Daily charging/topping up the battery (even only to 80%) could be very bad

[yavore]

Daily charging / topping up the battery before certain depth of discharge should be killing your battery.

At least according to this sheet - source: The Secret Life Of An EV Battery, Cleantechnica.com

IMG

I added the last 2 columns just for clarity's sake.

So according to this sheet the best case scenario (battery wise) is 75% - 25%.

The case 75%-65% (small commute, topping up the battery every day) is actually horrible for the battery life.

So I'm puzzled. The general consensus is "a plugged in Tesla is a happy Tesla".

But what if the above conclusion is correct?

 

[N..8]

If this data was/is correct the 75%-65% isn't the worse for battery life. Your battery actually would be better but you wouldn't get your money out of the cost/used capacity. If a Cycle was daily then 12,000 days before 85% is better then just 10,000 days that's like 6 years.

 

[yavore]

One cycle is not equal to one day.
...
Let's assume 100 % of battery gives you 100 miles (for simplicity).

So 12.000 cycles x 0.1 (10%) x 100 miles = 120.000 miles

7.100 cycles x 0.5 x 100 miles = 355.00 miles

So I think discharging to 25 % is clearly better. With short commute you can charge once every few days.

 

[Rocky_H]

@yavore You are very very badly misinterpreting this data and stating incorrect conclusions.

Daily charging / topping up the battery before certain depth of discharge should be killing your battery.

No, it isn't.

At least according to this sheet - source: The Secret Life Of An EV Battery, Cleantechnica.com

That is not what that source says.

I added the last 2 columns just for clarity's sake.

You added false information in those columns, so it certainly did not help with clarity. Your third column says "Battery capacity used per 1 cycle". There should not be any different numbers in that column. A battery "cycle" is a specifically defined term, which always means 100% of its capacity. You are mistakenly thinking of one charging session as a "cycle", but that's not correct. Let's say you started at 75% and went down to 65% and then charged back up to 75%. You would have used and refilled 10% of the capacity of the battery, so that actually is only one tenth of a cycle. So it would take ten days of those recharging events to equal one cycle. That's how battery lifetime terminology is defined.

So according to this sheet the best case scenario (battery wise) is 75% - 25%.

The case 75%-65% (small commute, topping up the battery every day) is actually horrible for the battery life.

This is not correct. Column 2, which comes right from the article, tells you directly (without any extra incorrect columns added) which type of recharging is the best case and will get you get the most amount of cycles from the battery. It says that the 75% to 65% use case will get you about 12,000 total cycles, which is more total energy used over its lifetime, than the 7,000 or 4,000 or 2,000 of the other types of use, which have larger spans of usage between recharging.

But what if the above conclusion is correct?

The article's conclusion is correct. You are stating the opposite of what the article says.

 

[emir-t]

You might have misunderstood the article because of your misconception of what a cycle means. A cycle is 100% used independent from at which percentage it was charged. So;

Day 1: Used 10% = from 90% to 80%
Day 2: Used 20% from 80% to 60% then charged back to 90%
Day 3: Used 25% from 90% to 65% then charged back to 90%
Day 4: Used 45% from 90% to 45%

This whole 4 days total is one cycle.* So article really means the opposite.

* Actually not even since UI percentages aren't even real 100% An OG Model S 85 comes with 81kWh pack, of which 77kWh is usable and it is quickly deteriorated to 73kWh-ish usable in first 30k miles. With an average consumption of 340Wh/mi driving 100,000 miles is 34,000kWh used. 34,000/81 is 420 cycles.

 

[yavore]

@Rocky_H
I really hope that you are right and I'm wrong. Because I've been always charging daily (up to 80%) no matter what the depth of discharge is.

The article clearly states:
"It would appear that charging between 85% and 25% gives a good balance between battery life and workable capacity"

It all depends on whether the therm "battery charge cycle" is always 100%-0%-100% (as you stated) or one can have a shallow cycle (75%-65%-75%).
The latter would mean that my conclusions are actually correct.

Frankly I don't see how in the article you can mach your definition of "cycle" to the given examples.
So if you always discharge/charge 75%-65% (which is a shallow cycle of 10%) how can you have 12.000 full 100% cycles?
I don't get it.

 

[MarsBar]

I've owned Teslas for about 6 years and in that time I've supercharged a lot and also charged daily, often to 100%. If there has been any battery degradation, it's minor.

If you are trying to preserve your car so that in 10 years it has the same capabilities as it had when new, perhaps you should be zealous about how you charge. For most people, though, it shouldn't be a concern. I'd much rather enjoy the car and have it ready for longer trips without the need for stops.

 

[yavore]

You might have misunderstood the article because of your misconception of what a cycle means. A cycle is 100% used independent from at which percentage it was charged. So;

Day 1: Used 10% = from 90% to 80%
Day 2: Used 20% from 80% to 60% then charged back to 90%
Day 3: Used 25% from 90% to 65% then charged back to 90%
Day 4: Used 45% from 90% to 45%

This whole 4 days total is one cycle.* So article really means the opposite.

This is an excellent example. I guess I really misunderstood the therm "cycle".
So the 75-65% 12.000 cycles example from the article means that you can shallowly discharge/charge (10%) 120.000 times?
Is that correct?

 

[brkaus]

This is an excellent example. I guess I really misunderstood the therm "cycle".
So the 75-65% 12.000 cycles example from the article means that you can shallowly discharge/charge (10%) 120.000 times?
Is that correct?

That’s my take. I find the wording on the article confusing.

 

[ewoodrick]

This is an article by a gentleman that is using facts from another site without really understanding any of the issues. I honestly don't think that I found a single paragraph that I didn't disagree with.

• As other have suggested, a charge cycle is a 0-100% iteration. And that's the reason why Tesla and others don't recommend going to 0%.
• He's using lithium batteries in general, and as anyone who knows anything knows, there are HUGE difference in lithium batteries.
• He doesn't seem to understand a BMS, or even that there is one and its job to manage the battery charge
• He did write a big section on the derating of a battery pack, something that a single Model S had for a little bit.
• His limitations on charging is comical

I really like this one
"Fifty liters of fuel represents 600kWh of energy. A 600kWh battery would weigh 6 tons today. A 50kWh battery weighs half a ton — do you really want to be carrying around more than half a ton on all the short journeys you take every day, just to save a few charging stops on the occasional long run?"

So, in American terms, 13 gallons of gas, which at 25 mpg is 325 miles of range for an ICE doesn't require a 600 kWh battery, that's what the Model 3 gets with a 80 kWh battery.

 

[Rocky_H]

@Rocky_H
I really hope that you are right and I'm wrong.

This isn't your opinion or my opinion. The definition of a battery cycle is consistent in all battery research. It is always one full capacity of the battery pack. So the amounts of damage and the lifetime have to do with how that is used, if it's all at once, or spread out over some smaller sessions.
So you could do the 100% to 0% to 100% once, or you could go full to half to full twice, or you could go 75% to 25% and back twice, etc.

The article clearly states:
"It would appear that charging between 85% and 25% gives a good balance between battery life and workable capacity"

Yes, all of this has to be about a balance of a vehicle that is useful to the customer versus keeping a long battery lifetime. Best cases for batteries are staying near 50% just about all the time. But if you only allow 5 or 10% deviation off the midpoint, that is nearly useless driving range. So you do need to allow a wider expanse of state of charge for practical purposes while still preferably keeping it somewhat near midpoint.

Frankly I don't see how in the article you can mach your definition of "cycle" to the given examples.
So if you always discharge/charge 75%-65% (which is a shallow cycle of 10%) how can you have 12.000 full 100% cycles?
I don't get it.

Since "cycle" really does mean the full capacity of the battery, it is equivalent to energy. So the article is pointing out that using the battery in smaller increments like that will cause less damage to the battery, and you can run much more energy in and out of it (more cycles) over its lifetime before the overall capacity gets degraded too much from getting worn out. And since the energy used through the battery correlates to the miles of usage, it's a measure of how many miles of use before the battery is degraded.

 

[Rocky_H]

So the 75-65% 12.000 cycles example from the article means that you can shallowly discharge/charge (10%) 120.000 times?
Is that correct?

Yes, correct.

 

[TexasEV]

It always amuses me that people are willing to believe some random article they read on the internet more than Tesla’s battery engineers.

 

[yavore]

Yes, correct.

Thanks. Frankly I'm relieved. Topping up the battery is what I do and it gives me much more driving range comfort.
I've checked in the meantime the definition of charging cycle (should have done it before posting, I know) which is exactly what you explained.

 

[Rocky_H]

Thanks. Frankly I'm relieved. Topping up the battery is what I do and it gives me much more driving range comfort.
I've checked in the meantime the definition of charging cycle (should have done it before posting, I know) which is exactly what you explained.

I'm glad you got to that Wikipedia article after I changed it to match my opinion. Kidding!!!

 

[yavore]

I'm glad you got to that Wikipedia article after I changed it to match my opinion. Kidding!!!

I new there was something fishy there

 

[yavore]

.
I'm afraid after reading this (batteryunivercity.com) I have to reiterate the original claim that frequent shallow "charging/discharging sessions" (75%-65%) are much worse for the battery longevity than moderately deep charge/discharge (75%-25%). Direct conclusion - no more daily plug in (before reaching 30-25% SoC).

I realize this is not a big deal as there are so many other factors to consider regarding the battery degradation (time and temperature for example). However I' d appreciate any help in clarifying this "charge cycle meaning" controversy:

This actually comes to confirm (if I'm not mistaken again) the sheet I posted originally. 90.000 EU (energy units) vs 150.000 EU.
It seems that 75%-25% wins.

Furthermore even batteryunivercity (which seems to me as the ultimate information source in this matter) states: "There is no standard definition as to what constitutes a discharge cycle."

Please let me know what you think of it.

 

[TexasEV]

Please let me know what you think

I think y’all are too obsessed over the battery. How many decades do you plan to drive this car? Do you realize that tens of thousands of Model S owners have not lost significant range no matter how the car was charged (many of us charging to 90% every night, and 100% for trips)?

Chill out and enjoy driving the car. Or worry about possibility having a percent or two less range in a 310 mile car after many years. Your choice.

 

[steven55]

Yavore, I think your opinion is correct. The charging cycle is different from the battery cycle.

"DST Cycles" and "cycles of Column 2" are charging cycle.

 

[davecolene0606]

Trust in JB...

Put it in daily mode plug in every opportunity let the BMS take care of it.

Fire Away!