 14 months and 14,000 miles

I do agree with the idea that increasing the SOC window to mask battery fade is a legitimate engineering approach, not a deception. However it needs to be understood that this approach does not eliminate the problem of fade, only delays its effect. In fact it accelerates the fading process as the battery is subject to progressively widening SOC windows

 

[SeanNelson]

I do agree with the idea that increasing the SOC window to mask battery fade is a legitimate engineering approach, not a deception. However it needs to be understood that this approach does not eliminate the problem of fade, only delays its effect. In fact it accelerates the fading process as the battery is subject to progressively widening SOC windows

Yes, but the real goal is a car whose battery has a useful range throughout the life of the vehicle. Whatever gets you there is valid, as far as I'm concerned.

 

[michael]

Right. That's what I said, an engineering choice, not a deception

 

[Zoomit]

Of course the INL testing was sufficient to reveal the differences between Leaf and Volt battery fade. Why do EVers constantly dismiss as irrelevant research by recognized experts in the field??

The INL testing that showed Volts down typically 9% at three years and 120,000 miles showed Leafs down typically 14% at 14 months and 14,000 miles.

Your frustration seems aimed at me so let me say that I'm definitely not dismissing the controlled testing that INL does. I would certainly expect them to identify differences in degradation, especially under typical conditions. I'm simply not familiar with their methodology and don't know if they tested extremes.

The question I had is not whether their testing noted a discrepancy between the Volt and LEAF. The question was whether their test methodology is expected to uncover and statistically isolate effects that are only seen in extreme conditions or corner cases.

 

[michael]

My frustration includes your response (not you!) and extends to many people in the EV world who have an unsupported opinion (or one supported by some vague internet source such as "Battery University" and refuse to accept peer-reviewed, published research by identified experts at INL, NREL, universities, etc.

It's like I have an article in the New England Journal of Medicine that presents research results, and someone says, I don't care, it's wrong, here's what it says at WebMD...