[Dayle Frame]

I’ve had my Bolt since Feb, 2017 and it has 74k miles on it. Recently, I took a trip from my home near Lansing, MI to Kansas City and back (1998 mile trip, 544kW used, $85 spent, 42% of miles were free). When I got home, I plugged into my Juice Box and it added 60.85kW to her (I REALLY drained her on the last leg coming home).

I’m trying to figure out what, if any, degradation my battery is seeing. In reading a few threads about it, it appears that I’m not supposed to be able to put that much juice into her after so many miles. As an analytical chemist, math doesn’t scare me but I’ve seen so many formulas, it gets confusing trying to take a deep dive into battery degradation and longevity.

So where do I start? What variables can I monitor so I can get a handle on how to figure out how long this battery pack will last? Normally I’d say "email me offline" but I have to assume there are others who could benefit from public posting of this kind of information. Thanks in advance for the help.

Dayle

 

[davioh2001]

Dayle, remember if the juice box reported 60.58 that's the electricity being used during that session some of it is wasted as heat due to imperfect wiring (no wiring is going to have perfect 0 resistance). The only real way of knowing your capacity is to run Your bolt completely flat run the HVAC in the driveway when You are near 0 and look carefully at the energy use screen to see if it makes it all the way to 60.0 kwh used since last full charge. If that is the case, congratulations You have 0% degredation.

 

[The Other Tom]

Generally battery temp and number of full charges determine how long a battery will last. Torque Pro will help you monitor your battery. Also do a search for FCE (Full Cycle Equivalent).

 

[Dayle Frame]

Thanks for the guidance.

The night I added the 60.58kW, it was soooo low that I wasn’t aware enough to check that. The next time I’m that close to the edge, I’ll remember to check that. There have been times when I’ve put more current into the car but that’s been in the dead of winter when it’s been REALLY cold (in uninsulated garage).

Dayle

 

[Pike Bishop]

Good morning Dayle,

I have also been asking questions to try to understand what 'rituals' we do with our EVs make sense and what are just myths (e.g.-I don't DCFC unless the day is a prime number...) I found a thesis paper and an IEEE journal article that seem to give some information. I am a physicist and not a chemist, so your read would be welcome.

By Dr. Bolun Xu, MIT and ETH Zurich
https://ethz.ch/content/dam/ethz/sp...ystems-dam/documents/SAMA/2013/Xu-MA-2013.pdf

(PDF) Modeling of Lithium-Ion Battery Degradation for Cell Life Assessment

PDF | Rechargeable lithium-ion batteries are promising candidates for building grid-level storage systems because of their high energy and power... | Find, read and cite all the research you need on ResearchGate

www.researchgate.net

Xu et. al. chose as their basis Li-ion cells used in grid stabilization. These have similar use characteristics to EV batteries in that each battery sees regular cycles with somewhat random discharge depth. The BOLT EV battery is similar because it sees daily use but can use more or less energy during the cycle depending on external factors such as weather, traffic, and extra miles due to special trips.

Their model 'fits' based on three large factors:

• Calendar aging -- Just time in service
• Cycle aging -- Number of charge-discharge cycles
• Stress aging -- Environmental or external factors (modeled as Arrhenius activation)

The general curve looks like this:

Batteries lose some capacity at beginning of life due to electrolyte film formation at (A), then experience slower calendar and stress degradation at (B) and (C), followed by electrolyte film cracking and breakdown at (D). The cycle scale could be on the order of 10,000 cycles, or about 30 years of daily EV use.

What I am able to make out dispels some myths:

DCFC does not add to degradation with a properly designed battery management system. Essentially, the authors argue the charge rate is controlled by the designers and should be placed in a safe operating zone for minimal degradation. GM designed the BOLT EV to charge up to 55kW in small range of SOC; that should be safe for their life estimates.

There are some things we seem to get right:

• Maximum SOC is important. Charging to 80% is better than 100%. Again, the difference is seen over thousands of cycles.
  
  
• Temperature is important, both for calendar degradation and cycle count degradation.
  
  
• SOC operating range is important. If you can drive between 50-80% SOC, that's better than 20-90%. Again, a few percent difference over thousands of cycles.

And some interesting surprises

Depth of Discharge (DoD) is critical and can cut battery cycle life by a factor of four if constantly repeated. A model battery may have a 20,000 cycle life discharging 40% regularly and only 5,000 cycles discharging >95%. This condition may be an issue with drivers who adopt a 'gasoline' fueling model: run to near empty then hit the DCFC. Remember, this is not going to happen with one long drive; 5,000 daily cycles is well over 15 years.

I enjoyed the read and hopefully you can add to the forum.

 

[Eriamjh1138]

The onboard charger is not 100% efficient.
Balancing cells use energy also.

 

[p7wang]

In other posts, there was a mention of charging being about 85% efficient on either L1 and just a tad better in L2. So it would take about 70KWh to charge 60KWh.

 

[ArizonaJon]

Thanks for the link. I just glanced at the article. I may spend some time trying to understand it later. Too much calculus.

But, the charts on page 29 are very interesting. The only problem is we do not know what the true formulation of our Bolt batteries, but I feel confident they are not the same as in the study. But I bet GM has the data. I wish they would publish it instead of keeping it a company secret. I believe the article was published in 2016. So it would have been based on a battery technology from a few year before that.

 

[Vertiformed]

@p7wang, in my experience, charging can be considerably more than 85% efficient. Exactly how efficient it is depends on various factors (e.g., whether battery needs cooling afterwards, longer charges are more efficient than short ones, etc.).

As one data point, yesterday, I drove 68 miles and the Bolt said it used 16.7 kWh (which is 4.07 miles/kWh, not bad for running the AC the whole time and it even being hot enough to do a little battery conditioning), but my JuiceBox tells me it added 17.94 kWh over 2.5 hours. So from that I know that charging was about 93% efficient, at an average rate of 7.18 kW. I can also calculate the MPGe as 68/(17.94/33.7) = 127.74 MPGe.

 

[Vertiformed]

@Dayle Frame, there are lots of papers out there that are interesting, but you won't find anything definitive for the actual batteries in the Bolt. Even when you find papers on the actual base chemistry of the Bolt's battery (NMC 622) it'll be a baseline. Actual real-world batteries have proprietary additives that make significant improvements to their performance.

Various external factors influence performance, including temperature, discharge rate, and discharge depth and charge/discharge pattern. These factors both influence battery life overall and performance in the moment.

Pretty much no Bolt owner is willing or able to do the kind of careful controlled tests necessary. No one has even shown that the usage numbers reported by the Bolt are actually accurate.

And even if you did know, it's not sure how useful it is anyway. All sorts of factors influence the viability of a trip. Suppose, for example, your battery hasn't degraded at all, but it's pretty cold and you have a headwind.

From following various Bolt forums, what I've seen is that there have been some Bolts that had bad cells in their batteries due to a manufacturing defect, but other than those cases, the pretty much universal experience with Bolts is that degradation is negligible. Based on the science, papers often show batteries (with 1C discharge rate and no proprietary additives) showing clear signs of degradation at about 1000 cycles. But a thousand full-charge-equivalent cycles in a Bolt is 238,000 miles of EPA range — 100,000 miles of EPA range is only 420 cycles.

The fact that trying to measure Bolt battery degradation is so ambiguous and error-prone is in stark contrast to the Nissan Leaf, where drivers had pretty obvious battery issues, even non-tech-savvy ones who weren't out to over-analyse.

 

[Dayle Frame]

Over analysis is what we chemists do. ?

The reason I started this thread is because I got less mileage than I expected while on the KC trip. And as I was schlepping around friends who hadn’t seen an electric car, I had to answer non stop questions about the whole gamish (cost, range, charging, battery life, etc.).

Virtually everywhere I charged, I used a DCFC. At home I have a plain old juice box. I was curious about whether that was a factor in my mileage. In hindsight, I doubt it.

I’ll read the paper and see what I can glean from it but I encourage others to chime in as well.

Dayle

 

[Vertiformed]

When people ask you about your car's battery and how long it will last, you might want to ask them about their catalytic converter and how long it will last. Catalytic converters degrade over time, and this degradation can affect fuel economy and thus vehicle range. It is also a pretty expensive part to replace, and can even be damaged by something as simple as poor fuel quality or bottoming out the vehicle in the wrong way.

If the answer is that it isn't something they usually think about (because it's typically designed to last at least 100,000 miles), you could tell them that the Bolt's battery is similar.

That's not to say that it doesn't age, but the designers of the Bolt deliberately made the car such that owners don't really need to worry about looking after the battery any more than they worried about looking after the catalytic converter in their ICE vehicle.

 

[cwerdna]

The night I added the 60.58kW, it was soooo low that I wasn’t aware enough to check that.

Dayle, can you please get the units right? I believe you meant kWh here and in your OP. Please see https://www.mynissanleaf.com/viewtopic.php?p=520169#p520169.

The onboard charger is not 100% efficient.

Yep. If one opens the hood after L1 or L2 charging for awhile, the on-board charger will be warm. The OBC is one of the source of losses. There's also fixed overhead of running pumps when AC charging. If the battery thermal management kicks in, there's overheard from that (e.g. pumps and AC compressor).

Not all the energy coming out of the wall gets added to the battery as useful energy.

 

[hickman55]

Thanks for the guidance.

The night I added the 60.58kW, it was soooo low that I wasn’t aware enough to check that. The next time I’m that close to the edge, I’ll remember to check that. There have been times when I’ve put more current into the car but that’s been in the dead of winter when it’s been REALLY cold (in uninsulated garage).

Dayle

My Juicebox has Pro40 has a web screen that shows both the energy used by the EVSE (from the meter -highlighted) and the energy put in the battery (circled in red). The documentation indicates that the EVSE is ~ 92% efficient, so it's possible that the your battery took 92% of the 60.85 (55.98kWh) which would seen reasonable.

 

[cwerdna]

JuiceBox is just making an estimate. There's nothing in the J1772 protocol for the attached vehicle to tell the EVSE how much actually got added to the battery.

https://openev.freshdesk.com/support/solutions/articles/6000052074-basics-of-sae-j1772 has primer.

That said, ~90% efficiency at 240 volts is probably within the ballpark.

Govt labs had done some testing that included OBC efficiency but it's possible the lab/efforts are now dead. Examples at https://web.archive.org/web/20160310073446/http://avt.inel.gov/fsev.shtml. Search for steady state. There are at least 3 reports on this: for i3 and 2 different model years of Leaf. OBC on '11 and '12 Leafs is a totally different part than the ones on '13+ Leafs.

edit: I found a new table of contents page at https://avt.inl.gov/content/charging-system-testing/vehicle-charging-system-testing but it looks like there hasn't been any new work done on this topic for awhile.

 

[One1whaoo.]

There have been times when I’ve put more current into the car but that’s been in the dead of winter when it’s been REALLY cold (in uninsulated garage).
Dayle

In winter, you are also consuming power to heat the battery, as well as charging it.

 

[psyflyjohn]

Dayle, remember if the juice box reported 60.58 that's the electricity being used during that session some of it is wasted as heat due to imperfect wiring (no wiring is going to have perfect 0 resistance). The only real way of knowing your capacity is to run Your bolt completely flat run the HVAC in the driveway when You are near 0 and look carefully at the energy use screen to see if it makes it all the way to 60.0 kwh used since last full charge. If that is the case, congratulations You have 0% degredation.

By running the battery to zero, you have contributed to the degradation. A catch 22...

 

[raitchison]

By running the battery to zero, you have contributed to the degradation. A catch 22...

I'm more paranoid than most when it comes to battery degradation but even I think the occasional discharge to 0% (or thereabouts) or the occasional charge to 100% won't be noticeable.

 

[davioh2001]

By running the battery to zero, you have contributed to the degradation. A catch 22...

Well this would be in an instance when it read close to 0 and he was home from a long road trip and it read "Low battery" on GOM no longer even displaying any # of miles left. Would the difference running it once down to 2% left to 0% left really make any material difference?

 

[Dayle Frame]

To recreate the experiment, I ran the car around town for several days without charging at night (my normal SOP). I made 285.3 miles on 56.2kW (5.1m/kW and the average temp was in the 70’s). The range read 3 miles when I dared go no further. The JuiceBox says it took 59.993 kWh to stuff 56kW into her. To be able to still use ~56.5kW of the 60kW battery seems pretty good.....to me anyway. That’s 94.2%.

Armed with the comments in this thread, the paper I still need to read and the data I’ve gathered, I’m willing to put this to bed......for now. I think I’ll try seeing how far down I can take her every quarter or so and see what the long term data tells me. Stay tuned.

Thanks for all the input folks.

Dayle