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Is leaving Tesla plugged in while not charging really beneficial?

Rocky_H

Well-Known Member
Feb 19, 2015
8,125
10,350
Boise, ID
I find it odd Tesla wouldn't give a warning if it harms long term health of the batteries to exceed 50%.
Why would that be odd? That would murder their ability to sell cars to the general public. They need to sell cars that people can use. They can't announce that. They have to give some balanced advice and recommendations of a product that people can actually practically USE, while also trying to discourage the worst cases that do cause the most damage. So they have that general recommendation for daily use of not going over 90% to try to prevent the most extreme worst charging behavior. But people do need to feel free to have enough range to drive with.
 
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Why would that be odd? That would murder their ability to sell cars to the general public. They need to sell cars that people can use. They can't announce that. They have to give some balanced advice and recommendations of a product that people can actually practically USE, while also trying to discourage the worst cases that do cause the most damage. So they have that general recommendation for daily use of not going over 90% to try to prevent the most extreme worst charging behavior. But people do need to feel free to have enough range to drive with.
Read my post Rocky. It says 50% not 90%.
Announcement?? No I did not recommend an announcement.
Somebody on this thread says it harms the battery life to charge over 50% . I doubt that hence my comment. Does it??
 
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The original question in the thread, is it helpful to plug in at all times ? Why do you always plug in when you park in the garage? Does this extend the battery life? There seem to be some differing opinions on this.
Yes, I always plug in. Reducing average depth of discharge reduces degradation from cycling the battery.

Why would that be odd? That would murder their ability to sell cars to the general public. They need to sell cars that people can use. They can't announce that. They have to give some balanced advice and recommendations of a product that people can actually practically USE, while also trying to discourage the worst cases that do cause the most damage. So they have that general recommendation for daily use of not going over 90% to try to prevent the most extreme worst charging behavior. But people do need to feel free to have enough range to drive with.
Their concerns are not necessarily the same as the concerns of vehicle owners. They don't want to be doing warranty replacements. But they're not necessarily concerned with minimizing everyone's battery degradation at all costs.

I have plenty of range to drive with, so long as I plan ahead for any trip requiring more than 50% SoC (and by "plan ahead" I mean I'd need about 4-5 hours notice to get from around 35% to 100%). Since it's rare that I'd ever go more than 130-170 miles in one day without knowing about it in advance, this works well enough.
Read my post Rocky. It says 50% not 90%.
Announcement?? No I did not recommend an .
I'm a member of the general public and I'd like to know if it harms the battery life to charge over 50% as one poster here says. Does it??
Higher SoC means higher calendar degradation. There isn't a cutoff point below which this trend stops; it's a continuous function. So yes, it does. But the advantage of keeping it at 90% instead of 100% is large. The advantage of keeping it at 80% instead of 90% is still large but smaller. 70% vs. 80% is smaller still. But there is still an advantage of going all the way down to 50%.
 
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Yes, I always plug in. Reducing average depth of discharge reduces degradation from cycling the battery.


Their concerns are not necessarily the same as the concerns of vehicle owners. They don't want to be doing warranty replacements. But they're not necessarily concerned with minimizing everyone's battery degradation at all costs.

I have plenty of range to drive with, so long as I plan ahead for any trip requiring more than 50% SoC (and by "plan ahead" I mean I'd need about 4-5 hours notice to get from around 35% to 100%). Since it's rare that I'd ever go more than 130-170 miles in one day without knowing about it in advance, this works well enough.

Higher SoC means higher calendar degradation. There isn't a cutoff point below which this trend stops; it's a continuous function. So yes, it does. But the advantage of keeping it at 90% instead of 100% is large. The advantage of keeping it at 80% instead of 90% is still large but smaller. 70% vs. 80% is smaller still. But there is still an advantage of going all the way down to 50%.
Good. I keep it at 50% or less unless going on a trip. I actually wish the GUI would allow you to set a limit less than 50%.
You say always plug in. Even when leaving for just a few hours or overnight? Thanks for the input.
 

Rocky_H

Well-Known Member
Feb 19, 2015
8,125
10,350
Boise, ID
Read my post Rocky. It says 50% not 90%.
Yes, I read it. I knew you said 50%, and that is what I was talking about.
Announcement?? No I did not recommend an announcement.
Really? It sounded like you did:
I find it odd Tesla wouldn't give a warning
To "give a warning" seems like the same thing as saying (or announcing) something. You said it seems odd they would not tell this to people. And I was pointing out that they have good reasons for not wanting to say this. They don't want to scare people away or give the impression that the cars aren't very usable by telling them that it is bad for the car's battery to charge over 50%. They have to make them sound not scary enough that people will want to buy them.
Somebody on this thread says it harms the battery life to charge over 50% . I doubt that hence my comment. Does it??
Yes--some. There is data showing that the best, most ideal, most avoiding-damage place for the batteries to sit is around 40% or so. But that's not a very practical way to use a car to keep it less than half all the time, so Tesla can't really recommend that to everyone.

But as @STS-134 was describing, it's getting into pretty fine hair splitting looking at the distinctions between 40% usage or 50 or 60%. Sure, those higher ones are just barely worse, but noticeable in 20 or 30 years? Eh, maybe. But they want to try to warn people away from the worst case that shouldn't have too much of an impact on how people can use the cars.
 
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You're harming the long term health of your batteries if you're charging above 50% when you don't need to. My vehicle is pretty much always below 50% (the charge limit is set to 50%) except when I am doing longer trips, and when I do that, it charges up just before I leave so the amount of time spent over 50% is minimized. I always plug in when I park in the garage.
Wait what? Charging above 50% harms the battery?
 
I currently have the charge limit set to 90%, which is the default Tesla value. Available research indicates that 80% would be a better limit, but the wife is opposed to further restrictions on range. She starts to develop range anxiety when getting close to 100 miles (30% of 330 miles), which is a good thing. I did reduce the charging current on the mobile charger from 32A (default) to 25A, since that provides enough time (9PM to 6AM) to charge from 100 mile to 297 miles (90%). That also means that the charge is complete just prior to when she uses the car in the morning. Automatic pre-conditioning, if you will.

The only time the charger is plugged in is when we want to charge at the scheduled start time.
 
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I currently have the charge limit set to 90%, which is the default Tesla value. Available research indicates that 80% would be a better limit, but the wife is opposed to further restrictions on range. She starts to develop range anxiety when getting close to 100 miles (30% of 330 miles), which is a good thing.

Does she really use 60% a day? If not, you could charge daily to a lower limit and still stay above 30%.

I charge every night. I never charge to 90% unless I need it the next day, which would usually mean a road trip.

Normally I charge to 60%, use 20%, and arrive back at home with 40%. This is my current habit after 17,000 miles.

I did reduce the charging current on the mobile charger from 32A (default) to 25A, since that provides enough time (9PM to 6AM) to charge from 100 mile to 297 miles (90%).

Honestly, as far as battery degradation goes, it makes no difference whether you charge at 32A or 25A. Same goes for charging with 48A from a wall connector.
 
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Does she really use 60% a day? If not, you could charge daily to a lower limit and still stay above 30%.

I charge every night. I never charge to 90% unless I need it the next day, which would usually mean a road trip.

Normally I charge to 60%, use 20%, and arrive back at home with 40%. This is my current habit after 17,000 miles.



Honestly, as far as battery degradation goes, it makes no difference whether you charge at 32A or 25A. Same goes for charging with 48A from a wall connector.
IMHO, charging every day is a waste of time. As for charging current, lower values result in less heat buildup in the battery and having the charge cycle end just before the wife uses the car in the morning provides automatic preconditioning.
 
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I wonder if an excessive number of charges to 100% or discharges below 10% can eventually cause a cell to fail? Or are some cells doomed to fail no matter what?
The answer is “yes.” Some cells are doomed to fail early in life, regardless of operating conditions. Others may maintain optimum performance regardless of the operating abuse. Such is the nature of any manufacturing process, and we won’t know if we have great, less-than-great, or a mix of both in our cars until we start using them. Then, there are the great majority of cells that will stay healthy with minimal degradation if operated within certain conditions. How do we know what these conditions are? Tesla states them in the operating manual! Some cells may last longer (or die sooner) if treated differently, but nobody has more experience with EV batteries (or more terabytes of accumulated usage data) than Tesla. Modified or additional operating procedures may help or hinder battery longevity, but Tesla knows what matters most and gives us the advice based on their knowledge.

My plan, FWIW, if and when I get my MYP, is to drive it, follow the guidance in the manual as best can within practical limits, have fun, and fix it when it breaks (after shedding the mandatory tear, of course.)
 
Wait what? Charging above 50% harms the battery?
Of course it does. At least, it harms it more (as in causes more degradation than) charging only to 50%. If you want to minimize degradation (both calendar degradation and degradation from use) though, you have to keep the battery as close to 0% as possible as you can, without ever using it, and make sure that it doesn't get overdischarged. Of course, a battery that isn't used isn't very useful. You bought the car so you could use it. So if your goal is to minimize degradation, you should charge to as low a percentage as you can get away with, and charge as often as possible.
 
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Food for thought....

Charging Cycles Degrade Batteries​

Whilst the lithium-ion battery packs in electric cars constantly advance at a breakneck pace, repeatedly charging and discharging results in the degrading of EV batteries over time.

Geotab did a study on 6000 electric car’s battery deterioration and found that it will deteriorate at around 2.3% per year on average. This means if you bought a new Zoe today its 245-mile range would be reduced to around 189 miles after 10 years. Still far more than the average number of miles driven each week.

One of the main ways to prolong the life of your battery is to reduce the number of charging cycles your EV goes through. Don’t worry about plugging in each time you are near a charger. No matter if you are topping up your battery from 70% or when it is nearly empty, it still puts strain on the battery.
 
You're harming the long term health of your batteries if you're charging above 50% when you don't need to.
If you want to minimize degradation (both calendar degradation and degradation from use) though, you have to keep the battery as close to 0% as possible as you can, without ever using it, and make sure that it doesn't get overdischarged.

Ok, so charging over 50% harms the battery and to minimize degradation (which I infer to be the harm that I’m doing to my battery) I should keep it as close to zero as I can and not use it.

I must say this is rather unconventional advice and not what I was expecting when I started this thread.
 
Food for thought....

Charging Cycles Degrade Batteries​

Whilst the lithium-ion battery packs in electric cars constantly advance at a breakneck pace, repeatedly charging and discharging results in the degrading of EV batteries over time.

Geotab did a study on 6000 electric car’s battery deterioration and found that it will deteriorate at around 2.3% per year on average. This means if you bought a new Zoe today its 245-mile range would be reduced to around 189 miles after 10 years. Still far more than the average number of miles driven each week.

One of the main ways to prolong the life of your battery is to reduce the number of charging cycles your EV goes through. Don’t worry about plugging in each time you are near a charger. No matter if you are topping up your battery from 70% or when it is nearly empty, it still puts strain on the battery.
Wrong. One charging cycle = using and then replenishing the entire capacity of the battery. In other words, 100% to 0% to 100% is one cycle. 75% to 25% to 75% twice is also one cycle. 50% to 40% to 50% ten times is one cycle.

But here's the thing: the total number of cycles the battery can deliver is inversely related to the average depth of discharge (see Table 2). Deep charge and discharge cycles put extra strain on the battery and reduce the total number of cycles the battery can deliver so to prolong the life of the battery, you want to reduce average depth of discharge as much as possible and plug in whenever possible (but don't charge to high SoCs either unless you have to because that is also detrimental to the battery -- see Table 4).

In addition, storing batteries at high SoCs for long periods of time increases calendar aging, which saps capacity from your batteries even when they aren't being cycled (see the charts in this article). So in the event you need to charge your battery up to a high SoC, as you would before a road trip, you should aim to minimize the amount of time it spends up there, which means plug in and set the Scheduled Departure feature for about an hour before you expect to leave, and drive the vehicle immediately to get the SoC back down.
 
Ok, so charging over 50% harms the battery and to minimize degradation (which I infer to be the harm that I’m doing to my battery) I should keep it as close to zero as I can and not use it.

I must say this is rather unconventional advice and not what I was expecting when I started this thread.
Both High and Low SoC is bad for the battery. The ideal battery charge is around 50%. 0% SoC is likely worse than 100%.
 
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Both High and Low SoC is bad for the battery. The ideal battery charge is around 50%. 0% SoC is likely worse than 100%.
Definitely not. Lower is better, and 100% is by far the worst: ShieldSquare Captcha

The issue with going all the way down to 0% is that if they get overdischarged beyond a certain point, Li-ion batteries cannot ever be safely recharged again. Every li-ion battery contains some sort of protection circuit that makes it where, if the battery is discharged beyond a certain point, it won't ever be able to be charged again. So by storing batteries at 0%, you run the real risk of the batteries self discharging to the point where you lose 100% of the battery's capacity, rendering it useless. That's why people generally recommend that you store batteries between 40-60% SoC if you won't be using them for a long period of time.
 
being plugged in too long will just continue to "force feed" electricity into them until they explode in a fiery cataclysm and destroy the car and your house.

This might actually be true. It's happened to about a dozen Chevy Bolts. /s

--

No doubt there must be a non-technical component to this statement in the manual.

People tend to plug their cell phones in when they get pretty low... nobody charges at 85% (with only 15% down from full).

However, in most Teslas you're encouraged to set your charge limit somewhere between 50-90%. Mine is at 50. Running down 15% is a different story in this case. I'm over range anxiety though, so I'll happily drive in the single digits as long as there's enough juice to get there.

Plugging in always is just a good habit for humans, where charging takes hours if you forgot to plug in last night.

--

Also though... aren't these cars practicing active thermal battery management? If AC is used for preconditioning, might it also be used for thermal management of the battery?

Not sure how many charge cycles these types of activities might eat up over the lifetime of the vehicle, but that would be interesting to know. If the battery only averages 1500 cycles in its lifetime, maybe keeping it plugged in can save you 30 wasted cycles (I'm doubtful though).

My take on this whole thing: the pros of keeping it plugged in outweighs the cons.
 

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