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

[MtHamilton]

I may be off base here, but arguing theoretical battery life may not be important. I have a 85 battery with 60k miles. A year or two ago, the battery had a problem, had to be pulled, and spent close to a month for a rebuild (apparently contracted out for remote repair). Now, the car is in for a second time for another 3-4 week rebuild (Service says it will get a new battery, but I doubt Tesla will give one to me). My fear is that since the battery is lasting only a few years before failure requiring battery rebuild, I need to dump it before I reach the warranty's conclusion at 8 years. Not having the car for a couple of months saves on charge cycles, but I'd rather have my car working reliably. Range reduction has not been noticeable, so I am not sure charging every time I am at home makes much difference.

By the way, the first time, a warning message turned on and I was able to go to the local service center. This time, there was no advance notice. The car just decided to indicate service required as it shut down after being parked for several hours in a public garage (dead - would not go into tow mode; yes, Tesla changed the 12 volt 8 months ago).

With this track record, the car will not make it to 90k, though there might be plenty of life theoretically left on the battery.

 

[Long Ranger]

If the graph is correct (and if applicable to all type of lithium batteries) - the best scenario (among those on the graph) is clearly 75%-25%.

At 90% capacity retention (i.e. the same SoH) , the 75-65 case has given only 90.000 EU whereas 75-25% has provided 150.000 EU.

No, 75-25% is not clearly better if you look closely at the graph itself. You keep focusing on the 90,000 EU number in the note from battery university. That number is not supported by the graph itself.

To compare the two charging scenarios in terms of equivalent EU, scale the x-axis by a factor of five for one set of data points (each charge of 75-25 has 5x the energy of a 75-65 charge). Plot each 75-25% data point 5x to the right (250 moves to 1250, 500 to 2500, 750 to 3750, 1000 to 5000, etc). You can see that the curves are almost identical. In fact, the orange 75-65% curve is often slightly above the scaled blue 75-25% curve, including at the last valid comparison point, 1500 vs. 7500 test cycles.

Battery university was making some guesses about where the 75-65% curve might cross the 90% threshold, which isn't a valid data point on the graph. I don't think those guesses are relevant either: the graph goes up to 8400 test cycles, which would be 23 years of charging 75-65% once per day.

 

[SageBrush]

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

I read posts that think you understand the article wrong but I am not one of them.
OTOH, a person charging daily between 65% and 75% would drop capacity down to 85% in 12000 days, equal to ~ 32 years.

The more important lesson is probably to set your daily battery use to cycle around 50% so that a 10% daily use would start the day at 55% SoC and end at 45% if you are keen to charge daily. I personally find it convenient to plug-in when my remaining charge is below 110 miles and charge up to 250 miles (about 35% - 80%) for my routine driving of 90 miles per jaunt.

 

[Futuresystem]

It’s that absolute top and bottom area of charge that is hard on the battery. The middle area is just bordering on acedemic whether you do a small daily charge in the mid section (say 45%-55%) or less often with a slightly wider spread (say 25-75%).
You can actually achieve the same results with your smartphone battery...
IF you don’t fully charge it and don’t fully discharge it you’ll extend the phone’s battery life dramatically. (The phones of course don’t give you the setting option for a less than full charge because they don’t WANT the battery to last too long- they want you to go and buy a new phone.)
As an example I have an iPhone 7 which almost never gets fully charged or fully discharged, but is often topped up a little during the day, and mostly to no more than about 80- 85%. The battery state of health still says (and acts like) 100%. Compare that with another family member -his iPhone 7 is the exact same age, is nearly always fully charged and very often fully discharged- his battery is pretty sick and will need replacing very soon.

 

[Azndaemon]

So... What's the conclusion? I feel like I read 3 pages and only one thing people agree on is to stay as close to 50% as possible to maximize the battery's life expectancy.

There's no concensus on 75%-25% once a week vs 55%-45% 5 times a week ?

 

[Candleflame]

while you guys are still trying to figure out that a cycle is 100% i'm here to point out that 5000 cycles is already over 1.5 million miles. I'm sure 99.9999% of owners will never hit this anyway. In europe cars count as ancient when they have 200k miles.

when you eventually get there in 20 years you obviously get yourself a cheap aftermarket 200kwh battery for your model 3.

 

[Long Ranger]

So... What's the conclusion? I feel like I read 3 pages and only one thing people agree on is to stay as close to 50% as possible to maximize the battery's life expectancy.

There's no concensus on 75%-25% once a week vs 55%-45% 5 times a week ?

As far as lithium battery charge cycles go, there's tons of literature out there that says it doesn't really matter if you do 75-25% vs. 55-45% or 75-65%. I think we've pretty well debunked the claims here that 75-25% is superior.

The reason to plug in more often is basically because that's what Tesla recommends. There's more to battery life than just charge cycles. Temperature is also a big factor. With the car plugged in, the car is more likely to run battery conditioning to keep the battery at a good temperature. When unplugged, the car is less likely to run battery conditioning, because it doesn't know when it might get its next charge.

 

[yavore]

If I charge from 65% to 75% every day, then I hit 85% battery capacity at 12,000 days. That's 32 years! I should be so lucky...

I wish my commute was as short as yours

 

[Ficheh]

Since the battery warranty is 8 years, this really is not an important question now. What is important is if the battery does degrade, you want it to degrade to under 70% before the 8 year warranty expires. That way you'll get a brand new battery. If you try to keep your battery from degrading quickly, and it happens to only degrade to 85% after 8 years. You will have 85% vs 100% because you will have gotten a new battery at that point. Now once that 8 years have passed, then read what should be an extensive list of charging data, and choose wisely at that point.

 

[yavore]

3. The 90,000 vs. 150,000 EU calculation is simply wrong. The 90,000 assumes that the 75-65% line crosses 90% at 9000 test cycles. The data doesn't go out that far. Maybe it crosses 90% at 15000 test cycles, which would give 150,000 EU. We don't know.

The 90% SoH at 9.000 cycles estimation in the article is much more logical than yours (90% at 15.000 cycles).
Because of this:

Source

As the battery degradation develops - the difference in the delivered EU (energy units) gets even bigger:
At 90% SoH (10% degradation) it's 150.000 EU vs 90.000 EU.
At 85% SoH (15% degradation) it's 355.000 EU vs 120.000 EU.
75%-25% is clearly better in terms of energy units delivered per % of degradation.

Take the 95% retention point. 75-65% crosses at about 3000 test cycles, 75-25% crosses at about 600 test cycles. Both are then equal at about 300 EU.

Why not take then the 99.99 % retention point? For sure all the cases would be equal. At 1 EU delivered.
As already said - the gap widens with the increase of degradation.

Could you please show me any graph, article, any info supporting your claim that 75-65 is superior to 75-25 in terms of energy units delivered per % of degradation. I'll accept also any info supporting 55-45 is better in this regard.

 

[MarcoRP]

15 disagrees already. I feel like the Française don’t understand the Englishe as well. Ah tabarnac (comme on dit au Quebec!)

 

[tomas]

I completely agree with that. My obsessions is not that much about the battery of my car going bad - it is more about finding the general principle, applicable not only to the EVs but to your phone, laptop, tennis ball machine etc....

Then why the “very bad” alarmist spectacular thread title?

Suggest not to attempt a theotlry of all batteries. Your laptop is not your Tesla is not your tennis ball machine.

 

[yavore]

Then why the “very bad” alarmist spectacular thread title?

I'm open minded and I change my mind when I see convincing arguments.
If I could I would change the title to "may not be the best"

However 120.000 EU vs 355.000 EU seems pretty "bad" to me.

 

[yavore]

15 disagrees already. I feel like the Française don’t understand the Englishe as well

Very good point.
Nr of disagrees (15 or more) = not a valid argument.
Or even better: lack of English fluency = not a valid argument

 

[DarrenK]

If I charge from 65% to 75% every day, then I hit 85% battery capacity at 12,000 days. That's 32 years! I should be so lucky...

Is there anywhere you aren't?

 

[Long Ranger]

Could you please show me any graph, article, any info supporting your claim that 75-65 is superior to 75-25 in terms of energy units delivered per % of degradation. I'll accept also any info supporting 55-45 is better in this regard.

OK. I'll use your own source to show that. First, you are quoting a cleantechnica article which sites batteryuniversity.com as its source. I don't believe batteryuniversity.com has the table that you keep quoting (at least not that I can find). batteryuniversity.com does have the graph that you showed, and batteruniversity.com sites this paper as the source of that graph:
https://www.researchgate.net/profil...Life-Assessment.pdf?origin=publication_detail
Here is that graph, but I've added an orange line to show the 75-25% case with the x-axis scaled exactly 5x (I counted pixels to do this exactly). I scaled it 5x because the 75-25% case provides 5x the energy per charge compared to the 75-65% case. This way you can compare the orange and yellow lines to compare EU delivered per % degradation. You can see that the lines track really well with one another and there isn't any appreciable difference. Wherever the yellow line is above the orange line, the 75-65% case actually has superior EU delivered per % degradation.

Why not take then the 99.99 % retention point? For sure all the cases would be equal. At 1 EU delivered.
As already said - the gap widens with the increase of degradation.

I'm saying look at every point along the entire graph. You are the one who is only looking at a single data point (and that data point is actually off the end of the graph). If you compare the entire graph, there is no appreciable difference between degradation for the 75-25% case vs. the 75-65% case up through 8000 charge cycles (which is 22 years at one charge per day). You are taking a data point at 9000 or 12000 cycles and claiming that the yellow line dives below the orange line at that point (with very little evidence to prove that this data point is even real) and saying that the yellow line is much worse because of that single questionable point. So because the 75-65% line might drop ~2% below the orange line at 9000 charge cycles (24.6 years of daily cycles) we're suppose to believe that the orange line is far superior?

Also, as I previously noted, this example was taken from batteries using the LMO chemistry which is not good at retaining capacity over large numbers of charge cycles (used in the original Nissan Leaf). Look at this graph from the same paper:

Unfortunately, it doesn't show the NCA chemistry used by Tesla. However, you can see that the other two chemistries are definitely superior to LMO when it comes to a 10% Depth of Discharge (DOD). With LMO, 10% DOD provides close to 5x the cycles of a 50% DOD, which is why the 75-65% (10% DOD) and 75-25% (50% DOD) cases are so close with an LMO battery. However, if you look at the NMC chemistry in the above graph, you can see that a 10% DOD provides over 10x more cycles than a 50% DOD. So for NMC chemistry, 75-65% would be far superior to 75-25%.

All of this however, is really in the noise when it comes to battery degradation. If you read through this paper or other battery modeling papers, you'll see that degradation is a function of many other parameters such as age, temperature, and average state of charge. You'll generally find that those factors tend to dominate.

 

[yavore]

@Long Ranger

Thank you for taking the time to bring some arguments.
Let's just agree to disagree.
Except for this:
"All of this however, is really in the noise when it comes to battery degradation. If you read through this paper or other battery modeling papers, you'll see that degradation is a function of many other parameters such as age, temperature, and average state of charge. You'll generally find that those factors tend to dominate."

For me however 75-25% remains clearly superior in terms of energy units delivered (not taking into account the other components of the battery degradation).

I feel like 55-45 (but not 75-65!) may be better but it's just a feel - I couldn't find any info in conclusive support to this scenario.

 

[VT_EE]

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?

Take a MacBook Pro for example. You can read the cycle count from the System report. My 6 year computer is reading 218 cycles on the battery. I guarantee you it has been plugged in and charged far more than that. In fact, I plug it in every day and it tops off the battery. A cycle = many partial charges.

 

[KD4MNI]

On the topic of getting the most life out of our Tesla battery packs ...
I'm fairly new to the site and this discussion, but as an experienced EE. I would expect the RATE of recharging to be a major - possibly the dominant - factor in battery pack life expectancy. Has this recently been discussed? I can see how it could be a touchy topic ...
Charging is never 100% efficient, and the excess heat that's generated affects the recharging chemistry in complex ways. In general, slower recharging is better (although my understanding is that using the Tesla Mobile Connector to slow-charge from standard 120Vac is relatively inefficient compared to 240Vac charging).
Does excessive use of Tesla Supercharger Level 3 dc fast charging degrade battery pack longevity? Likewise for regular use of the most powerful Level 2 ac charging stations (50A / 12kW and higher)? In other words, does frequent "fast charging" significantly degrade battery pack life expectancy?

 

[xilex]

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.

Ya, my MPG on my 7 y/o gas car has slowly gotten worse. Dealer going to laugh me out of the shop if I tell them about it.

I've seen this posted around: MaxRange Tesla Battery Survey (see Stats tab). Small sample size for how much % charged to, supercharging frequency, etc. Maybe more reassuring for people who want numbers. I supercharge to 90%, get about 87% after driving home, and wait until I get worried at 50% to charge up again (b/c home charging dead).