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Leaving the car at 0%
- Thread starter ngng
- Start date
shahryaran
Member
beatle
Active Member
Found this on the internet:
"lithium-ion cells undergo unwanted chemical reactions when discharged below 3 V, causing their internal resistance to be permanently and significantly raised. Their capacity will suffer as well, meaning that they won't accept the same amount of charge anymore. When such an over-discharged cell is "brought back to life", it will likely become chemically unstable, creating a risk of a short circuit developing inside the cell."
That sounds about right. I am not sure what the individual cell voltage is when the pack reads 0%, but that would be the issue if it is below 3v. The good news is that there really isn't any HV drain at that point. The 12v battery will no longer get a top up and will eventually not be able to close the HV contacts, so the pack will be isolated from the car and will not drain further. Before that, the drain on the battery would be incredibly low at a per-cell basis so the battery should fade away and not burn out. This makes me think the car could possibly sit for a few months at "0%" without significant damage before you bring it back to life by plugging it in and jumping the 12v. There are others who have more experience here though.
"lithium-ion cells undergo unwanted chemical reactions when discharged below 3 V, causing their internal resistance to be permanently and significantly raised. Their capacity will suffer as well, meaning that they won't accept the same amount of charge anymore. When such an over-discharged cell is "brought back to life", it will likely become chemically unstable, creating a risk of a short circuit developing inside the cell."
That sounds about right. I am not sure what the individual cell voltage is when the pack reads 0%, but that would be the issue if it is below 3v. The good news is that there really isn't any HV drain at that point. The 12v battery will no longer get a top up and will eventually not be able to close the HV contacts, so the pack will be isolated from the car and will not drain further. Before that, the drain on the battery would be incredibly low at a per-cell basis so the battery should fade away and not burn out. This makes me think the car could possibly sit for a few months at "0%" without significant damage before you bring it back to life by plugging it in and jumping the 12v. There are others who have more experience here though.
Interesting. I over what duration that permanent damage occurs. I ask because I sold my X to Carvana and have been watching the SOC decline. It's been at 0% for a few days now
Correction:
Since that's a really expensive vehicle that's going to end up purchased by someone else, the nice responsible thing to do would be to contact someone there and tell them to charge it.
Maybe stop checking it. I believe you can remove it from the app yourself. That would remove the temptation to keep waking it up.
Since that's a really expensive vehicle that's going to end up purchased by someone else, the nice responsible thing to do would be to contact someone there and tell them to charge it.
Maybe stop checking it. I believe you can remove it from the app yourself. That would remove the temptation to keep waking it up.
Go to the lot and ask to test drive the car.Interesting. I over what duration that permanent damage occurs. I ask because I sold my X to Carvana and have been watching the SOC decline. It's been at 0% for a few days now
The entire reason I sold the car to them was so I didn't have to deal with it or CL tire kickers. It's their car now, I'm not going to tell them what to do.
I also don't use the app or check on the car, but I do see it when I switch car profiles in Tessie I see the battery declining in the UI.
ucmndd
Well-Known Member
israndy
Supercharger Hunter
Yeah, I might wanna correct you here. If you have evidence of what you state please present it, but I had a ton of those batts in my electric motorcycle that I let go low and it killed them dead. I would suggest caution.
Should this be "well ABOVE real zero"? Or do I misunderstand?
bo3bdar
Member
I'm sorry, but this is absolutely incorrect. ALL batteries have self-drain, there is nothing magical about LiIon chemistry or Tesla manufacturing that can change that. If this were true, you'd be able to fire up that laptop in the closet that's been sitting for 5 years, and you can't.
In LiIon batteries that self-drain is very low, especially when discharged, but it is never zero. In doing a bit of research it looks like it can be as low as 0.5%/month on an open circuit.
In a big pack like a Tesla, it's not likely to ever be open-circuit, because the Battery Management System will be monitoring all the cells, and trying to keep things balanced. Tesla might have some software tricks to disable this at zero, or might not. But otherwise it's going to be a larger drain. Best guesses here seem to be maybe 1%/month on Tesla packs.
Big Clive did an actual experiment to see how far you can push it, and found he could go to -10% before the battery was unrecoverable. At low charge levels you get internal copper dendrite growths, that can short and cause fires.
Putting those together, and you have maybe 10 months at 'zero' before the pack is unrecoverable. Lots and lots of variables and unknowns, but we can say it's months, not days or years.
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Watts_Up
Well-Known Member
I ask because I sold my X to Carvana and have been watching the SOC decline. It's been at 0% for a few days now
The following is just a personal assumption:
When the car is just seatting on a parking lot, the car will be in sleeping mode.
The 12V battery will be used by some components, such as the cellular connection and bluetooth devices.
And every few days, the DC/DC inverter will be activated to recharge the 12V battery.
With 0% Soc, or so, the DC/DC inverter might not be running any more (by design)
when the voltage of the cells of the propulsion battery are too low.
So the 12V battery then will be drained, and the car will be dead, I mean no possibility to open a door.
The only way to reactivate the car will be to connect a 12V charger and recharge the battery.
This will allow then to restart the car and in particular, be able to re-open the doors.
If the lead acide battery have been discharged too low and for too long (typically 50% of the capacity)
the 12V battery might not keep the charge and would need to be replaced.
Regarding the high voltage propulsion battery, since the 12V relay isolating the high voltage battery could not be activated,
this high voltage battery would not be discharged anymore and would still be around 0%, I mean what ever the low buffer value was set to.
So basically, this high voltage battery would not have been drained and would then stay with the same SoC for a very long time.
It is possble that the BMS monitoring the cells might eventually discharge the battery.
The only issue would be if the ambient temperature was below zero degree Centigrade because the battery could not be charged.
Trying to charge the battery below zero woud damage the battery, but I imagine that the Tesla high voltage charging would prevent it,
Also, it is possble that Tesla still try to keep the battery temperature to a minimum, but might stop doing it below 0%.
What I am wondering is if your car may have a 12V battery or a 16V Lithium-ion battery, because this 16V battery migh be dained
completely, unless there is maybe a static relay preventing it, and so this 16V Lithium-ion battery might be damaged,
and I wonder if would be even safe to recharge it?
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ucmndd
Well-Known Member
ucmndd
Well-Known Member
We are essentially saying the same thing, my post was worded poorly.
It’s my understanding the pack does go entirely open circuit at low states of charge to preserve itself as long as possible. This is essentially what happens when the LV system shuts down and the contactors are open.
Dendrite formation happens when a battery is entirely discharged, to the “bricking point”. Ingineerix had a good video on this a while ago - the Tesla 16v lithium low voltage battery actually has a MOSFET in it that prevents recharge if it’s ever completely drained to prevent fire.
I didn’t mean to imply a battery can sit indefinitely without ultimately discharging to a damaging/unrecoverable level. What I was trying to say is that there’s no inherent damage from a battery being maintained at a very low (but above 0%) state of charge. A battery sitting at say 3-5% state of charge is perfectly happy and there’s no cell damage or concern to speak of.
I know very little about the HV system, but wouldn't the HV have the potential to further discharge towards true 0 if there was an imblance between cell voltage, i.e. a stronger cell vs weaker?
As far as the LV battery, it's the legacy X so it's 12V.
israndy
Supercharger Hunter
Your wording is still gonna have some hapless individual think walking away from an EV that is fully discharged is a normal state of affairs, and it is not. If you put some qualifications in like 5% is fine for a week I wouldn't disagree with you, but self discharge is real and entirely dead battery are VERY expensive to replace.
Especially if someone worried about the battery keeps checking it's status by launching the Tesla app, it is only gonna make things worse.
There’s many faulty statements in the thread so I even do not know where to begin. It might be easier to not quote a single post and just post the correct statements
1) Lithium ion batteries are very happy at 0% SOC. In fact, they like it best at 0%. More on that, with proofs later.
2) 0% SOC is not completely empty but the voltage where the manufacturer say discharge should be stopped.
100% is the point where the charge should be stopped. Its possible to charge well above 100%, and to discharge below 0%.
Discharging past/below the discharge limit (0%) is called overdischarge. More on that later.
3) As voltage drops during load, a cell that is discharge to 0% actually recover voltage afterwords. The self discharge is very low on lithium batteries at low SOC and at 0% there is virtually “none”, as the voltage increases and stay higher for very long time.
4) Tesla use 4.5% buffer below 0% displayed so reading 0% is very long way from overdischarge. Teslas disconnect the HV battery well below 0% displayed but above the lover voltage limit ie before reaching the discharge limit. After disconnection there are no load on the battery and no energy is drawn from the battery.
5) The Panasonic NCA cells Tesla use has 2.5V as the end of discharge point, and 4.2V as the stop charging point (100%). At 0% we still are above 3.0V. The minimum pack voltage value we can read from the BMS correlates exactly to the 2.5V/cell.
This picture is from a real life test research report with cells taken from a almost new Tesla model S:
We can see a trend of lower SOC causing less calendar aging. But only 4 points in that test.
Another test, 0% included. The degradation during the first five months of calendar aging. Still Panasonic NCA (NCR19650) but not tsken from a car.
A third test, same type of cells as above:
This behavoiur is valid for more or less *any* research report. The sum of all research could be seen as the picture above. If we take the data from any research test it mostly match these numbers very close.
It woukd be easy to spam the tgread with other research showing the same thing, but I hope these three pictures can speak for virtually hundreds of research reports.
I have not found any report showing the opposite.
We can clearly see that 0% causes the lowest degradation from time. In these tests they most often charge/cycle the cells after about each 2-3-4 months to measure the capacity.
For overdischarge, which we can not do in a Tesla as the battery disconnects before this happens, there is research as well.
Summarized, for ”mild” overdischarge which would be to discharge the cell to about half the end of discharge voltage, by principle nothing happens. If you do it time after time after time, there can be seen a slight extra degradation in capacity. Doing it again and again will show a slight difference in degradation to the cells that was stopped on the limit, but this is mostly cyclic wear we see.
Going further than below half the discharge voltage and downto zero volts (completely dead) is not good, but damage the cells more om a random basis.
To the left, discharged as per the manufacturer limit. Second next to the left, discharged to about 50% of the end of discharge voltage. Only a slight extra degradation, after doing it about 140 times.
We do not need to be afraid of low SOC for the sake of the HV-battery. But when the HV-batt disconnects it stops charging the LV-battery (lead acid 12V, or lithium 16V in the later Teslas). These do not like to be discharged completely. In the 12V lead acid case, these are sensitive to being discharge (about below 50% is not good for them abd in case of the 16V lithium batt there is no low voltage protection so it will drain below the end of discharge limit if the car is not charged or the LV-battery disconnected).
1) Lithium ion batteries are very happy at 0% SOC. In fact, they like it best at 0%. More on that, with proofs later.
2) 0% SOC is not completely empty but the voltage where the manufacturer say discharge should be stopped.
100% is the point where the charge should be stopped. Its possible to charge well above 100%, and to discharge below 0%.
Discharging past/below the discharge limit (0%) is called overdischarge. More on that later.
3) As voltage drops during load, a cell that is discharge to 0% actually recover voltage afterwords. The self discharge is very low on lithium batteries at low SOC and at 0% there is virtually “none”, as the voltage increases and stay higher for very long time.
4) Tesla use 4.5% buffer below 0% displayed so reading 0% is very long way from overdischarge. Teslas disconnect the HV battery well below 0% displayed but above the lover voltage limit ie before reaching the discharge limit. After disconnection there are no load on the battery and no energy is drawn from the battery.
5) The Panasonic NCA cells Tesla use has 2.5V as the end of discharge point, and 4.2V as the stop charging point (100%). At 0% we still are above 3.0V. The minimum pack voltage value we can read from the BMS correlates exactly to the 2.5V/cell.
This picture is from a real life test research report with cells taken from a almost new Tesla model S:
We can see a trend of lower SOC causing less calendar aging. But only 4 points in that test.
Another test, 0% included. The degradation during the first five months of calendar aging. Still Panasonic NCA (NCR19650) but not tsken from a car.
A third test, same type of cells as above:
This behavoiur is valid for more or less *any* research report. The sum of all research could be seen as the picture above. If we take the data from any research test it mostly match these numbers very close.
It woukd be easy to spam the tgread with other research showing the same thing, but I hope these three pictures can speak for virtually hundreds of research reports.
I have not found any report showing the opposite.
We can clearly see that 0% causes the lowest degradation from time. In these tests they most often charge/cycle the cells after about each 2-3-4 months to measure the capacity.
For overdischarge, which we can not do in a Tesla as the battery disconnects before this happens, there is research as well.
Summarized, for ”mild” overdischarge which would be to discharge the cell to about half the end of discharge voltage, by principle nothing happens. If you do it time after time after time, there can be seen a slight extra degradation in capacity. Doing it again and again will show a slight difference in degradation to the cells that was stopped on the limit, but this is mostly cyclic wear we see.
Going further than below half the discharge voltage and downto zero volts (completely dead) is not good, but damage the cells more om a random basis.
To the left, discharged as per the manufacturer limit. Second next to the left, discharged to about 50% of the end of discharge voltage. Only a slight extra degradation, after doing it about 140 times.
We do not need to be afraid of low SOC for the sake of the HV-battery. But when the HV-batt disconnects it stops charging the LV-battery (lead acid 12V, or lithium 16V in the later Teslas). These do not like to be discharged completely. In the 12V lead acid case, these are sensitive to being discharge (about below 50% is not good for them abd in case of the 16V lithium batt there is no low voltage protection so it will drain below the end of discharge limit if the car is not charged or the LV-battery disconnected).
Well, no.
This is data from calendar aging tests on Panasonic NCA (NCR18650)
IR (AC)
IR (DC)
So, if you’re afraid of Internal resistance, have the cells at LOW SOC.
As per my last post above, this is only two examples of a lot of research showing about the same thing.
The chart at 16 minutes comes from a flawed research report.
( I did not look at the whole video).
That chart comes from a research report refering to Dynamic Stress Cycles (DST).
These can not be compared like in that chart.
Any reference to cyclic aging should use Full Equivalent Cycles (FCE) as they are directly proportional to the number of miles the car can do (for a certain degradation loss for example). “thoughput” in Amp-hours can oalso me used but is less common. Better to stick to the FCE.
The result in that chart can not be used without recalculation to FCE, to be comparable.
Which, in terms of the HV Battery is fine!Interesting. I over what duration that permanent damage occurs. I ask because I sold my X to Carvana and have been watching the SOC decline. It's been at 0% for a few days now
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