Gen 1 GM Volt Plug-In Hybrid (2011-2015)

[RegGuheert]

I recall that the rate of Battery capacity loss and whether the Volt BMS would maintain Range by accessing a greater percentage of total capacity has been of interest to many.

There is a great deal of DOE test data on the Volt Available here:

http://avt.inel.gov/phev.shtml" onclick="window.open(this.href);return false;

You may want to look at the recent report below:

Thanks, Ed! Good find!

2011 Chevrolet Volt VIN 0815 Plug-In Hybrid Electric Vehicle Battery Test Results
Tyler Gray
Jeffrey Wishart
Matthew Shirk
July 2013
The Idaho National Laboratory is a U.S. Department of Energy National Laboratory
Operated by Battelle Energy Alliance....

1.6 Conclusion
The testing of Chevrolet Volt 0815 included BOT and EOT battery tests and 14,836 miles of fleet testing in between. For vehicle battery packs, end-of-life (EOL) criteria is determined to be when the discharge capacity or discharge energy degradation exceeds 23% of the rated value, as specified in the USABC Electric Vehicle Battery Test Procedures Manual Rev 3 (publication pending). The Chevrolet Volt with VIN 0815 experienced a degradation of 2.2% in battery capacity. The battery of Chevrolet Volt 0815 is therefore well below the EOL threshold. The battery of Volt 0815 also had a degradation of 12.9% and 6.3% in discharge and charge power capability at 80% and 20% DOD, respectively, over the duration of 14,836 miles of fleet testing

http://avt.inel.gov/pdf/EREV/battery2011volt0815.pdf" onclick="window.open(this.href);return false;

It is a very strange conclusion, given what I read in the report. They act as if the battery is only 2.2% below its rated capacity at the end of the test. By my reading, the battery is either 7%, 9% or 11% down at the end of the test. Take your pick! Should I believe Table 1, which contains a starting capacity well below the Volt batteries rated capacity and an ending capacity which is only slightly lower? Or should I believe Table 3, which contains a staring capacity closer to the rated capacity and a lower ending capacity, with the two numbers showing a more linear loss of capacity?

In Table 3 we see that the battery started the test after the car had driven 8478 miles with 97% of its rated capacity of 16 kWh and ended the test after a total of 23,314 miles with only 89% of the rated capacity left. In other words, it lost 8% of the rated capacity in the 14,836 miles of this test and 11% of rated capacity since new (possibly more or less, since the battery was never tested new). The constant-power discharge used to determine the figures in Table 3 are very appropriate for EV application, IMO.

Sorry, but the numbers in Table 1 that are quoted in the conclusion make virtually no sense.

Not sure myself whether the relatively short time and low miles between the two tests allows definitive conclusions about the longer-term rate of Volt battery capacity degradation, but have any with much higher miles on their Volts seen any loss of range from new yet, as would seem likely by now if the percentage of available battery capacity percentage was being held constant by the Volt's BMS?

It seems clear the BMS is doling out capacity as the battery degrades, just as was originally reported. I will repeat that I think this is a very clever scheme.

Maybe some of the volt drivers or battery/power experts here here can explain the implications of the much larger percentages in the "degradation of...discharge and charge power capability" reported, and why the authors seem to find it significant enough to put it in the conclusion.

Like I said, the conclusion is weird. The important numbers to an owner are found in Table 3, IMO.

Is that (entirely, largely, or partially?) due to the increased battery resistance (charts on p. 4) in Charge and discharge mode?

Entirely, methinks.

What does that suggest about Volt battery/vehicle performance?

I think the Volt battery is doing roughly what everyone should expect: It is degrading with use. The numbers are decent for a battery that is 2/3 the capacity of what is included in the LEAF.

Is there a thread or threads on a volt forum where these DOE reports are being discussed?

Good question.

 

[edatoakrun]

Is there a thread or threads on a volt forum where these DOE reports are being discussed?

...Good question.

See:
http://gm-volt.com/forum/showthread.php?60874-Battery-degradation-range-loss-(if-you-have-any-post-amount-age-miles-and-testing/page9" onclick="window.open(this.href);return false;

="RegGuheert"
...It is a very strange conclusion, given what I read in the report. They act as if the battery is only 2.2% below its rated capacity at the end of the test. By my reading, the battery is either 7%, 9% or 11% down at the end of the test. Take your pick! Should I believe Table 1, which contains a starting capacity well below the Volt batteries rated capacity and an ending capacity which is only slightly lower? Or should I believe Table 3, which contains a staring capacity closer to the rated capacity and a lower ending capacity, with the two numbers showing a more linear loss of capacity?...

I will try to take a closer look at your post, and the report, in the AM.

I thought that it seemed to be reporting that while the test Volt's battery capacity has degraded only ~2.2%, the large increase in charge and discharge resistance means that there is a very large reduction in both charge and discharge efficiency, and the decreased discharge efficiency was the primary cause for the DC kWh out of the pack decreasing from ~15.6 kWh to ~14.3 kWh (from table 3-when discharged at 15.25 kW) over the ~15,000 miles between the tests.

But this was so unexpected, I thought I likely was misreading the report.

BTW, I have considered that a large decrease in charge/discharge efficiency could explain much of the anomaly between my LEAF's ~16% loss of available battery capacity, as reported by the app, and by my LEAFs dash/nav screen/Carwings kWh reports, and the fact that my 16A/240V recharge times from ~VLBW to "80% are nearly the same as they were ~2 years ago.

But that would still mean I've somehow figured out to get ~the same range I was getting ~2 years ago, on the ~16% fewer (DC from the battery?) kWh that all these sources report.

And I also think the large increase in my LEAFs battery heating while charging/discharging would also have been noticeable.

Of course, with the Volt battery pack's ATM ...

 

[blackmamba]

GM has always made a big deal to describe the Volt as a BEV with range extender. Only very reluctantly admitting that the engine can mechanically power the wheels. This makes it not much different from any other hybrid out there. The electric motor can drive the vehicle or the gas engine. Not sure why it's so hard to admit and needs to be so nuanced.

I fail to see why this keeps on coming up as an "issue". It's completely irrelevant!

1. The range extender never comes on unless battery SOC gets too low or if the battery gets too cold.
2. Having the range extender directly power the wheels when it's already running improves efficiency!

So who really cares that when the range extender comes on it will direct some power directly to the wheels when it's beneficial to do so. Would you rather the range extender only generate electricity and suffer from lower efficiency?

I think the issue is with the use of semantics. Used cars are now "pre-owned". And a series/parallel gasoline-electric hybrid is now an "Electric car with a gasoline-powered range-extender". Its a story of an apple by any other name (or a duck). PR/PC speak is just another way of lying to yourself and others, when you paper over (or "Astroturf") specifics. That's the issue that some people don't like, and I have to say I'm one of them.

I agree GM should let the car speak for itself, but not at the expense of the truth.

Then by your judgment, the BMW i3 with Rex cannot be correctly termed an EV, or even correctly termed an Electric car with a gasoline-powered range extender. WHat is it, then? Are you going to call BMW a liar if they refer to the i3 Rex as an EV with extended range?

 

[scottf200]

It seems clear the BMS is doling out capacity as the battery degrades, just as was originally reported. I will repeat that I think this is a very clever scheme. I think the Volt battery is doing roughly what everyone should expect: It is degrading with use. The numbers are decent for a battery that is 2/3 the capacity of what is included in the LEAF.

As you pointed out the report has quite a mix of numbers.

I just got home a short while ago and went 50 miles on the battery today on my 2011 Volt. I only ran the ECO A/C for 2/3rds of the drive as the weather was great.
It has 24,299 EV only miles out of 31,242 total miles.

 

[RegGuheert]

It seems clear the BMS is doling out capacity as the battery degrades, just as was originally reported. I will repeat that I think this is a very clever scheme. I think the Volt battery is doing roughly what everyone should expect: It is degrading with use. The numbers are decent for a battery that is 2/3 the capacity of what is included in the LEAF.

As you pointed out the report has quite a mix of numbers.

I just got home a short while ago and went 50 miles on the battery today on my 2011 Volt. I only ran the ECO A/C for 2/3rds of the drive as the weather was great.
It has 24,299 EV only miles out of 31,242 total miles.

The BMS design in the Volt has resulted in an excellent user experience. Unfortunately, it has not allowed for any estimation of the life of the battery.

But I can make an estimate from Table 3 used in the report. When new, the 2011 Volt used 10.5 kWh from a battery with a 16 kWh nameplate capacity, or about 66% of the capacity. Rounding the miles to 25,000, we see that the test vehicle now uses 10.5 kWh out of 13.9 kWh or about 75% of the total capacity. If we assume linear degradation (which may be optimistic, assuming the increasing DOD that will occur with any degrading battery) and pick 95% of total capacity as the maximum value the BMS will use, we can see that users will not see the degradation until the battery degrades to a capacity of 11 kWh or a degradation of 32%. This should not occur until about 75,000 miles in the test scenario used. Assuming battery warranty kicks in at 70% of 10.5 kWh available or 7.35 kWh available, the warranty would not kick in until the battery has degraded to 7.73 kWh of capacity or 48% of original capacity. At a degradation rate of 11% per 25,000 miles, this should not happen for about 120,000 miles.

I predict that GM will have very few warranty claims for the batteries in the Volt due to capacity loss. Once the user starts to experience range degradation, they should be able to drive about 50% further before they can warranty the battery.

TMS will help the experience to be more uniform in different climates, but we should expect more degradation in hotter climates like Phoenix. Given that, I would expect some owners to start seeing reduced range within the next year. Perhaps that is what we are seeing in the poll that Scott posted. It would be interesting to know how many of those who see the small depredation are in a hot climate.

Thoughts?

 

[edatoakrun]

RegGuheert,

Remember the capacity test you are discussing was at ~15.25 kW, which occurs at what, about 55mph level speed?

The available (DC from the battery) capacity could be higher at higher discharge efficiency, at lower kW.

What I think all these DOE tests may be showing, is declining discharge efficiency for the Volt at higher kW rates, which is further exacerbated over time and miles driven. The large decrease in discharge (and recharge) efficiency over only ~ 7 months and ~15,000 miles, is what I find puzzling.

Any experts on Volt battery chemistry that can explain this?

As I posted previously, there are further Volt test results at:

http://avt.inel.gov/phev.shtml" onclick="window.open(this.href);return false;

Look at:

2011 Chevrolet Volt – VIN 0815
Advanced Vehicle Testing – Baseline Testing Results

http://avt.inel.gov/pdf/EREV/fact2011chevroletvolt.pdf" onclick="window.open(this.href);return false;

I believe this is the BOT in the later test you have been referring to.

Notice that when "new" (~8,000 miles) this Volt's discharge efficiency is considerably lower at higher kW, resulting in discharge efficiency of only ~92% (as gauged by recharge capacity) resulting in range of only ~ 27.4 miles, in the 70 mph constant speed test.

Does that range at ~70 mph (at all the other controlled test variables) sound about right to the Volt drivers?

CONSTANT-SPEED RANGE AND CHARGE TESTING IN CHARGE-DEPLETING MODE1
45-mph Test2,3
60-mph Test2,4
70-mph Test2,5
Average DC power out of battery (kW):
10.1
17.5
22.8
(A) DC energy out of battery (kWh):
9.4
9.0
8.9
Battery capacity discharge (Ah):
26.0
25.1
24.9
(B) Total distance traveled (mi)6:
42.9
31.0
27.4
(C) Post-test charge AC energy from EVSE @ 240 V to onboard charger (kWh):
11.1
11.3
11.2
(D) Post-test charge DC energy into battery from onboard charger (kWh):
9.7
9.6
9.7
Post-test charge duration (HH:MM):
03:35
03:45
03:45
AC electricity consumption rate (Wh/mi)7:
259
341
409
DC electricity consumption rate (Wh/mi)8:
226
290
325
(A/D) Battery Roundtrip Efficiency9:
97%
94%
92%
(D/C) On-Board Charger Efficiency10:
87%
85%
87%
(A/C) Overall Trip Efficiency11:
85%
80%
79%

 

[scottf200]

Notice that when "new" (~8,000 miles) this Volt's discharge efficiency is considerably lower at higher kW, resulting in discharge efficiency of only ~92% (as gauged by recharge capacity) resulting in range of only ~ 27.4 miles, in the 70 mph constant speed test.

Does that range at ~70 mph (at all the other controlled test variables) sound about right to the Volt drivers?

This is from last Saturday 10Aug2013 and I was driving 70 mph following a friend up to a MI lake. 39.6 EV miles with ECO A/C on.

 

[DaveEV]

The available (DC from the battery) capacity could be higher at higher discharge efficiency, at lower kW.

It definitely is. At 10.1 kW / 45 mph they get 9.4 kWh out of the battery, at 17.5 kW / 60 mph they get 9.0 kWh out of the battery and at 22.5 kW / 70 mph they get 8.9 kWh out of the battery.

Their energy from the wall to charge the battery seems low, though, at 11.1-11.3 kWh. Don't most Volt owners report around 13 kWh from the wall to recharge? The range they are getting seems very low as well from what most people report. At least they appear to be consistent - their LEAF testing also shows lower range than what most would expect.

 

[scottf200]

Their energy from the wall to charge the battery seems low, though, at 11.1-11.3 kWh. Don't most Volt owners report around 13 kWh from the wall to recharge?

Varies based on 120v or 240v charging.

Example: http://www.edmunds.com/chevrolet/volt/2011/long-term-road-test/2011-chevrolet-volt-changing-battery-performance-over-time.html" onclick="window.open(this.href);return false;

On average, it took 12.2 kilowatt-hours (kWh) to fully charge the battery using the 240-volt charger in our Santa Monica parking garage. That figure rose to 13.0 kWh when using the 120V home charge cord that comes in the Volt's trunk.

 

[evnow]

It definitely is. At 10.1 kW / 45 mph they get 9.4 kWh out of the battery, at 17.5 kW / 60 mph they get 9.0 kWh out of the battery and at 22.5 kW / 70 mph they get 8.9 kWh out of the battery.

This is a good reminder to everyone - higher speeds not only increase air resistance - but also battery internal resistance.

 

[Volt3939]

...

Their energy from the wall to charge the battery seems low, though, at 11.1-11.3 kWh. Don't most Volt owners report around 13 kWh from the wall to recharge? ...

Sounds about right for a 2011 Volt, 2013 would be 12-12.5 or so. It all depends on temperature anyway. Charging immediately after driving will use more power to keep the warm battery at temp than charging later after the battery has cooled down. I assume the charging test was conducted at a standard temp, so may look like it's less than an uncontrolled mag review type test where temps were not considered.

 

[qwk]

Then by your judgment, the BMW i3 with Rex cannot be correctly termed an EV, or even correctly termed an Electric car with a gasoline-powered range extender. WHat is it, then? Are you going to call BMW a liar if they refer to the i3 Rex as an EV with extended range?

This is really simple to understand unless one has an agenda.

EV's don't have tailpipes. If it has a tailpipe, its a hybrid.

 

[edatoakrun]

Notice that when "new" (~8,000 miles) this Volt's discharge efficiency is considerably lower at higher kW, resulting in discharge efficiency of only ~92% (as gauged by recharge capacity) resulting in range of only ~ 27.4 miles, in the 70 mph constant speed test.

Does that range at ~70 mph (at all the other controlled test variables) sound about right to the Volt drivers?

This is from last Saturday 10Aug2013 and I was driving 70 mph following a friend up to a MI lake. 39.6 EV miles with ECO A/C on.

Since those results are so far out of line with all credible test data, all that would suggest to me, is that you did not accurately replicate the test variables, and/or that Volts may have a "gauge problem" resulting in inaccurate dash data, just like LEAFs do.

.... At least they appear to be consistent - their LEAF testing also shows lower range than what most would expect.

IMO, if you want accurate range/capacity data, look at the (hopefully) impartial and competent results from the professionals.

If we just look at the DOE test data, rather than the "expectations" of Volt and (present or former) LEAF drivers, we do see some interesting results, when comparing a ~14 (?) month old LEAF with ~7,000 miles, and a ~6 month old (?) Volt with ~8,000 miles.

It looks to me that the LEAF slightly outperformed the Volt in efficiency "from the wall" at all three speeds, 45, 60 , and 70 mph, with lower Wh/m used, when tested at similar ambient (the being Volt's slightly lower) and very similar battery temperatures.

Even at 70mph, when the Volt's reduced drag would be expected to put it ahead, it's lower efficiency at the higher kW battery discharge put the LEAF ahead by a nose:

LEAF: 52.8 miles at 70 mph constant using ~21.3 kW from the EVSE to recharge, 403 Wh/m AC.

http://avt.inel.gov/pdf/fsev/fact2011nissanleaf.pdf" onclick="window.open(this.href);return false;

Volt: 27.4 miles at 70 mph constant using ~11.2 kW from the EVSE to recharge, 409 Wh/m AC.

http://avt.inel.gov/pdf/EREV/fact2011chevroletvolt.pdf" onclick="window.open(this.href);return false;

In retrospect, I guess that we should have expected the lower kWh Volt battery to function at reduced efficiency at similar charge and discharge rates, than the higher kWh battery in the LEAF. Notice the Volt recharges much more slowly at L2 than the LEAF per kWh as well, perhaps due to the charge efficiency limitations of the smaller battery?

But you have to wonder, if the Volt's charge/discharge efficiency declines as rapidly as these tests seem to show, what will the Volt's performance in both efficiency and range at higher kW/speeds look like in a few more years?

Again, these tests were before the Volt's more recent tests, which seem to show only slight degredation in total battery capacity, but much higher resistance and lower efficiency in charging and discharging than in the test above, resulting in a considerable loss of kWh available to use on the road.

I'm looking forward to seeing how the 2011 LEAF compares to the Volt, when the DOE publishes its updated (BOT VS EOT) results.

 

[RegGuheert]

Remember the capacity test you are discussing was at ~15.25 kW, which occurs at what, about 55mph level speed?

Yes. I'm sure they chose 15.25 kW as the one-hour discharge rate, which is an appropriate rate for the Chevy Volt, IMO.

The available (DC from the battery) capacity could be higher at higher discharge efficiency, at lower kW.

That is axiomatic for batteries, as far as I am concerned. That is why one cannot reconcile the 15.2 kWh capacity from the "Static Capacity Test" shown in Table 1 with the 15.53 kWh one-hour discharge rate capacity shown in Table 3. I do not trust Table 1 since it indicates a 5% capacity drop within the first 8478 miles but only a 2% drop over the next 14,836 miles. No explanation of that table is given. It is my estimation that Table 1 may have been fabricated to support the (foregone) conclusion provided in the report.

The rest of the data you have reported is from testing the battery operating under the control of the Volt's BMS, which does not give a transparent view of the battery performance, only what is made available to the user.

One additional note: As the battery in the Chevy Volt degrades, the BMS will release more and more of the capacity of the battery, likely at both ends of the SOC range. What that means is that the drivetrain will operate at higher (static) voltages at the beginning of battery discharge and at lower voltages at the end of discharge. If you combine this with the higher resistances reported in the battery test, at normal load levels you likely will find that the drivetrain operates at lower voltages over the entire discharge curve than when new. This could lower the efficiency of the drivetrain as the battery degrades, meaning both the battery AND the drivetrain lose efficiency as the vehicle ages. (The same concept also applies to the LEAF.)

As an HCH owner, I find it interesting that the Chevy Volt battery deterioration is likely to show itself to the owner around the same point where HCH owners saw it: 100,000 miles (assuming my earlier estimations are accurate). And please don't get me wrong, I would consider this an outstanding result! We still love our HCH, even after 11.5 years and 91,000 miles. I drove 220 miles on a mostly 70 MPH highway with a 500-foot elevation gain on Saturdaatone achieved 56.0 MPG in our 2003 HCH. This is with a degraded battery and the new restricted SOC range as reprogrammed by Honda. This is a better result than previously achieved. Methinks my LEAF experience has improved my hypermiling skills!

 

[surfingslovak]

Why would a 15.25 kW static-load discharge test be appropriate? Reason I'm asking: Nissan used a 5 kW static-load discharge test on the Casa Grande cars last year; there does not seem to be a common standard or agreement. Given the aerodynamics of the Volt, 15.25 kW should be close to steady 100 km/h (62.5 mph). In terms of internal resistance increase, I would have a look at the number of cycles as well as the effective battery temperature. Since the chemistries are comparable, albeit from different manufacturers and with materials from different suppliers, we should see a similar internal resistance increase in the LEAF, all other things being equal. This could also potentially help explain the lower than anticipated energy economy readings, since the cars were not factory new at the beginning of the test; they have been purposefully placed in service prior to initial evaluation.

 

[RegGuheert]

Why would a 15.25 kW static-load discharge test be appropriate?

Because I feel that is close to power level that many will use when driving the Volt AND it corresponds to an industry-standard test approach: discharge at C. At 15.25 kW, you should be able to drive a new 2011 Volt for about 41 minutes given the 10.5 kWh available. If it only consumed that much power at 100 km/h, then you should be able to drive 41 miles on the highway at that speed. I suspect 55 MPH is closer to the right speed.

Reason I'm asking: Nissan used a 5 kW static-load discharge test on the Casa Grande cars last year; there does not seem to be a common standard or agreement.

5 kW is too low for the LEAF, even if it corresponds to the LA4 range that the LEAF achieves. IMO, the LEAF battery should also be discharged at about 15 kW for measuring capacity. That would correspond to a similar 55 MPH and would equate to about 1 hour 24 minutes of driving given the 21 kWh available. At 55 MPH, that would correspond to driving 77 miles.

Since this is how these vehicles are typically used, I think it is reasonable to test capacity at that power level. In this way, the resistance of the battery is included in battery capacity calculations.

 

[surfingslovak]

Since this is how these vehicles are typically used, I think it is reasonable to test capacity at that power level. In this way, the resistance of the battery is included in battery capacity calculations.

Certainly, but this does not address the fundamental question why an auto manufacturer can use one type of load in their testing and modeling and the NREL lab another. It would be good to have comparable metrics, which would help avoid the type of disputes seen here and elsewhere. Remember the reaction from Phoenix owners when they were essentially told that they drove their LEAFs too fast and too much? Although the press release was worded more carefully, I think it was an indirect acknowledgement that Nissan tests and models battery life using lower loads and fewer cycles. I'm not sure what GM or BMW might be using internally, and what type of average static load the new EPA test cycle would translate to. I think that these are all valid considerations to get accurate apples-to-apples comparisons, given how much internal resistance plays into this and how it changes over time.

 

[RegGuheert]

Certainly, but this does not address the fundamental question why an auto manufacturer can use one type of load in their testing and modeling and the NREL lab another.

I would like to think that NREL would perform this type of testing independently of the manufacturers in order to get some semblance of unbiased information out to the public. Unfortunately, the NREL conclusions and Table 1 make me wonder if there is a political agenda involved in this report.

It would be good to have comparable metrics, which would help avoid the type of disputes seen here and elsewhere. Remember the reaction from Phoenix owners when they were essentially told that they drove their LEAFs too fast and too much? Although the press release was worded more carefully, I think it was an indirect acknowledgement that Nissan tests and models battery life using lower loads and fewer cycles. I'm not sure what GM or BMW might be using internally, and what type of average static load the new EPA test cycle would translate to.

Frankly, I wish Nissan would forget all about the LA4 driving cycle and would discuss more relevant driving cycles. My opinion is that LA4 has permeated their corporate culture to the point that they actually believe their EVs have the range predicted by that drive cycle. I have no idea what the other manufacturer's use for their references. EPA is a step in the right direction, but it could use some improvements, also.

I think that these are all valid considerations to get accurate apples-to-apples comparisons, given how much internal resistance plays into this and how it changes over time.

Agreed, but note that my recent posts in this thread were not trying to make an apples-to-apples comparison between vehicles. Rather, I was trying to use the little bit of battery data for the Volt from NREL to try to predict users' future battery aging expeiences. For this purpose, I think the C-rate discharge capacities are the most appropriate ones to use.

 

[surfingslovak]

Agreed, but note that my recent posts in this thread were not trying to make an apples-to-apples comparison between vehicles. Rather, I was trying to use the little bit of battery data for the Volt from NREL to try to predict users' future battery aging expeiences. For this purpose, I think the C-rate discharge capacities are the most appropriate ones to use.

Understood! That comment was not directed at you

 

[TomT]

Bingo!

EV's don't have tailpipes. If it has a tailpipe, its a hybrid.