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Discussion Starter #1 (Edited)
I was asking myslef the question whether a partial discharge and recharge has the same effect as a full discharge. I googled it. Here is one page:

http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

So what its saying is charge more often as soon as you can and the battery will last longer. which means plugging it in every night is a good thing. Dont wait until the tank is empty like an ice car.

Which plays into my thought during winter to plug it in every night (level 2) so battery conditioning does not take away from battery power and morning preconditioning will use shore power to do this and also not take it from the battery. Plus I get a warm cabin :) which when warm take much less energy to keep warm.

Thoughts?

From this page
"Most Li-ions charge to 4.20V/cell, and every reduction in peak charge voltage of 0.10V/cell is said to double the cycle life. For example, a lithium-ion cell charged to 4.20V/cell typically delivers 300–500 cycles. If charged to only 4.10V/cell, the life can be prolonged to 600–1,000 cycles; 4.0V/cell should deliver 1,200–2,000 and 3.90V/cell should provide 2,400–4,000 cycles."

AND finally the MILLION DOLLAR QUESTION:

How is chevy handling the charge? Are they pushing the battery to 100% if it actual cell capacity.
 

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Discussion Starter #2 (Edited)
I think I may have answered it.
If GM states 238 miles per charge and have a 100,000 mile warranty then that would be 420 charges total. Right in the wheelhouse but at that point your range should theoretically be close to dead. That would maybe cause a warranty claim.
Maybe I did not answer it???

Anyone know the exact details on the battery warranty down the road? How they determine replacement?
 

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I think the link is for lithium batteries in consumer electronics, such as lithium polymer. There are a **zillion** different variants of Lithium battery with many different electrode materials....all they have in common is that Li ions are the charge carrier.

GM and LG have not released a lot of details about the chemistry of the Bolt battery (that I could find)...but the wiki page describes it as a 'Nickel rich' chemistry optimized for high temperature durability.

This means that it is probably a Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2 or NMC) type, with a prismatic (flat) cell geometry...similar to many other EVs on the market (like the LEAF).

Tesla and the Chinese makers use different chemistries. Tesla's is more flammable, and requires a special pack design to limit fire spread in case of cell failure (separate cylindrical cells with fire retardant foam spacers). The Chinese makers (e.g. BYD) favor LiFePo batteries that are much more durable (cycle wise) and low flammability at the cost of some other performance metrics. This is well suited to use as taxis and things with a rather small/cheap pack and small AER.

Overall, I think you are worrying too much reading this stuff. The LEAF, without active cooling, has a 80k mile warranty, which given the 107 mile range works out to 750 cycles. The Bolt battery is 2x the size, so it should be good for 160k miles without thermal management....with thermal management it should do well better than that.

To summarize, with current chemistry limitations, EVs with 25-35 kWh packs will last a reasonable time...80k miles warranty, probably useable (with degraded range) to 50-100% longer than that...120-160k miles.

Cars like the Bolt or Tesla with bigger (60+kWh) packs...their batteries are likely to last more miles than the engine in an ICE car, 200+k miles.

Why not give a 250k mile battery warranty? Because they don't have to. 100k is enough to assuage people's fears. Tesla gives an infinite mile battery warranty. And the Bolt system is likely just as well engineered as the Tesla...I think the wheels will fall off first.
 

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Discussion Starter #6
I think the link is for lithium batteries in consumer electronics, such as lithium polymer. There are a **zillion** different variants of Lithium battery with many different electrode materials....all they have in common is that Li ions are the charge carrier.

GM and LG have not released a lot of details about the chemistry of the Bolt battery (that I could find)...but the wiki page describes it as a 'Nickel rich' chemistry optimized for high temperature durability.

This means that it is probably a Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2 or NMC) type, with a prismatic (flat) cell geometry...similar to many other EVs on the market (like the LEAF).
Yeah I saw that but in one chart they compare two batteries NMC being the first, lower, in cycles.

I think the real takaway to me was charge often and less is better. But topping up is the most controversial subject depending on the ability of the management system and programming into thats system as to whether let say the full charge puts a NMC battery to 4.20 volts or as the article say 4.1 volts which would esssentially double its number of full charges.

I am wondering whethe odb2 can see battery voltage and if we observe this based on the cell configuration whether we can calculate what the full charge voltage is.

As with all of these discussions is, is what practises are the best at promoting battery longevity.
 

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I recall another thread that theorized battery longevity would be increased if the Bolt's batteries are ordinarily only charged up to the Hill Top level (80% of full capacity charge?), and only charging to full capacity when driving range is an issue.
 

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People extrapolate way too much from testing articles on sites like BU.
They often test small button type cells or single cell phone pouches with no thermal management, little to no BMS intervention, and chemistries tweaked for a different application than EV's. And then they do repeated full charge/full discharge cycles at a 1C rate (this would be 60 kW charging and discharging on the Bolt) to test the battery. While some data may be relevant and have application to EV battery packs, the degree is questionable.

As to cell voltage, most reports have the LG cells used in the Bolt as specced at either 3.7 or 3.75 volts to achieve the rated capacity. The EPA data submitted by GM shows the Bolt pack as 350V and 171.4 Ah. Since we know the pack is 96s 3p, that gives a nominal cell voltage of ~3.64 V.

All this needs to be taken with a grain of salt however.
The GM data provided to the EPA for the Volt is 337 V and 52 Ah (equals a capacity of 17.5 kWh). The specs on the Gen 2 pack from GM show 360 V nominal (395 V peak) and 18.4 kWh Total Energy with 14.0 kWh Usable Energy.

Links:
http://www.fueleconomy.gov/feg/epadata/18data.zip
https://media.gm.com/content/dam/Media/microsites/product/Volt_2016/doc/VOLT_BATTERY.pdf

Conclusion- draw your own, but look at how and what they are actually testing.

Here is one that uses an emulator to test packs in a closer simulation to real world use:
https://ecpowergroup.com/wp-content/uploads/2013/10/Battery-pack-system-interaction-with-aging-under-real-world-drive-cycle.pdf
It would be easy to pull the graphs from this report and proclaim that any EV in Pheonix, AZ would show ~14% degradation over 1000 cycles while one in Portland, ME would only show ~4%.

Anyone care to actually read the report and point out things that might make this different for the Bolt and/or real world conditions?
 

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Opinion: Over time, Bolt EV’s battery pack behaves pretty much like a typical LI battery.

Here’s why I’ve drawn that conclusion:

I trust GM engineering. They’ve historically been the core strength of GM. The fact they’ve set the ``hilltop reserve`` level of charge somewhere in range of 88 to 90 percent is telling. That ~ 89% hilltop level of charge seems to be much too low. That is, if the goal is merely to allow regen energy to be captured to the battery when it’s owner sets out at the top of a hill.

Assume:
1. 89% charge leaves around 6.6 kWh of unused “space” in the battery ?
2. 9° downslope @ steady 50 km/h ~30 mph provides 10kW’s regeneration
3. My Bolt EV captures regen energy nicely with battery as full as 99.7% of the 60 kWh battery capacity
4. In order to “regenerate” a total of 6.6 kWh going down that 9° hill at a steady 60 km/h, I’d have to drive for 40 minutes (6.6 kWh / 10 kW * 60 mins per hour) under those conditions ! Covering 40 kilometres ~25 miles in doing that !

Whaaaa? Does GM Engineering think that those Bolt EV owners who live on top of a hill, will each have a trip down similar to going down Haleakalā on Maui ? Surely there’s got to be some something wrong with above assumptions ?

BUT in trusting GM engineering in view of their ~89%. I think in truth they`re telling me either 1.) my battery is going to be more durable if I refrain from charging it all the way up all of the time, and/or 2.) they're suggesting please don't always energize the battery to it’s full capacity, in view of the higher warranty cost that may result...for reasons only they can describe.

This also has implication for lessees. If I was leasing with intent to ditch the vehicle in 3-years or so, I’d certainly fill-‘er-up every time.

But since I plan to own my Bolt EV for a long time I’m leaning towards more conservative battery charging habits. Because for reasoning as stated above, I believe the Bolt EV’s battery pack behaves like a typical LI battery: treat it nicely and in the long term, it will give you more cycles and more powerful cycles !
 

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Opinion: Over time, Bolt EV’s battery pack behaves pretty much like a typical LI battery.

Here’s why I’ve drawn that conclusion:

I trust GM engineering. They’ve historically been the core strength of GM. The fact they’ve set the ``hilltop reserve`` level of charge somewhere in range of 88 to 90 percent is telling. That ~ 89% hilltop level of charge seems to be much too low. That is, if the goal is merely to allow regen energy to be captured to the battery when it’s owner sets out at the top of a hill.

Assume:
1. 89% charge leaves around 6.6 kWh of unused “space” in the battery ?
2. 9° downslope @ steady 50 km/h ~30 mph provides 10kW’s regeneration
3. My Bolt EV captures regen energy nicely with battery as full as 99.7% of the 60 kWh battery capacity
4. In order to “regenerate” a total of 6.6 kWh going down that 9° hill at a steady 60 km/h, I’d have to drive for 40 minutes (6.6 kWh / 10 kW * 60 mins per hour) under those conditions ! Covering 40 kilometres ~25 miles in doing that !

Whaaaa? Does GM Engineering think that those Bolt EV owners who live on top of a hill, will each have a trip down similar to going down Haleakalā on Maui ? Surely there’s got to be some something wrong with above assumptions ?

BUT in trusting GM engineering in view of their ~89%. I think in truth they`re telling me either 1.) my battery is going to be more durable if I refrain from charging it all the way up all of the time, and/or 2.) they're suggesting please don't always energize the battery to it’s full capacity, in view of the higher warranty cost that may result...for reasons only they can describe.

This also has implication for lessees. If I was leasing with intent to ditch the vehicle in 3-years or so, I’d certainly fill-‘er-up every time.

But since I plan to own my Bolt EV for a long time I’m leaning towards more conservative battery charging habits. Because for reasoning as stated above, I believe the Bolt EV’s battery pack behaves like a typical LI battery: treat it nicely and in the long term, it will give you more cycles and more powerful cycles !
All of this completely ignores the effect of temperature (both on battery capacity and for the need for heat - battery and occupants). Run this model again for someone living in a climate where they start their morning trip at or below freezing. You are also assuming 100% efficiency from the generation making it into the battery. Someone living is Estes Park, Colorado and commuting to Loveland would have a 30 mile (48 km) commute that loses 2500+ feet (760+ meters) in altitude. And could start at -25 F (-30 C) or colder. Extreme? Perhaps, but why choose a token hilltop reserve (2%?) when someone needing nearly all the range available with hilltop reserve will choose a full charge anyway?

You won't hurt the battery by not charging to 100%, but the BU articles that are often quoted are not studies that can be directly applied to the Bolt (or any EV).

I am not arguing that the Bolt will not suffer from additional degradation if charged to full every night. Only that the data is not available to conclusively prove it.
 

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I do agree that the 90% hilltop reserve number seems to leave an excessive gap. I start every drive with 750 ft descent over 2 miles. Given the anomalies of some of the screens, I do want to know how much I am gaining. It is pretty consistent at 0.6 kWh. As noted that is about 10% of the 6 kWh that have been left in reserve for me. So it is odd, but whatever: I can live with it and will use it, but must remember to charge to full before any trip of 150 miles or more.

And I note that 0.6 kWh is 2.4 miles at normal flat driving. So my 2 mile descent gains me 2+ miles flat. Meaningless, I know.
 

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I do agree that the 90% hilltop reserve number seems to leave an excessive gap. I start every drive with 750 ft descent over 2 miles. Given the anomalies of some of the screens, I do want to know how much I am gaining. It is pretty consistent at 0.6 kWh. As noted that is about 10% of the 6 kWh that have been left in reserve for me. So it is odd, but whatever: I can live with it and will use it, but must remember to charge to full before any trip of 150 miles or more.

And I note that 0.6 kWh is 2.4 miles at normal flat driving. So my 2 mile descent gains me 2+ miles flat. Meaningless, I know.
So a 750 foot drop over a 10,560 foot run (2 miles * 5,280 ft/mi) gives an average slope of 7.1% or 4-degrees. That’s not very steep ? Can it be travelled at an average speed of 50 mph ?

Because, my estimate of the constant speed on flat terrain in order to get 4 miles/kWh (from your 2.4 mi using 0.6 kW) is 50 mph.

Now all that’s needed is: how many kWh is used to ascend that same 2-mile hill at an average speed of 50 mph ?

Then one could calculate the efficiency of regeneration in that circumstance. In order to test the hypothesis: how close is it to 70%?
 

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I did that test and reported on my results here. I found that regen appeared to be roughly around 68% efficient, so I figure on being able to recoup around 2/3 of the energy.
Yes I read that thread and trust the 2/3 is about right. But I don't recall seeing actual test data & assumptions. So that's what I'm looking for from stanwagon. I don't have any good hills locally where I could safely do the test myself.
 

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Discussion Starter #15
As far as regen in concerned my opinion is its 90% efficient (as the motor is that) . It that GM most likely manages the regen and limits it at times for battery longevity. Especially at the top of the battery charge, it just cant pile a ton of amps into the battery during top off. A little simple answer but I think one can understand.
 

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What information about my methodology and results did I not explain in that post?
Thanks a lot for requiring me to take time to hunt for that post. It’s here #39 out of 43 posts:

http://www.chevybolt.org/forum/10-technical-discussion/9354-how-efficient-bolt-regen-4.html

I agree it was sufficient in order to get a rough estimate. And if I’d ever heard of Cypress Bowl I may have had a better appreciation of what was involved.

But it lacks “colour” and therefore it’s not as convincing : length of the incline, length of the “run” horizontally, vertical drop, grade of the incline, vehicle speed, was run down in L or D with paddle, what were kWh snapshots at the specific key points (and not just spot kW observations) other road surface conditions weather conditions ambient temperature and so on.

stanwagon obviously enjoys his mathematics and has ready access to what appears to be a nice test site. I’m looking forward to his data and conclusions.
 

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Regen has to make two trips through the drive train...the kinetic energy of the vehicle is less than originally in the battery, and then it has to be recovered back into the battery by the drivetrain.

Sqrt(0.68) = 0.824 or 82.4% efficiency for a single pass through the drivetrain, including motor efficiency, power electronics, battery round-trip losses and good ol mechanical friction.

Twice. Makes 68%.....which is about the same figure on all other BEVs tested.
 

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Regen has to make two trips through the drive train...the kinetic energy of the vehicle is less than originally in the battery, and then it has to be recovered back into the battery by the drivetrain.

Sqrt(0.68) = 0.824 or 82.4% efficiency for a single pass through the drivetrain, including motor efficiency, power electronics, battery round-trip losses and good ol mechanical friction.

Twice. Makes 68%.....which is about the same figure on all other BEVs tested.
Hmm. Nice rule of thumb but how does it explain the drastic difference in regen deceleration force and energy capture, between Bolt and Model 3 ?

Give me experimental results please.
 

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I don't have any data....but I've read posts by others on multiple fora with multiple EVs...and they all come in somewhere in the 60s. And I don't see how that can be much improved, given the 'round-trip' math above.
 
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