Favor Low SoC or Small Cycles?

[AAKEE]

The Nissan LEAF experience does not confirm your guess -- quite the opposite. They have a veritable fleet of cars happily running around with degradation over 30%, and large numbers of cars with degradation over 50%.

The real issue is a few weak cells in the pack cutting off the range at low SoC. People who do not understand SoC and rely on the range estimators have the most confusion about practical range in these degraded cars but they run fine until they run out of range. Fine, as in they do not throw fault codes.

I think you missed a part of my post(-s)

What I am saying is that after passing 20% the degradation is not as predictable as before 20%. All research show this. Some continue to follow the predictable line, some does not.

For Tesla we have starting to see error codes that is not coupled to a faulty BMS or water leak but weak or shorted cells that make the continued charging not possible and makes the car need a battery change. So batteries fails, and they do it on the way we can expect.

Recently a model 3 in Sweden, that was supercharged with a high percentage and 200k km, developed short cuts in some cells making it need a battery change. Very expected that extensive Supercharging would lead to extensive lithium plating which in turn leads to short cuts in the cells.

 

[Hiline]

30% is a fair number for warranty reasons.
I think Tesla have chosen a good number there.

But this is not the same as that the batteries work fine down to 30%. Its not improbable that the battery pack start to give fault codes and work bad before reaching 30% degradation.

As the branch standard is not chosen randomly and the research tests shows just that ”unpredictability” after 20%: in some cases they work fine with the same degradation per time or cycle and in some cases they “loose it” I would recommend to for own personal limits try to stay out of degradations above 20%.

When the warranty period is over it would be very vice to be on the right side of the 20%-mark.
The market (people) will probably learn in the coming years and I believe in the future we will see cars that no one would like to touch.

We still can get unlucky and get a BMS failure or water leak or something, but I’m sure Tesla did learn from the weak spots and makes more solid packs, making tje risk for other failures lower.

A battery with good health will never be a burden when selling the car.

If the battery gets that dysfunctional after the warranty period, it can always be replaced. I believe the replacement cost is around $10k. Saying you wouldn’t touch a Tesla just because the battery degradation is past a certain level is a bit hyperbolic, I think.

 

[AAKEE]

If the battery gets that dysfunctional after the warranty period, it can always be replaced. I believe the replacement cost is around $10k. Saying you wouldn’t touch a Tesla just because the battery degradation is past a certain level is a bit hyperbolic, I think.

I think 10K is on the (very) low side.

When the net worth is low, a new batt is expensive.

 

[Hiline]

I think 10K is on the (very) low side.

When the net worth is low, a new batt is expensive.

And the cost is likely only going to go down.

When paying $10k gets you the equivalent of another car that runs for the next 10 years, I don't think this is expensive.

 

[E90alex]

And the cost is likely only going to go down.

When paying $10k gets you the equivalent of another car that runs for the next 10 years, I don't think this is expensive.

But you also have to figure that $10k is going into an already 10-15 year old car at that point which is going to be worn out mechanically and out of date technologically.

Figure if a Model 3 is worth $15-20k at that point plus $10k for a new battery, it makes little sense for anyone to spend $25-30k on a 10-15 year old Model 3 plus a new battery when they will likely have many options for a brand new $25-30k EV at that point with a full warranty and up to date technology.

 

[AAKEE]

The refurbished battery swap on a ’3 is somewhere about 15K.

The warranty is four years, quite expensive if it fail (any kind of issue) after that.

A ten year old used model 3 might not be worth that much so the 10K wont probably pay off.

 

[Hiline]

Maybe I'm not reading this correctly, but if the battery starts showing these fault codes don't you have to get the battery pack replaced in order to be able to keep driving the car? If so, the alternative would be to sell the car for scrap. If the scrap value is greater than the difference between a replacement car and a replacement battery pack, scrapping will be preferable. My thinking is that if a 10-year old Model 3 costs 20k, a replacement pack costs 10k, and the scrap value of such a car is 5k, I'll be better off paying for the replacement pack which should last much longer than a pack that comes with a replacement 10-year old Model 3.

 

[HMHM]

I am in a similar situation, charging to 56% (that is the inflexion point) and driving very short distances daily. I plug in when I feel like it or when I'm down around 40%. Mostly convenience really, as I don't particularly like to plug every evening. The difference is so subtle that it doesn't seem worth the hassle.

I have mainly accepted experts' analyses that show charging at 120V is quite inefficient. I also admit that there are some conservative members on the forum, who will keep their Teslas operating at an optimum range (less than 20% battery degradation) for a long period of time.

The metadata points to 3-4C charging rate as safe. Tesla NMC or NCA Li-ion batteries are engineered for 4C rate. It means that you can charge your 75 kWh battery safely at Tesla's 250KW V3 DC fast charging network without worry about the quick battery degradation. By offering an 8 year, 100,00 mi warranty, Tesla is literally banking on their analysis that a Tesla owner would not lose 30% of the range within the warranty period. If a degradation range of 20 to 29% is acceptable within 8Y/100,000mi, one may keep using the Supercharging network to 80 or 90% SoC, as recommended by Tesla. However, to keep the degradation to a minimum, I charge at home, using a TWC at 48A, 240V, limiting my supercharging sessions to occasional long road trips.

My Charging Best Practices:

Maintaining Li-ion Batteries - Real-world Recommendations for BEVs. The illustrated partial recharge cycle recommendations were revised recently in light of my extensive conversations with experts and long-time Tesla owners.

 

[AAKEE]

My Charging Best Practices:
View attachment 948022
Maintaining Li-ion Batteries - Real-world Recommendations for BEVs. The illustrated partial recharge cycle recommendations were revised recently in light of my extensive conversations with experts and long-time Tesla owners.

I do not agree on that chart.
Why do you use 30% as a ”low” value?

I see a risk of peoplecreading this as ”should not go below 30/20%”

Also, driving range without taking the type of road (highway etc) and the season wont keep the charging SOC as low as possible.

The type of car, size of battery and current degradation also affects the needed SOC.

The SOC charging level should rather be like *(Driving range x expected consumption / current available capacity) + a personal margin*

The above is how I do it.

I had two drives the two last days thats 162km back and forth, I drive 120km/h(75mph), the car usually uses 195-200Wh/km.
162x200/75000 + 10% = 53% so I did not change from the 55% usual level.
Ended up with about 13% both days which both I am fine with but also the battery.

Also, higher than 80% is not that bad so there is absolutely no reason to not use the battery range when needed.
A 100% charge at home will not cause as much wear as a extra supercharging stop.

I will post a answer about supercharging later.

So if we plan a long drive, 300km( 186miles) and we have a model 3 LR thats 3-4years its probably 10% degraded = 70kWh so usable about 67 kWh.
The LR might be slightly more efficient due to 18” than my car so I guess 180 Wh/km (290 Wh/mi).

300x190
Or
186x 290
= 54kWh

54/67 = 81%

Add a personal margin, taking the type of road and traffic and risk to have to stand in a que due to accidents etc.

For me, 90% would be good enough in more or less any case but I would probably still charge to 100% as its cool to see the current maximum range.

 

[AAKEE]

The metadata points to 3-4C charging rate as safe. Tesla NMC or NCA Li-ion batteries are engineered for 4C rate. It means that you can charge your 75 kWh battery safely at Tesla's 250KW V3 DC fast charging network without worry about the quick battery degradation.

I do not agree. You can supercharge but it will cause a higher degree of degradation.

The ”safe point” for Teslas NCA is about C/3 ( = about 25kW for model 3 LR)

These Panasonic NCA was about 2.9Ah, so 1A is about 0.3C. A higher charging rate will reduce the life /increase the degradation.

This test was not performed with preheated cells. The main issue with fast charging is lithium plating which in the long run causes internal short circuits.
From research we can see that preaheating is the best way to counter this issue.
Without preheating we will get extensive lithium plating and a shorter battery life.

LG’s M50 NMC that is used in ”rest of the world” for model 3 and Y do not like high currents at all.
These are a cyclic tests of the LG M50:
LG M50, low C is better
Another LG M50 low C is better

There is no question about that 0.3C causes less degradation than higher C-rates.

By offering an 8 year, 100,00 mi warranty, Tesla is literally banking on their analysis that a Tesla owner would not lose 30% of the range within the warranty period.

In the very most cases a car will not loose 30%.

For the lithium plating from fast charging I know of one model 3 that needed a new battery (out of warranty as above the miles limit). That car did not show more than about 12% degradation until several cells did brake down due to internal shorts. We know that the end state of lithium plating is cells that brakes due to internal short cuts.

There is a reason for Tesla advice.

I recemmend deeply to look into This research report. (Yes, it is in english, only the foreword or so is in german)
Many pages, but it covers most aspects in depth and all the results and conclusions is in line with most other research. They have a chapter about fast charging and supercharging.

The research shows that low SOC cycling can dissolve part of the lithium plating thus depleting some of the negative effects of supercharging, but except that part supercharging will cause increased wear on the battery.
Stating otherwise is going against all research and science, as I see it.

 

[Hiline]

I do not agree. You can supercharge but it will cause a higher degree of degradation.

The ”safe point” for Teslas NCA is about C/3 ( = about 25kW for model 3 LR)

These Panasonic NCA was about 2.9Ah, so 1A is about 0.3C. A higher charging rate will reduce the life /increase the degradation.

View attachment 948134

This test was not performed with preheated cells. The main issue with fast charging is lithium plating which in the long run causes internal short circuits.
From research we can see that preaheating is the best way to counter this issue.
Without preheating we will get extensive lithium plating and a shorter battery life.

LG’s M50 NMC that is used in ”rest of the world” for model 3 and Y do not like high currents at all.
These are a cyclic tests of the LG M50:
LG M50, low C is better
Another LG M50 low C is better

There is no question about that 0.3C causes less degradation than higher C-rates.

In the very most cases a car will not loose 30%.

For the lithium plating from fast charging I know of one model 3 that needed a new battery (out of warranty as above the miles limit). That car did not show more than about 12% degradation until several cells did brake down due to internal shorts. We know that the end state of lithium plating is cells that brakes due to internal short cuts.

There is a reason for Tesla advice.
View attachment 948154

I recemmend deeply to look into This research report. (Yes, it is in english, only the foreword or so is in german)
Many pages, but it covers most aspects in depth and all the results and conclusions is in line with most other research. They have a chapter about fast charging and supercharging.

The research shows that low SOC cycling can dissolve part of the lithium plating thus depleting some of the negative effects of supercharging, but except that part supercharging will cause increased wear on the battery.
Stating otherwise is going against all research and science, as I see it.

Thanks for sharing this study. The piece on the impact of temperature on degradation and the conclusion that shallow cycles only help when coupled with low SoC operation are fascinating.

But more importantly to me, if there even exist functional batteries with 2000 equivalent full cycles, which for a Model 3 LR equate to around 600k miles, perhaps the concern over longevity of modern HV batteries is a bit overblown. I don’t expect to keep any vehicle past 500k miles. 15 years of use is plenty for a non-commercial vehicle.

 

[AAKEE]

Thanks for sharing this study. The piece on the impact of temperature on degradation and the conclusion that shallow cycles only help when coupled with low SoC operation are fascinating.

But more importantly to me, if there even exist functional batteries with 2000 equivalent full cycles, which for a Model 3 LR equate to around 600k miles, perhaps the concern over longevity of modern HV batteries is a bit overblown. I don’t expect to keep any vehicle past 500k miles. 15 years of use is plenty for a non-commercial vehicle.

We need to look at the combination of calendar + cyclic aging and to stay away from >20% total to be sure that no problem develope (of course we can not protect us from broken BMS:es or water leaks etc).

 

[HMHM]

I do not agree on that chart.
Why do you use 30% as a ”low” value?

I see a risk of peoplecreading this as ”should not go below 30/20%”

I'm leaving a personal margin of 10%. I would try not to go below 20%, if feasible.

 

[HMHM]

I do not agree. You can supercharge but it will cause a higher degree of degradation.

We have limited choices when on a long trip! I'm not a proponent of Superchargering for routine local driving.

 

[AAKEE]

I'm leaving a personal margin of 10%. I would try not to go below 20%, if feasible.

There is no negative effect on the battery below 20% so there is no reason to stay above for the sake of the battery.

 

[tesluv108]

Tesla is not in the business of replacing batteries for free. Thus they have set the warranty criteria so that the vast majority of cars will not reach the 30% degradation threshold by the time warranty runs out. If they lowered that threshold to 20% they would likely have to replace significantly more batteries.

Right, you might as well have said “Tesla isn’t in the business of keeping customers happy”. There is no way these are designed to lose 30% within 7 years but it is designed to make Tesla replace less batteries. For long commuters it matters a 12% vs 25% degradation. For most others it doesn’t matter as much but it speaks to the quality of the battery in terms of customer perception

 

[tesluv108]

I still would like someone to comment on whether they think Tesla will allow my battery to run into 16 years of age without getting any errors? Calendar aging hasn’t seemed to have effected my battery at all as it’s only near 9k miles in 7 years. It was showing over99.5% health on Tessie. I think the previous owner used very conservative charging such as 75% max.

 

[AAKEE]

I still would like someone to comment on whether they think Tesla will allow my battery to run into 16 years of age without getting any errors? Calendar aging hasn’t seemed to have effected my battery at all as it’s only near 9k miles in 7 years. It was showing over99.5% health on Tessie. I think the previous owner used very conservative charging such as 75% max.

What car, year, model and battery etc?

Tessie often have the initial value showing something completely different than the stock battery capacity.

I guess we find that you are following the same route that other batteries does.

Calendar aging does not happen from bad luck or destiny. It can pe prognosed as it follows the laws of physics and chemistry.

 

[zazim]

This is incredibly useful for me (thanks AAKEE). I use 10% of my battery for my daily commute. I haven't gotten my Tesla wall charger installed so I am using the home AC charger. AC charging is very slow. It sounds like I should set my charge limit to 50% and wait until my car is at 20% to start charging again. If I can only add 10-15% with overnight charging, I should be able to charge daily and still keep my SOC in the 20-35% range during the week. I picked 20% as my threshold so that I would still be protected if charging fails during the night.

 

[E90alex]

This is incredibly useful for me (thanks AAKEE). I use 10% of my battery for my daily commute. I haven't gotten my Tesla wall charger installed so I am using the home AC charger. AC charging is very slow. It sounds like I should set my charge limit to 50% and wait until my car is at 20% to start charging again. If I can only add 10-15% with overnight charging, I should be able to charge daily and still keep my SOC in the 20-35% range during the week. I picked 20% as my threshold so that I would still be protected if charging fails during the night.

There’s not really much benefit from waiting until 20% to charge, especially if you only have 120V charging. It will take forever to get back up to 50% from 20%.