Does leaving a battery at low state of charge cause degradation or just inconvenience?

[J-a-x]

I have heard that leaving a Tesla battery at low state of charge for long periods of time will permanently damage the battery (similar to high state of charge), but I have also heard the opposite, that there's no harm to the battery itself at low state of charge, just a convenience issue due to the fact that it might temporarily drop even lower than you left it at due to cold temperatures (for example if parking a car with 10% remaining battery in Boston in the winter, it might be at 8% when you are ready to drive again), or due to phantom drain.

The Tesla manual tells you not lo leave your car below 20% state of charge for long periods, but does not state why (it may be just the convenience factor listed above, not permanent degradation). I've seen some studies showing no degradation at low state of charge but for all I know there could be other studies stating the opposite.

I know that low state of charge implies a large depth of discharge cycle once if you charge it up to 80, which I know is not good for the battery, but is the low state of charge during storage itself actually a problem?

Just curious if there's any consensus on this.

 

[LoudMusic]

How nerdy are you wanting to get on this?

The short answer is it won't hurt your battery significantly more than say storying at 20%.

The longer answer is, the further you deplete a battery beyond about 5%, the harder it is to charge it again. Once it's up to the 'good zone' it'll charge normally again. Some battery chemistries if they get even more depleted they may not charge at all.

Apparently, frequently using a bigger range of the capacity of the battery has a bigger effect on the battery life than any particular state of charge. So keeping it in the 40 to 80 range, for example, would likely be best for battery longevity.

 

[ATPMSD]

There are literally thousands on posts on subjects like this. Get a big pot of coffee and read the posts if you want to nerd out. Or just keep the SOC between 20% & 80% for daily driving and just enjoy the car.

 

[AAKEE]

I have heard that leaving a Tesla battery at low state of charge for long periods of time will permanently damage the battery (similar to high state of charge), but I have also heard the opposite, that there's no harm to the battery itself at low state of charge, just a convenience issue due to the fact that it might temporarily drop even lower than you left it at due to cold temperatures (for example if parking a car with 10% remaining battery in Boston in the winter, it might be at 8% when you are ready to drive again), or due to phantom drain.

The Tesla manual tells you not lo leave your car below 20% state of charge for long periods, but does not state why (it may be just the convenience factor listed above, not permanent degradation). I've seen some studies showing no degradation at low state of charge but for all I know there could be other studies stating the opposite.

I know that low state of charge implies a large depth of discharge cycle once if you charge it up to 80, which I know is not good for the battery, but is the low state of charge during storage itself actually a problem?

Just curious if there's any consensus on this.

Low SOC is not bad at all, so it is Tesla that tries to make sure we do not leave the car until it runs out of jiuce. Stuck cars is much more bad for the publicity than a slightly increased degradation from normally using high SOC.

You can see that low SOC is good, even down to 0%. This is for calendar aging. For cycles, it is not bad either.

 

[jefferrrson]

Low SOC is not bad at all, so it is Tesla that tries to make sure we do not leave the car until it runs out of jiuce. Stuck cars is much more bad for the publicity than a slightly increased degradation from normally using high SOC.

You can see that low SOC is good, even down to 0%. This is for calendar aging. For cycles, it is not bad either.
View attachment 1030425

So I drive to work weekly and it's about 20 miles and such and lately, i've been charging it up to 80%. I've always been intrigued with how batteries work in general (phones, charging cables, battery banks for video games/phones/tablets/laptops, everything lol) and i just got my Model Y Long Range last month so I want to really take care of the battery. I've watched endless amounts of YouTube and many other channels on this exact subject. I swear I should've been an electrical engineer lol but anyway, I see that you're very technical on this subject which I love bc i'm the same way.

Anyway, I guess my question to you is, in lamens terms, to sum several posts of yours, is to just charge the battery when I get home and not let it have longer charge times right? So let's say two scenarios.

Scenario A) I begin on Monday with 80% and then by Thursday i'm at 20%. Then I charge overnight from 20% to 80%.
or
Scenario B). Begin on Monday with 80% SoC, go to work, and drive back home and arrive with 70% of charge. Charge overnight from 70% - 80%.

Which scenario is better long term for the battery?

Knowing what I know, let's say phones, charging beyond 80% will degrade battery faster over time... but then again that's a whole different chemistry and all the above. Maybe i'll find the answer within your couple thousand posts. Thanks in advance sir.

 

[mborkow]

Charge to 50% daily. Drive to work and back arrive back home at 40% and charge back to 50% is best for your battery. Shallow discharge and keep it at 50%.

 

[ucmndd]

@jefferrrson , @mborkow nailed it. Charge daily. Keep the charge limit as low as you can to meet your needs (in your example 50% sounds like it would be fine).

You don’t say what model/battery you have but in any case an occasional charge to 100% would be fine too (helps the car calibrate actual capacity/range).

 

[jefferrrson]

@jefferrrson , @mborkow nailed it. Charge daily. Keep the charge limit as low as you can to meet your needs (in your example 50% sounds like it would be fine).

You don’t say what model/battery you have but in any case an occasional charge to 100% would be fine too (helps the car calibrate actual capacity/range).

how can i figure out what battery i have? I just got my 2024 Model Y Long Range last month lol. Actually been 32 days to be exact.. i know i'm probably splitting hairs but from what I read so far, I think charging to 50% is fine.. not too high not too low. And I guess making sure on the weekends (where I drive more often) I can charge to 80%.

Man i wish there was a few more studies on this or if these third party Tesla apps like Tessie and Stats could share data on the whole fleet. That would be great. I just learned about this whole calendar cycle thing vs cycle life aging or whatever it is. @AAKEE 's posts have been wonderful.

I still find it hard to believe that 0-10% is okay for the battery... just goes against all the principles that i've seen on lithium batteries outside of EV's such as phones/power banks. then again, we're talking about the largest battery a consumer can purchase so i'm sure it's a whole different playing field on that end.

 

[ucmndd]

Model Y LR in the US has Panasonic-sourced NCA chemistry cells in the 2170 form factor.

There’s really zero concern with low states of charge in terms of battery health and longevity. The only danger for lithium batteries is discharge “beyond zero” or a critically low voltage. In the case of a Tesla “0%” is actually not zero, there is a sizable buffer at the bottom of the battery to prevent any damage. A battery sitting at say 5-10%, even for indefinite periods provided it can’t discharge further, is perfectly healthy and happy.

 

[jefferrrson]

Model Y LR in the US has Panasonic-sourced NCA chemistry cells in the 2170 form factor.

There’s really zero concern with low states of charge in terms of battery health and longevity. The only danger for lithium batteries is discharge “beyond zero” or a critically low voltage. In the case of a Tesla “0%” is actually not zero, there is a sizable buffer at the bottom of the battery to prevent any damage. A battery sitting at say 5-10%, even for indefinite periods provided it can’t discharge further, is perfectly healthy and happy.

So I would be confident in that below 20% SoC but I watched this video of this Tesla Model Y owner who had his 12v battery go dead and I believe Tesla put the fault at user error for having the main battery pack below 20% so it wasn't "covered" ... That's what i'm avoiding to go below 20% due to this video and would hate this to happen to me.

-- let me know what you all think about this. perhaps his issue is a anomaly but man, that's not good.

 

[ucmndd]

So I would be confident in that below 20% SoC but I watched this video of this Tesla Model Y owner who had his 12v battery go dead and I believe Tesla put the fault at user error for having the main battery pack below 20% so it wasn't "covered" ... That's what i'm avoiding to go below 20% due to this video and would hate this to happen to me.

-- let me know what you all think about this. perhaps his issue is a anomaly but man, that's not good.

I didn't watch the video although I can imagine what it says. There's a lot of misinformation out there on Youtube and Tesla service people are well-known for kinda just making stuff up as they go.

That said,I can see a kernel of truth to the clickbait video title without watching it - Teslas DO engage in some protection behavior below ~20% state of charge to keep the main battery from discharging to a critical level. For example things like Sentry mode, cabin overheat protection, stuff like that stop working below 20% to minimize drain. There is some speculation that cars won't charge the 12v battery below a certain threshold either but I believe that to be unconfirmed and would be a stupid design choice at 20% state of charge (maybe less stupid at say 5%).

At any rate - I'm not advocating for keeping the car at a VERY low state of charge all the time. That's practically inconvenient. The lowest daily charge limit you can set is 50% and that works very well if you don't need more - you get basically all of the benefits of keeping the state of charge lower and none of the downsides.

If you can get by with 50% SoC for daily use that's what I'd do. Set the charge limit to 50% and charge every day. Bump it up for trips, weekends, or when you just need more juice.

 

[jefferrrson]

I didn't watch the video although I can imagine what it says. There's a lot of misinformation out there on Youtube and Tesla service people are well-known for kinda just making stuff up as they go.

That said,I can see a kernel of truth to the clickbait video title without watching it - Teslas DO engage in some protection behavior below ~20% state of charge to keep the main battery from discharging to a critical level. For example things like Sentry mode, cabin overheat protection, stuff like that stop working below 20% to minimize drain. There is some speculation that cars won't charge the 12v battery below a certain threshold either but I believe that to be unconfirmed and would be a stupid design choice at 20% state of charge (maybe less stupid at say 5%).

At any rate - I'm not advocating for keeping the car at a VERY low state of charge all the time. That's practically inconvenient. The lowest daily charge limit you can set is 50% and that works very well if you don't need more - you get basically all of the benefits of keeping the state of charge lower and none of the downsides.

If you can get by with 50% SoC for daily use that's what I'd do. Set the charge limit to 50% and charge every day. Bump it up for trips, weekends, or when you just need more juice.

understood. Thanks for the prompt reply and feedback! truly appreciate it for a Tesla noob like me! Been watching/researching for the past 3-5 years on Tesla and batteries so I take the advice very seriously. Thank you!

 

[AAKEE]

I still find it hard to believe that 0-10% is okay for the battery... just goes against all the principles that i've seen on lithium batteries outside of EV's such as phones/power banks.

Thats how myths work. Once you ”learned” it feels like you ”know”.

Like @ucmndd wrote, 0% is not completely dead.

The cells Tesla use in LR and P cars (Panasonic NCA and LG NMC) has 2.5 Volt as the stop discharge point, i.e 0% SOC.

These cells was made to be cycled 100-0%.
0% is set by the cell manufacturer as the stop discharge voltage.
100% is not the maximum possible charge level. It is possible to charge these to 130-140%. But the life would be short so the max charging level was set to a level that offers an acceptable life.
100% is 4.20V/ cell which is the branch standard.

If you had a lithium battery die, it sure went below 0%. The research shows that discharging below 0% is safe for small overdischarges so it is not critical if going past this slightly but draining the cell to 0V is not good.

Teslas 0% on the screen is actually 4.5% real SOC.

The main battery has the same “stop discharge” point as described above as the battery minimum voltage and the BMS shuts the battery of at or above that point to protect the battery if you drive until the cars stops (way beyond 0% on the screen).
From this point you can not consume any energy of the pack and it could be laying around quite long before it becomes a problem. Discharging cells to 0% makes them recover voltage when the load is taken away so the voltage will be higher after the battery has been at rest.
So, it is not bad for the main battery but it a problem as you are stuck and need to charge the car. If you leave the car like that the low voltage battery will drain as it get no charge and may get damaged if it is the old lead acid 12V type.

 

[AAKEE]

So I would be confident in that below 20% SoC but I watched this video of this Tesla Model Y owner who had his 12v battery go dead and I believe Tesla put the fault at user error for having the main battery pack below 20% so it wasn't "covered"

You need to read the manual.
20% is not the limit for this.
You are responsible to not let the car go beyond 0% and stop charging the low voltage battery which with the lead acid 12V type means that you need a new battery.
The new cars comes with a lithium low voltage battery that also shut down before they drain and damage. So in that case, no need to change the low voltage battery but it needs a specific action to wake up.

Its best not to go there where the main battery shuts down. The buffer below 0% displayed can be driven on but you do not know when the car stops.

If you have a new car (or ~2022 or newer) the car has the lithium ion low voltage battery.

Tesla tries to make us avoid ending up with the car stuck due to no energy. This is made by telling us to charge if the car has low SOC.

 

[J-a-x]

So it seems like I was correct that basically going below 20% isn't going to cause degradation but can increase the probability of others issues like complete discharge (it gets you closer to true 0% SOC which is truly bad), 12V battery issues (maybe), etc. So makes sense Tesla would steer people away from super low charge on a daily basis.

But if for example I arrived home late at night after a long trip at 10% SOC it wouldn't hurt anything to wait until morning to plug in. That's a common scenario for me. I have a shared HOA charging station at home so I never have a guarantee I can charge immediately after a trip. For those odd days I arrive home and somebody is using the charger, it seems like I can wait until morning without negative consequences and don't have to go find a supercharger in the middle of the night to avoid degradation. That's the type of scenario where I'd spend "some time" below 10%. I'd never store my car that way long term because it would be a huge pain if something came up and I had to drive somewhere. I rarely go below 20% except on long road trips for a well planned supercharging stop.

 

[byeLT4]

Just be careful. It seems at lower states of charge when the battery cools it likes to drop FAST. I remember being at work where I'm just 30 seconds from a supercharger and in 4 hours I dropped from 8 to 2 and was starting to get nervous

 

[J-a-x]

Just be careful. It seems at lower states of charge when the battery cools it likes to drop FAST. I remember being at work where I'm just 30 seconds from a supercharger and in 4 hours I dropped from 8 to 2 and was starting to get nervous

Yeah makes sense. I've not yet arrived anywhere but a supercharger with 8% luckily! I have gotten home with 10% though and let it sit overnight, then moved it 0.01 miles to the nearest L2 charger. I actually have a 120V outlet next to my parking space I could use in a pinch though technically my HOA forbids it (super annoying and too off topic to get into here but it would sure be nice to never have to think about leaving it overnight at low SOC).

 

[AAKEE]

Just be careful. It seems at lower states of charge when the battery cools it likes to drop FAST. I remember being at work where I'm just 30 seconds from a supercharger and in 4 hours I dropped from 8 to 2 and was starting to get nervous

I do not get it if you mean when driving or parked.

The displayed SOC is energy wise, so if it drops faster at low SOC during a drive, the BMS probably is off and overestimate the capacity.

If it drops from cold when parked, it is only the displayed SOC that drops. The measured SOC stays the same when the battery cools. So this is active choise from Tesla to reduce the displayed SOC when the batterybis cold. If ypu park with 10% and the battery cools and shows 5%, you still have 10% SOC, so no risk of shutting down and drain the LV Bat from that.

If the first point is valid, and the BMS overestimate the capacity, the real SOC is lower than the estimated during a drive so when parking and the car can read the real SOC (by measuring the cell voltage).
This causes a drop of the displayed SOC.

 

[byeLT4]

I do not get it if you mean when driving or parked.

Parked. I understand what you are saying. But I'm not going to trust it. It's not showing the blue cold battery capacity, that I would understand. I'm just stating that when 30-90% my car drops 0-2% normally, and closer to zero on average. But when I park with 10-15%, I lose around 6% on average and in a shorter period of time. I've never seen that percentage return when I start driving. I always assumed it was the battery low balancing.

 

[AAKEE]

Parked. I understand what you are saying. But I'm not going to trust it. It's not showing the blue cold battery capacity, that I would understand. I'm just stating that when 30-90% my car drops 0-2% normally, and closer to zero on average. But when I park with 10-15%, I lose around 6% on average and in a shorter period of time. I've never seen that percentage return when I start driving. I always assumed it was the battery low balancing.

I would say it is not balancing.

Balancing at low SOC causes imbalance at high SOC, so then you would need to counter the balancing that happend at low SOC when charged to high SOC.