Volt vs. Leaf - What finally pushed you to the Leaf?

[KJD]

Volt: 38 miles all-electric
Plug-in Prius: 11 miles all-electric

LEAF = 75 miles all electric

This is what pushed me to the LEAF and I have no regrets at all.

 

[cracovian]

I didn't like the Volt at all. Seemed cramped. Had dumb non navigation touchscreen. Can't haul kids and kid crap very well. Car seats had no chance of fitting. It ended up in 4th place of 4 cars considered behind the leaf, prius, and dodge charger with a hemi. It was the most expensive also lease wise. So most expensive, least useful, and least comfortable. I guess if I was kid less and tiny it would be ok.

That's an unusual choice of candidate, given the other three. It's almost like one of those logic questions that asks you which of the following does not belong in this list:

A) Leaf
B) Prius
C) Volt
D) Dodge Charger with a Hemi

If we were to apply logic to car ownership we would all be driving Corollas. I had to get a van instead of my GTO coming off lease and I would honestly still drive that 5.7 liter beauty if I were alone. I'd still pick that sucker over LEAF and stuff Bedouin pockets with my gas money if I could You can make a case for any car really... Just because you're green and stuck with an eco mobile, it doesn't mean you don't get "crazy" thoughts sometimes and even act up on 'em... It's all good.

 

[RegGuheert]

Here are the top issues with the Volt that caused us to choose the LEAF:

1) $10,000 - The difference in price between a new 2012 Volt and a demo 2011 LEAF with the same features when we purchased.
2) Back seat - As mentioned, LEAF has three while Volt has only two. More significantly, the Volt directly above the rear passengers' heads. Our boys told me they were uncomfortably hot during the test drive. They like the back seats in the LEAF because they sit up high and can see well.
3) Battery life - Now, to start this topic, please note that given the fact that the Volt includes a TMS and the LEAF does not, there are LOTS of places and applications where the LEAF will have much worse battery life than the Volt. But I'm convinced in our location and in our application, the battery in our LEAF will last longer than the one in a Volt, had we purchased that.

Here is my reasoning: Most of our trips are 25-35 miles with a weekly 50-mile excursion and an very occasional 75-mile trip. Assuming similar energy economy on these trips, the most frequent trip will result in a lower DOD in the LEAF than in the Volt given the capacity of the LEAF battery is 50% higher than the capacity of the Volt battery. This would also be true for the weekly 50-mile trip. For the 75-mile trip, the DOD in the LEAF is probably higher. It remains to be seen whether the effects of the local climate will hurt the LEAF battery life more than the lower DOD will help it. For the vast majority of the year, the LEAF battery would likely be colder than the Volt battery, but there are a couple of weeks of the year where would be higher. I still think the lower DOD will put the LEAF ahead in battery life here. In Seattle, where the OP lives, I'm pretty sure a LEAF battery will last longer than a Volt battery unless you regularly drive 70 miles or more.

But battery life may only be a consideration if you plan to keep the car for a long time like we do.

 

[SanDust]

Your statement assumes more trips, in absolute numbers not mileage, beyond LEAF range—requiring the backup ICE car—than trips beyond Volt electric range but within LEAF range. While likely true for some households, but not others, your blanket statement is a stretch. "Statistics" depend a whole lot on the underlying assumptions.

I certainly did not limit the analysis to those days with 40 miles or less of driving. I did assume more daily driving beyond 75 miles than between 40 and 75 miles -- which is the reason why the Volt produces more EV miles than the Leaf -- but that's because this is the reality of the situation. According to the Office of Highway Policy Information, the breakdown of daily vehicle miles is as follows:

00-01: .4% of days
01-10: 24.2% of days
10-20: 21.2% of days
30-50: 13.9% of days
50-75: 6.6% of days
75-100: 2.9% of days
100+: 17.1% of days

The short story is that since the Leaf can't go more than 75 miles a day, the average driver will park the Leaf and take another car, rent a car, or something 20% of days. For these days the Leaf will rack up 0 EV miles while the Volt will rack up 40 EV miles. The Leaf can eat into this by racking up, at most, 10 more miles than the Volt on 6% of the days (40-50 miles) and say 25 miles on another 6.6% of the days (50-75 miles). But since .2(40) is a much larger number than .06(10) + .066(25), almost 4x larger, the arithmetic shows the average driver will get more EV miles from a Volt than a Leaf.

Counter intuitive I know. I was surprised when I ran the numbers the first time. A few notes:

1. The point that there isn't nearly as much range difference between the cars than some would think isn't directly relevant. It just makes the Volt get more EV miles.

2. You can of course claim that you can charge the Leaf multiple times and day and so forth but you have to then assume the same holds true for the Volt. The conclusion won't change.

3. You correctly point out that this is the average driver and that some drivers might get a different result. That's perfectly true but on average it can't be true.

 

[Volusiano]

For the vast majority of the year, the LEAF battery would likely be colder than the Volt battery

Are you saying that this is better or worse for the LEAF battery, being colder because the LEAF doesn't have TMS so its battery is closer to the colder winter ambient temperature than the nice and warm Volt battery thanks to its TMS if plugged in prior to use?

And how is winter time the vast majority of the year? Even for cold states like MN, winter is only about 1/2 of the year.

 

[RegGuheert]

For the vast majority of the year, the LEAF battery would likely be colder than the Volt battery

Are you saying that this is better or worse for the LEAF battery, being colder because the LEAF doesn't have TMS so its battery is closer to the colder winter ambient temperature than the nice and warm Volt battery thanks to its TMS if plugged in prior to use?

Yes. Being cold is not great for range, but it should help battery life.

And how is winter time the vast majority of the year? Even for cold states like MN, winter is only about 1/2 of the year.

I did not say that winter was most of the year. I said that I expect the LEAF battery to be colder than a Volt battery in our service for much more of the year. Average temperatures around here are very rarely above 72F.

 

[SanDust]

3) Battery life - Now, to start this topic, please note that given the fact that the Volt includes a TMS and the LEAF does not, there are LOTS of places and applications where the LEAF will have much worse battery life than the Volt. But I'm convinced in our location and in our application, the battery in our LEAF will last longer than the one in a Volt, had we purchased that.

Here is my reasoning: Most of our trips are 25-35 miles with a weekly 50-mile excursion and an very occasional 75-mile trip. Assuming similar energy economy on these trips, the most frequent trip will result in a lower DOD in the LEAF than in the Volt given the capacity of the LEAF battery is 50% higher than the capacity of the Volt battery.

The other reasons for your choice make sense but you're most certainly wrong on this. The Leaf battery isn't 50% larger. It's 25% larger. While this does mean that if you drive the same number of EV miles on both cars -- and the math says you'll actually put more on the Volt -- you will put more cycles on the Volt battery than on the Leaf battery.

However, the DOD will always be less on the Volt since the Volt only uses about 65% of the cell capacity whereas the Leaf uses 80%. Less DOD means longer life. FYI this was discussed in an article by Tony Markel a few years back: http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/43159.pdf" onclick="window.open(this.href);return false; His research concluded that many discharges in the middle of a cell SOC had negligible effect on battery degradation compared to even a single DOD of 80% (page 13). The paper suggests the Nissan approach of using more of the battery is better because it will achieve a higher market penetration since the cost per usable kWh will be lower, but it also shows that using a higher DOC will result in a much less range at the EOL and an EOL that occurs sooner rather than later.

I also suspect the LG Chem cells will last longer because they have inert layers of magnesium but we'll have to wait on that. What we do know is that GM warrants capacity for ten years whereas Nissan doesn't warrant capacity at all.

Short story is that the Volt is a better long term bet as far as the battery is concerned. Concerns about the Leaf battery was one of the reasons I chose to lease. It's also not as if you were penalized if you leased. The only difference was the acquisition fee, which wasn't that much.

 

[RegGuheert]

The Leaf battery isn't 50% larger. It's 25% larger.

24kWh/16kWh= 1.5

However, the DOD will always be less on the Volt since the Volt only uses about 65% of the cell capacity whereas the Leaf uses 80%.

If I drive 30 miles RT, how is my DOD 80%?

Edits: Problems with quotes.

 

[DaveEV]

The other reasons for your choice make sense but you're most certainly wrong on this. The Leaf battery isn't 50% larger. It's 25% larger.

You know, if you're going to go out of your way and correct someone, you should at least be sure that you're right. :roll:

The LEAF battery at 24kWh IS 50% larger than the Volt's 16 kWh battery. OK - I may give you 5% if you use the '12 Volt's 16.5 kWh battery - the LEAF's battery is "only" 45% larger than that one.

16 * 1.5 = 24
16.5 * 1.45 = 24

 

[Reddy]

The Leaf battery isn't 50% larger. It's 25% larger. While this does mean that if you drive the same number of EV miles on both cars -- and the math says you'll actually put more on the Volt -- you will put more cycles on the Volt battery than on the Leaf battery.

I thought the Volt's battery was 16 kWh and the Leaf's was 24 kWh.
http://en.wikipedia.org/wiki/Chevrolet_Volt
http://en.wikipedia.org/wiki/Nissan_Leaf

Yes, how much we chose to use or how much the manufacturer lets us, is certainly different. But if driving short distances in either car, say 20 mi at 4 mi/kWh and using 5 kWh, it seems to me that the DOD for the Leaf is much less than the Volt. Just because the manufacturer keeps a higher percentage of the Volt's battery inaccessible to the user doesn't change the total %DOD. Am I missing something?

Edit: Sorry to pile on. It looks like others have said the same thing while I was typing.

 

[SanDust]

The Leaf battery isn't 50% larger. It's 25% larger.

24kWh/16kWh= 1.5

However, the DOD will always be less on the Volt since the Volt only uses about 65% of the cell capacity whereas the Leaf uses 80%.

If I drive 30 miles RT, how is my DOD 80%?

Edits: Problems with quotes.

Yeah, it's 50%. My mistake. I was thinking 16/20 for some reason. Doesn't change anything.

When going 30 miles your DOD isn't 80%. But you say you go 75 miles and that is going to be a fairly deep DOD. Also if you're going 30 miles the DOD for the Volt isn't an issue either. Just can't see any scenario where the Leaf battery outlasts the Volt's, given that the Volt is using less of the cells and has a TMS. It may not get to 90F in Seattle that often but it does happen.

 

[RegGuheert]

But you say you go 75 miles and that is going to be a fairly deep DOD.

We do that trip about six times a year. Last time I made that trip was in January. I arrived home with two bars, which is at or above the point where the VOLT would stop its discharge. This is typical for this trip. Note that in the LEAF it is possible to charge for 90 minutes prior to a trip to bring the SOC up from 80% to 94%. This allows us to minimize the DOD on longer trips.

Also if you're going 30 miles the DOD for the Volt isn't an issue either.

We make this type of trip about four times a week, maybe more. Others here have posted that in the wintertime they get less than 25 miles in the Volt. That means that in cold weather the Volt would be brought down to about 21% SOC with each wintertime trip. By comparison, the LEAF would be charged to full just before the trip and would arrive home with six or seven bars, or an SOC around 60%.

Then that leaves our 50-mile weekly excursion. Again we typically charge to full just before the trip and return home with about four bars, or about 40% SOC. The Volt would be brought to about 20% during this trip.

Just can't see any scenario where the Leaf battery outlasts the Volt's, given that the Volt is using less of the cells and has a TMS.

Many people, including you, have touted the statistic that Volts drive more EV miles than LEAFs. If that is true, then it seems the Volts are typically brought to a much lower SOC than the LEAFs, particularly since the SOC in the LEAF can be brought up to a higher level before departure.

It may not get to 90F in Seattle that often but it does happen.

A LEAF battery at 90F should degrade twice as fast as a Volt battery at 72F. And, unfortunately, the LEAF will quickly come up to ambient temperature when driven, but will slowly approach ambient when parked. This has the effect that the LEAF battery tends toward the day's high temperature instead of the average temperature, assuming it is driven. Around here in July and August, the average highs are in the mid 80Fs and the average temperatures are 73F to 74F. During those months, our LEAF battery may degrade 50% faster than a Volt's battery. During the spring and fall, it's probably a wash and for about five months in the winter, the Volt's battery likely degrades at 2X to 4X the rate of the LEAFs, at least when it is heated to temperature. But the Volt is going to a lower SOC each time it is driven and it sits at a higher SOC (86.5% versus 80% or lower) when it is not driven.

So, does the couple of months of slightly higher calendar degradation in the LEAF in the middle of the summer fully offset the higher calendar degradation in the Volt during the wintertime plus the year-round higher SOC when sitting charge plus the year-round lower SOCs achieved with virtually every trip? Maybe, but I doubt it.

As I said initially, clearly the LEAF will do much worse than the Volt in hot climates, and this is borne out by user experiences. But, for us I don't see the point in purchasing a car with an smaller battery and an expensive TMS system which will use more electricity and likely have a shorter battery life.

The only way I can see the Volt having a better battery life in our scenario is if there is something much better in the chemistry itself. That may be the case, but I had no way to judge that at the time of purchase.

 

[Volusiano]

For the vast majority of the year, the LEAF battery would likely be colder than the Volt battery

Are you saying that this is better or worse for the LEAF battery, being colder because the LEAF doesn't have TMS so its battery is closer to the colder winter ambient temperature than the nice and warm Volt battery thanks to its TMS if plugged in prior to use?

Yes. Being cold is not great for range, but it should help battery life.

Where did you get your source that being cold is better for battery life? I'd like to see it.

The conventional wisdom is that being hot is bad for battery life. But this doesn't imply that the opposite, being cold is better for battery life.

Another conventional wisdom is that being cold hurts range but doesn't hurt battery life. But this doesn't imply that cold is better for battery life either.

This chart says that the ideal temperature band for the Volt battery is 68F-72F. Note that it doesn't say that 25F-68F is the ideal band. It doesn't define what ideal band is. It could be for range, or life, or both. But I have never read from any source that says that cold is better for battery life. So I'd like to see your source on this.

 

[Den]

Where did you get your source that being cold is better for battery life? I'd like to see it.

It's said in this sites wiki. And there is a table where Battery will live most. Coldest places (like Alaska or Norway) are the winners with about 20 years. When for Arizona same age is about 3 years.

 

[RegGuheert]

Where did you get your source that being cold is better for battery life? I'd like to see it.

I'm simply applying the Arrhenius equation which describes the temperature dependence of reaction rates. Simply put, reaction rates double for each 10C increase in temperature and drop by half for each 10C drop in temperature.

The conventional wisdom is that being hot is bad for battery life. But this doesn't imply that the opposite, being cold is better for battery life.

Another conventional wisdom is that being cold hurts range but doesn't hurt battery life. But this doesn't imply that cold is better for battery life either.

In a way, conventional wisdom is correct, since doubling of the degradation reactions is a bigger change than halving it. Still, the conventional belief that there is some magical switch that turns on degradation above 70F is wrong.

This chart says that the ideal temperature band for the Volt battery is 68F-72F. Note that it doesn't say that 25F-68F is the ideal band. It doesn't define what ideal band is. It could be for range, or life, or both.

If you are controlling temperature of a battery, you choose a temperature band which gives you the highest temperature which will meet your goals for battery life.

But I have never read from any source that says that cold is better for battery life. So I'd like to see your source on this.

The Arrhenius equation is a well-known effect and it is used extensively to help predict the life of many things, including batteries, oxidation of paint, wear out of electrolytic capacitors, etc. It's the reason all of our cars are white!

 

[Volusiano]

But I have never read from any source that says that cold is better for battery life. So I'd like to see your source on this.

The Arrhenius equation is a well-known effect and it is used extensively to help predict the life of many things, including batteries, oxidation of paint, wear out of electrolytic capacitors, etc. It's the reason all of our cars are white!

Sure, you don't need an empirical equation to know that common sense says things in the cold last longer, and that's why we have refrigerators and freezers for our foods, no doubt about it. But I thought you went to the trouble to make that point because you got a source somewhere (maybe a publication from a battery manufacturer) that quantitatively shows how SIGNIFICANT lithium ion batteries' life can be increased by keeping them stored in the cold.

It really depends on how fast things degrade and at what temperature the degradation would accelerate. For example, not ALL foods need to be kept in the fridge so they don't spoil. Certain kinds of food can be kept at room temperature and can still last a long time before they go bad. Long enough that you'd probably eat them already before they ever go bad.

I haven't read anywhere that leaving a lithium ion battery at room temperature will cause it to degrade significantly enough over its useful lifetime of 10-20 years, such that manufacturers deem it important enough to keep it at a more chilled temperature than say 70F. So if the ROI of keeping it at colder temperature for slower degradation during its useful lifetime is not signification enough, why bother belabor the point? If manufacturers don't bother, why should we?

It's kinda like saying we shouldn't put a rock under the waterfall if we don't want to rock to be diminished in size by the water flow. But how long will the waterflow take to wear the rock down enough that we will notice the difference in its size? Not during our lifetime!

 

[DaveEV]

Seriously Volusiano? Lithium Battery Temperature Life Storage

Link #2: http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries" onclick="window.open(this.href);return false;
See Table 3: Estimated recoverable capacity when storing Li-ion for one year at various temperatures

There are lots more, including scientific papers if you wish to read more.

 

[Volusiano]

Seriously Volusiano? Lithium Battery Temperature Life Storage

Link #2: http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries" onclick="window.open(this.href);return false;
See Table 3: Estimated recoverable capacity when storing Li-ion for one year at various temperatures

There are lots more, including scientific papers if you wish to read more.

Yes, this is exactly what I was asking for. Thank you!

I'm definitely more convinced by the table 3 of the Battery University paper than the Arrhenius equation explanation.

 

[surfingslovak]

Interesting discussion, I don't have much time for the remainder of the week, but you might want to look at this technical paper from NEC, which was posted on the forum earlier. There were many questions about the validity of the Arrhenius equation, and its applicability to the battery pack in the LEAF. Similarly, a question was raised about the activation energy and the applicability of the 10-degree-Celsius rule.

NEC is Nissan's partner in the AESC joint venture, which manufactures the battery packs for the LEAF, and I would consider them to be a relevant source. Perhaps even more so than the Battery University.


Click to open

I don't know why the TMS table from the Volt forum indicated that the pack should not get colder than 25 F. I don't think that there is anything that would preclude the battery from being stored at a lower temperature, and this should be beneficial to calendar life.

On the other hand, the situation could be a bit different when operating the vehicle. Li-ion batteries generally don't like being charged when they are cold. I recall reading about an effect called lithium plating, which is detrimental to the longevity of these batteries. This might be the reason why regen and charge rates are limited in cold weather. It might also help explain why the Volt is heating its battery pack when ambient temps drop below the freezing point.

What Volusiano said about GM's capacity warranty is very valid, and several posters mentioned that when Nissan made the original announcement last Decemeber. The consensus was that technically Nissan was correct, because the LEAF is a full EV, and the Volt, for all its merits, is a plugin hybrid. Personally, I don't think that they needed to sneak this statement in there, because it's a bit misleading, and can be seen as disingenuous. Given everything that transpired last year, it might not have been the right occasion to sound celebratory.

Nevertheless, Nissan voluntarily extended a retroactive warranty. Although it was in everyone's best interest, they didn't have to do that. GM, on the other hand, might not have had a choice, because the Volt carries gasoline on board, and the battery pack is technically covered under emissions regulation. Should the battery lose a lot of capacity, more emissions will be created by burning gas. While this might be regulated, the loss of capacity for a pure EV is not, and it's up to the manufacturer to offer a capacity warranty. Perhaps this is what Nissan was trying to convey.

 

[Volusiano]

I don't know why the TMS table from the Volt forum indicated that the pack should not get colder than 25 F. I don't think that there is anything that would preclude the battery from being stored at a lower temperature, and this should be beneficial to calendar life.

From the range perspective (not capacity perspective), I think it would make sense that the ideal temperature band is 68F-72F, because storing the battery at colder temperature may be better capacity, but it's not better for range.

So in trying to balance the 2, the effect on capacity at colder temperature is not as significant as the effect on range, so it makes sense that its ideal temperature band should 68F-72F to optimize on the range with minimal effect on capacity. Remember, after all, this TMS chart is for optimum OPERATION of the Volt battery, not optimum STORAGE of the Volt battery.

Also as you can see from this chart, 25F-68F does not have any "action" associated with it, even when in parked/plugged in model. If you read the whole thread carefully, it's simply because the person who came up with the chart could not find any clear indication of how the Volt behaves during this temperature range, so they simply left it alone. But if I have to guess, if the Volt is parked and plugged in, and the temperature is at slightly above 25F (which is well below freezing), I'm pretty sure that the TMS will try to "preheat" the battery to something much warmer than 25F. I would venture to guess that it would most likely be in the "warming" cycle as well.

So the claim that being in a colder climate for the majority of the year is an advantage for the battery like RegGuheert originally claimed is a double edge sword. I would rather be in milder climate (68F-72F) than be in colder climate (25F-68F) so I can get much more improved range at a tiny expense of capacity loss.

That's why I decided to call it out, because to me the range advantage of milder climate far outweighs the minimal capacity advantage of much colder climate.