90% Charge (Better for the HVB) vs 80% charge (more economical)

ChasingCoral

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As the battery's state of charge increases, so does the it's resistance; therefore, it takes more energy to charge a battery when it is nearly full.
Theoretically, yes but practically this should not be the case over most of the Mach E battery pack range. Modern lithium cells equipped with liquid-cooled battery management systems are far more complicated. They are designed to keep reduce resistance by removing heat produced. We'll know for sure once we have thoroughly examined Mach E battery charging curves.

You are absolutely correct about it costing more to charge from 80-90% than from 70-80%. Several people stated otherwise, but I'm quite sure they were simply guessing.
I believe you are guessing. Can you back up your absolute statements with data showing that there is a significant increase in energy requirement from 80-90% than from 70-80%?

Wow... That's really great your vehicle does this well with the charging curve, but there are probably subtle changes you aren't noticing as it's not physically possible for the charging efficiency to decrease over time.

Here is a graph for a Nissan Leaf on a level 2 charger which does not do as well as you report with your e golf. 1 hour of charge adds the 1st 40%, but it takes 1.5 hours to add the next 40% to reach a total charge of 80%. This is a more realistic curve shape reflecting decreasing charging efficiency over time.

This is physics. Kind of like gravity... It's there whether you have noticed it with your e golf or not. I suspect if you created a graph with as many data points as this you would be surprised. I suspect you just haven't noticed the change over time because you are either "eyeballing" it or using approximations when monitoring the charging data. If you kept precise data like in this graoh, you would see similar results.

How significant this efficiency drop is to each person is will vary, but there is certainly a cost increase to charging to higher percentages.

Screenshot_20210220-042552.jpg


Some people will drive in an ICE vehicle past a gas station charging $2.75 to reach a station charging $2.74 because they don't want to waste that extra 1¢ per gallon they could otherwise save. Likewise, if the cost of charging increases by any amount over time, some people will find it relevant.

Saving a measly 10 cents every night over the course of a year will save $36.50 over the course of a year. That is like getting a few free "fill ups."
This is a case that actually shows your absolute statement that 80-90% cost more than 70-80% is wrong. There is no appreciable change in the charging rate (energy per time) between 50-60% and 80-90%. However, because of the change from the Leaf's stage 2 to stage 3 charging cycles there is a significant but short-lived drop in charging rate at around 70%. This results in slower charging 70-80% than 80-90%, entirely driven by the operation of the BMS (albeit an air-cooled BMS in the Leaf as compared to the liquid-cooled BMS in the Mach E). Because cost is driven by total electricity used and there are losses from the operation of the charger, it is entirely possible that the EVSE operating cost may actually be greater in this Leaf from 70-80% than 80-90%.

It's the charging resistance which increases as the battery voltage increases. Similar to blowing up a balloon. Getting that last bit of air in is harder. I realize the physics aren't the same in my analogy, but the point stands.
Your analogy is close enough, though. This is why most BEV BMS taper the charging rate significantly at a point somewhere between 90-100% as you see in the Leaf example above, even with L1/L2 charging. This is also why DCFC usually tapers at 80%.

Getting back to the OP's question and your supposition, there is no evidence that charging from 80-90% on L1/L2 chargers is any more expensive than 70-80%. However, in the long-run, limiting charging to 80% unless more is needed has advantages for battery life. Of course, in the Mach E there is a ~11 kWh reserve built into the battery. So in practicality regular charging to 90% is probably not any worse for battery wear than 80%, thus Ford recommends 90% (rather than 100%) to help make sure the battery lives up to its warranty.
 

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Lithium ion batteries do not show an increase in internal resistance as they charge up, as nickel and lead batteries do. In fact it will decrease by 5-10% as the battery charges from 0-70%, flatten out, then increase again as you approach 100% of true SOC.

It is even possible, based on the chemistry for these batteries, to have LESS internal resistance between 80% and 90% than they do between 70% and 80%.

EDIT: To expand on this, the reason for the 80% taper is not internal resistance or heat generation, it is degradation. You can run full charging power (where full is 1C to 0.25C depending the design) into a lithium battery right up until you reach the constant voltage knee around 97% SOC.
 
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timbop

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Lithium ion batteries do not show an increase in internal resistance as they charge up, as nickel and lead batteries do. In fact it will decrease by 5-10% as the battery charges from 0-70%, flatten out, then increase again as you approach 100% of true SOC.

It is even possible, based on the chemistry for these batteries, to have LESS internal resistance between 80% and 90% than they do between 70% and 80%.
Thank you for the correct info.
 

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Lithium ion batteries do not show an increase in internal resistance as they charge up, as nickel and lead batteries do. In fact it will decrease by 5-10% as the battery charges from 0-70%, flatten out, then increase again as you approach 100% of true SOC.

It is even possible, based on the chemistry for these batteries, to have LESS internal resistance between 80% and 90% than they do between 70% and 80%.

EDIT: To expand on this, the reason for the 80% taper is not internal resistance or heat generation, it is degradation. You can run full charging power (where full is 1C to 0.25C depending the design) into a lithium battery right up until you reach the constant voltage knee around 97% SOC.
Since data was asked for earlier, here is a little. I can’t share my own measurements, but this paper on EKF estimation of SOC and pulse measurement of internal resistance has some interesting information and good figures of data from some small cells. The values in the Mach E battery will obviously be different, but the overall trend will be similar.

https://res.mdpi.com/d_attachment/energies/energies-10-01284/article_deploy/energies-10-01284.pdf

For those interpreting the graph, higher Ri (internal resistance) means more losses during charging or discharging. This shows that, for the battery they tested, the most efficient charging occurs between 70 and 90% SOC, at temperatures over 30C.

Of course, degradation isn't shown here, just heat generation. You wouldn't want to charge your batteries at full power at 90% SOC and 30C on a regular basis for that reason.

Ford Mustang Mach-E 90% Charge (Better for the HVB) vs 80% charge (more economical) F2A6A864-FA74-4531-928F-A0EC0761052D
 
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wmaney

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Ford recommends keeping the HVB at 90% charge for the health of the battery. However, it takes more energy (longer time) to charge from 80 to 90% - resulting in a higher cost from your electricity provider. It's my understanding that it's cheaper (and faster) to go from 70 to 80 % charge than it is to go from 80 to 90% charge even though its the same increment (10%). So what is everybody doing or plan on doing - charging to 90% (except for days when a complete charge is needed) or 80%? Thanks
Thank you all for your informative responses - learned a lot - my personal knowledge SOC is approaching 100%! Some of you spent a lot of personal time thinking about this and responding - I (and others I'm sure) appreciated all the effort and the information. Again thanks.
 

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True, which is why I personally will probably always charge to 90 at home.
OK, I let it go this morning, but now you intend to follow the course I suggested - yet you dismissed as chattle. I don't appreciate you calling me a moron and telling me to shut up.

You espoused a vast mathematical analysis and purported expertise. In reality, you manufactured your data to buttress the assertion that there was a significant difference. And yet you intend to do exactly what I suggested and for the same reason - despite your dismissal of my argument. That is disingenuous at best.

In point of fact had you done a QUALITATIVE analysis you would have recognized that the difference is negligible. That is, assuming one is rational enough to admit that the equivalent of a cup of starbucks coffee every other month is neglgible.
 

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For folks who have taken delivery, did you have to set the charging limit to 90% or was that a factory setting?
 

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For folks who have taken delivery, did you have to set the charging limit to 90% or was that a factory setting?
Default is 100% everywhere. You have to actually charge once, and then you can create a profile for the location with the charging level set to less than 100%.
 

machefan

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For folks who have taken delivery, did you have to set the charging limit to 90% or was that a factory setting?
You have to set it. It’s easy to setup and adjust as needed.

Dealer’s PDI says to charge to 100%

Mine was delivered to the dealer full which I wasn’t happy about but nothing I could do.
 

dbsb3233

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A few thoughts - as far as the battery, 80% is better for the battery than 90%, which is better than 100%. It won't matter right away, but it could matter over many years. Either way the holdback on the MachE battery is generous so even a reported 100% is probably more like 92% or 93% of the chemical SOC.

As far as energy required to go from 70-80% and 80-90%, no, both cases will use about the same amount of energy. Internal efficiency of batteries is pretty flat through most of their curve. Where this becomes less true is at the very margin, more like 97% to 100% of real charge (which you can't access on this car anyway).

Faster charging, however, is less efficient than slower charging, since energy losses in the battery are mostly due to ohmic heat generation, and those losses increase with the square of current, so doubling your charge rate is 4 times the lost energy. But again, you don't need to worry that much about it, because the home 240V L2 chargers are still only charging at around 0.15C, which is a very gentle charge rate. You might become concerned about it if your primary every-day charging was on a DCFC, but that won't be true for most people.
Hey Sam. I always appreciate your measured and well-explained comments on batteries.

Question... Do you think there's any significant difference for battery health on AC L2 power level? Many of us have home EVSEs that can easily be set anywhere from 16A to 48A. My Grizzl-E, for example, can be set at 16A, 24A, 32A, or 40A. Time is a non-issue for me. Any of the 4 settings would work fine since I don't put many daily miles on and my power company uses flat rate round the clock (no TOD pricing). Is there any advantage to lowering it from the 40A default, or is everything that low all the same for battery health?
 

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I plan to do the same thing I did with my Leaf and with my Bolt--100% charge. Of course, that does not charge the battery 100% because of the reserve, only charges to 100% of available battery. Neither my Leaf nor my Bolt ever had a problem with this or experienced any measurable battery capacity loss. Most charges were with an L2 charger.
I wholeheartedly agree. This idea that electric car batteries should not be fully charged/discharged has gotten a bit out of control. I have plugged my Honda Clarity PHEV into the wall every night for the past three years and have seen no measurable decrease in range.
 

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I wholeheartedly agree. This idea that electric car batteries should not be fully charged/discharged has gotten a bit out of control. I have plugged my Honda Clarity PHEV into the wall every night for the past three years and have seen no measurable decrease in range.
yeah I was just not going to worry about it, but I'm sure I'll be fine with 90% and it's what the manual says. Actually I'm going to have it at 90% during the week and 100% on the weekend, because who knows what I'll be doing on the weeekend

edit: app can't do that. ugh. ford please fix
 

phidauex

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Hey Sam. I always appreciate your measured and well-explained comments on batteries.

Question... Do you think there's any significant difference for battery health on AC L2 power level? Many of us have home EVSEs that can easily be set anywhere from 16A to 48A. My Grizzl-E, for example, can be set at 16A, 24A, 32A, or 40A. Time is a non-issue for me. Any of the 4 settings would work fine since I don't put many daily miles on and my power company uses flat rate round the clock (no TOD pricing). Is there any advantage to lowering it from the 40A default, or is everything that low all the same for battery health?
The tricky thing about battery degradation is that everything matters, just by different amounts. So the question is usually “does it matter enough for me to care”.

If you intend to keep this car more than 15 years, and you enjoy being fastidious with your cars (have you ever sent an oil sample from one of your ICE vehicles into a lab for analysis?), then there are all sorts of little things you could do to wring a few more cycles out of the battery.

However, for most people, just the basic rules of “leave it plugged in at home and only charge over 90% on days when you’ll need it” will do the trick.

That said, with L2 chargers there is going to be very little degradation difference between the available powers. Even a 48A charger is only 0.1C charge rate for the ER battery which is very gentle. I would have no concerns about leaving an L2 charger at full power.

Back when batteries were much smaller, that charger could be something like a 0.33C on a 30kWh battery, which might be higher than desired.

And again, technically you’d get a teeny bit less degradation if you backed the power off a little, but I think the potential gains are very small and not worth futzing with. How high of an SOC you charge to every night, and how many miles you drive per year will make a much bigger impact long term.
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