What type of range degradation to be expected?

[Peter_M]

No, that is not the basis for normal degradation. Time at near 100% at high temperatures will accelerate the degradation, but since Tesla water cools their packs you have to do it a LOT in order to impact the capacity.

My point that time spent near 0% or 100% is the biggest factor in Li-ion cell degradation came from this presentation (by the guy that Tesla later signed on to do research for them). The video is long but quite interesting. He's talking about cells, not battery packs, so you're right that thermal management in the pack will mitigate these effects, but he makes the point several times that the number of charge cycles isn't a very good predictor of battery lifetime.

 

[agloutney]

I think the best comparison is to compare your ideal range at 100% to what it was when new. Apparently they don't tweak the software as much for that setting or something to that effect.
I'm getting 488km at 37000km on an E revision 85 pack. That's a loss of 4km over 22 months. 90% rated gives me 379 down from 386 new. At this rate I can see myself keeping this car at least 20 years if everything else holds together.

 

[Doug_G]

My point that time spent near 0% or 100% is the biggest factor in Li-ion cell degradation came from this presentation (by the guy that Tesla later signed on to do research for them). The video is long but quite interesting. He's talking about cells, not battery packs, so you're right that thermal management in the pack will mitigate these effects, but he makes the point several times that the number of charge cycles isn't a very good predictor of battery lifetime.

Well he's simply wrong. The data that Tom Saxton has compiled is extremely convincing. He's studied it from all angles - in the real world, the car range is a function of pack cycles (aka mileage) and nothing else. Age of packs controlling for range does not correlate at all, which it would otherwise.

 

[Peter_M]

Well he's simply wrong. The data that Tom Saxton has compiled is extremely convincing. He's studied it from all angles - in the real world, the car range is a function of pack cycles (aka mileage) and nothing else. Age of packs controlling for range does not correlate at all, which it would otherwise.

Well, I'm not an expert, but watch Dr. Dahn's video and see if you still want to call him wrong. Tesla seems to think he's a world leader on battery lifetime.

I don't understand your point "Age of packs controlling for range does not correlate" - I'm not saying pack age determines degradation. It's the total amount of time that the cells are left sitting at near 0% or 100%, because there are parasitic chemical reactions that occur in this state (when the lithium ions are concentrated around one of the electrodes) and those reactions "clog up" the electrode, limiting the cell's charge capacity. And high temperature accelerates those parasitic reactions. (Which is presumably why Tesla tells us not to leave the battery at 100% too much.)

In other words, cycling 100 times from 40% to 60% over 100 days would degrade the battery much less than charging once to 100% and leaving it there for 100 days. At least that's the impression I got from the video, but again I'm not an expert...

 

[Doug_G]

Okay, let's break this down.

Yes - if you leave a cell at 100%, especially at high temperatures, it will degrade relatively quickly. Correct. The thing is, that doesn't happen except in rare cases of abuse/stupidity. Tesla does everything it can to prevent you from doing this. It actively cools the battery pack to reduce degradation over time. It defaults to 90% charging. If you leave the car set to charge at 100%, it posts warning messages. If you ignore them, then yes you will degrade your battery faster. But Tesla has taken measures and the real-world data indicates that they are effective.

Also I should point out that some people get this paranoia that you should never 100% charge the car. This is incorrect - if you charge to 100% and then use it shortly thereafter, the total time spent at 100% is minimal and the effect is negligible. As long as you do what the car tells you to do, it's not an issue at all.

What real-world data clearly reveals is: for the vast majority of Tesla vehicles, which are operated correctly, battery degradation correlates very well to total mileage, and does not correlate with other factors.

 

[hingisfan]

Okay, let's break this down.

Yes - if you leave a cell at 100%, especially at high temperatures, it will degrade relatively quickly. Correct. The thing is, that doesn't happen except in rare cases of abuse/stupidity. Tesla does everything it can to prevent you from doing this. It actively cools the battery pack to reduce degradation over time. It defaults to 90% charging. If you leave the car set to charge at 100%, it posts warning messages. If you ignore them, then yes you will degrade your battery faster. But Tesla has taken measures and the real-world data indicates that they are effective.

Also I should point out that some people get this paranoia that you should never 100% charge the car. This is incorrect - if you charge to 100% and then use it shortly thereafter, the total time spent at 100% is minimal and the effect is negligible. As long as you do what the car tells you to do, it's not an issue at all.

What real-world data clearly reveals is: for the vast majority of Tesla vehicles, which are operated correctly, battery degradation correlates very well to total mileage, and does not correlate with other factors.

I would generally agree. Babying the battery at 40 to 60% instead of just topping up to 90% every night, over the course of a several years and a couple hundred thousand kms, we might be talking about 1 or 2% difference. Just my opinion/guess.

 

[beeeerock]

What primarily determines the capacity degradation is number of pack cycles, i.e. how many times the pack has been discharged and recharged. (With Lithium ion chemistry ten cycles of 1/10th are pretty much the same as one full cycle.) A good proxy for pack cycles is total car mileage, assuming that average usage/km is fairly constant across the fleet. (The correlation is not perfect, i.e. total power used is more accurate, but the difference is tiny.)

So with the assumption that ten 1/10th cycles are equal to one full cycle, is there a strategy to extend battery life? I typically charge daily to 80% or 90%, depending on what I expect to be doing the next day. Some days I've lost more power to vampire losses than to actual driving (the losses are actually quite high...), but I plug in when I get home anyway - even if I've only gone 10 or 15 km. The understanding that a Happy Tesla is a Plugged in Tesla has governed my habits.

If charge increments add equally and proportional to their actual size, then I don't think there is a strategy... or am I missing something?

 

[AZ Desert Driver]

I think the best comparison is to compare your ideal range at 100% to what it was when new. Apparently they don't tweak the software as much for that setting or something to that effect.
I'm getting 488km at 37000km on an E revision 85 pack. That's a loss of 4km over 22 months. 90% rated gives me 379 down from 386 new. At this rate I can see myself keeping this car at least 20 years if everything else holds together.

I pick up my 60D tomorrow- how do I do a time-zero pack reading?

 

[Peter_M]

Okay, let's break this down.

Yes - if you leave a cell at 100%, especially at high temperatures, it will degrade relatively quickly. Correct. The thing is, that doesn't happen except in rare cases of abuse/stupidity. Tesla does everything it can to prevent you from doing this. It actively cools the battery pack to reduce degradation over time. It defaults to 90% charging. If you leave the car set to charge at 100%, it posts warning messages. If you ignore them, then yes you will degrade your battery faster. But Tesla has taken measures and the real-world data indicates that they are effective.

Also I should point out that some people get this paranoia that you should never 100% charge the car. This is incorrect - if you charge to 100% and then use it shortly thereafter, the total time spent at 100% is minimal and the effect is negligible. As long as you do what the car tells you to do, it's not an issue at all.

What real-world data clearly reveals is: for the vast majority of Tesla vehicles, which are operated correctly, battery degradation correlates very well to total mileage, and does not correlate with other factors.

OK, we're in agreement now. I was talking about what causes a Li-ion cell's lifetime to degrade, not how battery packs in cars degrade in real life when people follow good practices. Yes, Tesla does a lot to make sure we don't do things that cause the cells to degrade, but if you ignore that and leave your battery at 100% for many hours every day, it will degrade faster than if you follow Tesla's advice. I was just pointing out some scientific info I had seen about why that's the case.

Having watched that video about Dr. Dahn's research and his very impressive lab, I was happy to hear that Tesla has signed him up to do research for them. Maybe he and his team will come up with some incremental improvements in electrolyte chemistry electrode design, charge management, etc.

 

[Doug_G]

So with the assumption that ten 1/10th cycles are equal to one full cycle, is there a strategy to extend battery life? I typically charge daily to 80% or 90%, depending on what I expect to be doing the next day. Some days I've lost more power to vampire losses than to actual driving (the losses are actually quite high...), but I plug in when I get home anyway - even if I've only gone 10 or 15 km. The understanding that a Happy Tesla is a Plugged in Tesla has governed my habits.

If charge increments add equally and proportional to their actual size, then I don't think there is a strategy... or am I missing something?

The ideal would be to keep the pack in the middle of the charge range, but that is only incrementally better than 80% or 90%. And that is only practical if your car is in long-term storage!

It's actually not good for the pack to be drawing power at a low state of charge. In order to make up for the lower voltage, the car has to draw more current. So during operation a higher state of charge is actually better.

The best compromise, IMHO:

• Always keep the car plugged in when you can. (Nightly... you don't have to do that while at work!)
  
• Charge your car daily to 80% in summer. You don't need the extra power for daily drives.
• Charge your car daily to 90% in winter. It's good to have a little extra power with the greater winter power draw, and because it's colder the degradation at high SOC is much much smaller.
  
• If you store the car for weeks or months, set it to 50%.
  
• If you go on a long trip, don't hesitate to charge to 100%. It's far better to fully charge for a brief interval than to risk running out of charge or going to very low SOC, which isn't good for the battery either. Don't leave it at 100% for weeks... just charge it, drive it, and go back to 80/90.
  
• In winter, preheat the car using the remote app while plugged in. Remote app prewarming will heat the cabin and the battery pack. That uses power from the socket instead of the pack. Less pack wear.

 

[Doug_G]

Interesting... 200k, 100% daily, and only 6% degradation:

Tales from a Tesla Model S at 200k miles

 

[ecarfan]

Interesting... 200k, 100% daily, and only 6% degradation:

Tales from a Tesla Model S at 200k miles

After hundreds of 100% charges that is an astonishingly minor amount of battery degradation.

 

[Matteo]

Hi,

In addition to the data provided by others, here is a chart from the MaxRange Battery Survey. You can add your data if you want and then select your username on charts page and it will show your entries in a different color like this. Let me know if you have any questions. I provide free technical support for this project.

 

[AZ Desert Driver]

How do I get my "mile zero" (and all other) Range readings? What button do I push to get it? Do I set my 60D to 100% charge, knowing that it is only 80%?

 

[Doug_G]

Most accurate way is to run it down low (but not too low!) and then charge to 100%. Read it as soon as it stops.

 

[Matteo]

How do I get my "mile zero" (and all other) Range readings? What button do I push to get it? Do I set my 60D to 100% charge, knowing that it is only 80%?

@AZ Desert Driver,
The Model S doesn't report what the rated range was when the car was new. These numbers are published on Tesla website, as well as the EPA website HERE. On that page, you can see that the S60D has 218 miles EPA rated range. That's the number the sheet uses in calculations. What you need to enter is, your rated range when you last charged to 100%. There is an optional question that asks what your rated range was when the car was new. If you don't know this, you can skip it. This is not used in calculations. I use this number to fine-tune the calculations. For example, most S85 owners reported that the car displayed 267 mi rated range with range mode on when it was new. Therefore, instead of the official 265 mi on EPA, the sheet uses 267 in all S85 calculations. So far there hasn't been any S60D entry. Therefore the 218 mi official number will do for now until many people report that new S60D's were displaying actually something different.

 

[beeeerock]

The best compromise, IMHO:

• Always keep the car plugged in when you can. (Nightly... you don't have to do that while at work!)
  
• Charge your car daily to 80% in summer. You don't need the extra power for daily drives.
• Charge your car daily to 90% in winter. It's good to have a little extra power with the greater winter power draw, and because it's colder the degradation at high SOC is much much smaller.
  
• If you store the car for weeks or months, set it to 50%.
  
• If you go on a long trip, don't hesitate to charge to 100%. It's far better to fully charge for a brief interval than to risk running out of charge or going to very low SOC, which isn't good for the battery either. Don't leave it at 100% for weeks... just charge it, drive it, and go back to 80/90.
  
• In winter, preheat the car using the remote app while plugged in. Remote app prewarming will heat the cabin and the battery pack. That uses power from the socket instead of the pack. Less pack wear.

Thanks Doug. This pretty much reflects my strategy so good to have confirmation I'm not completely out to lunch!

Something I find interesting in the way the charge level is calculated is how it will wander a little over time... not just down, but also up. I always note how many km are shown when my standard charge (80% these days) completes. Typically 343 km, but sometimes it will show 342 for a few days... then after a longer run that draws the battery down lower than normal, I'll perhaps see 344 km for a while. Presumably that's the calibration happening when more of the battery is 'seen'. It follows that the whole concept of degradation is pretty empirical given the way the software decides how much battery capacity we actually have. I've been suspicious that the 85kWh pack actually has some reserve locked away, as the full kWh from charged to discharged seems to have more 'left over' when compared to the pack rating... than other battery pack sizes seem to show.

 

[Doug_G]

It's something of a myth to say that a battery has a particular "capacity". It's up to the designer of the machine using the battery to decide what voltage is "too high" and "too low". Once you decide what voltage range you are going to subject it to, the difference between those two numbers determine how much energy you can get out of it. The manufacturer will recommend a particular range, and thus advertise a capacity, but to preserve battery lifetime it's probably prudent to be more conservative.

If you are more conservative with the voltage range, you will get less driving range. I believe Tesla is appropriately conservative. They also actively control the temperature range the batteries are subjected to. This makes a big difference.

Laptop computers are often advertised with "5 hour battery life" or such. Unfortunately Li-Ion batteries don't like being charged to 100% and subjected to high temperatures - which is exactly what most laptops do to them. They get hot, and most of them always top the battery right up. So the only time you get your 5 hours of battery life is during its first month of operation! Two years later the thing will barely last 20 minutes. In order to be able advertise a longer "battery life", they're destroying the lifetime of the batteries. This nonsense gives Li-Ion batteries an undeserved bad rep.

 

[Aussie Bob]

The ideal would be to keep the pack in the middle of the charge range, but that is only incrementally better than 80% or 90%. And that is only practical if your car is in long-term storage!

It's actually not good for the pack to be drawing power at a low state of charge. In order to make up for the lower voltage, the car has to draw more current. So during operation a higher state of charge is actually better.

The best compromise, IMHO:

• Always keep the car plugged in when you can. (Nightly... you don't have to do that while at work!)
  
• Charge your car daily to 80% in summer. You don't need the extra power for daily drives.
• Charge your car daily to 90% in winter. It's good to have a little extra power with the greater winter power draw, and because it's colder the degradation at high SOC is much much smaller.
  
• If you store the car for weeks or months, set it to 50%.
  
• If you go on a long trip, don't hesitate to charge to 100%. It's far better to fully charge for a brief interval than to risk running out of charge or going to very low SOC, which isn't good for the battery either. Don't leave it at 100% for weeks... just charge it, drive it, and go back to 80/90.
  
• In winter, preheat the car using the remote app while plugged in. Remote app prewarming will heat the cabin and the battery pack. That uses power from the socket instead of the pack. Less pack wear.

Thanks Doug. This is basically what I have been doing since I took possession of the car, especially the 50% charge when we travel for several months.

 

[DMC-Orangeville]

85D bought March 2015 - 50,000 KM. 90% new was 392 KM. Went down to 382 KM- then balanced it this summer (2 X 100% charges, and 2 recharges near 0%*). Brought the range back up to 386 KM after balancing the cells.

*Kingston SC was running REALLY slowly, and I had to be at a wedding. Rolled into Kanata with 3 KM of range. Fortunately the venue let me plug in at 120V for 4 hours. Enough to get me to the hotel and a nearby PlugShare. @Doug_G 's charger was too far away to visit!