With a mere 5% battery degradation, could it be possible that the buffer is released over time?

[Doug_G]

^ That survey doesn't put the hypothesis in hot water though. Just because there's little degradation, it doesn't prove there's no trickery involved.

There have been extensive discussions in the past. People have dug up data sheets for similar Panasonic Li-Ion batteries, which show the expected degradation curve. What Tom Saxton found was entirely consistent.

Some notes:

1. The rate of degradation correlated best to the number of pack cycles (equivalent complete charge/discharge cycles).
   
2. Mileage is a good proxy for pack cycles. It's not quite as accurate because energy is expended on other things like HVAC, and people have different driving habits.
   
3. There is no measurable correlation of degradation whatsoever with pack age.

I respect Tesla but am just wondering how they can make battery so right whereas with Nissan, you know what happened for the earlier Leaf's.

Simple. Leaf did no temperature management on their pack. Just some air flow. Tesla has a liquid cooled/heated pack that maintains the batteries withing their safe operating range. Batteries degrade faster when they are hot and at high state of charge. Avoid either of those situations and the degradation is much less. Avoid both and it is even smaller. Tesla keeps their packs cool and limits regular charging to 90%.

 

[Runt8]

... lost 20% or more range in 5-6-7 years.

Maybe I've missed it, but I haven't seen rash of Tesla's losing anywhere near that much, even going on > 10 years.

 

[arnis]

It appears Tesla's lose around 1% per year.
And other EV's around 2% per year.
My Leaf lost 6% in 3 years. Due to climate, I do not need thermal management.

It's unlikely that there is 5% or 10% buffer on Teslas with not limited battery pack.
There is no reason to have additional buffers. Users are taught to buffer themselves.
This is why 90% limit is there.
You don't want to get stranded because of buffer.

 

[David99]

The CAN bus data reports the buffer and it does not change over time on my 85. It would be a bad idea to eat into the buffer as it would degrade the battery only faster.

 

[David99]

1. There is no measurable correlation of degradation whatsoever with pack age.

I think there is plenty of evidence that age also degrades the battery.

Tesla keeps their packs cool and limits regular charging to 90%.

Actually it warms the pack to 30 C any time you drive it. If the ambient temps are already warm the battery will go up to 40C or more just from normal driving. Only when the battery reaches 50 C it starts to become active to cool. Saying Tesla is cooling their battery isn't really true.

 

[Doug_G]

I think there is plenty of evidence that age also degrades the battery.

In the data I've seen, there was no visible correlation with pack age. There was a very obvious correlation with mileage.

I'm not saying there's no degradation with age... I'm just saying it's very small compared to degradation with usage.

Actually it warms the pack to 30 C any time you drive it. If the ambient temps are already warm the battery will go up to 40C or more just from normal driving. Only when the battery reaches 50 C it starts to become active to cool. Saying Tesla is cooling their battery isn't really true.

The Model S lets the pack get a lot warmer than the Roadster did; it uses different chemistry that is somewhat more temperature tolerant. It's quite obvious that this temperature isn't causing excessive degradation because, plainly put, the packs don't degrade very fast.

Most laptop computers have a nice hot processor in there, the batteries are always charged 100%, and they're getting roasted. That's what kills the lifetime.

 

[Science fan]

Is it really possible to have that small a battery degradation over four/five years? Doesn't that kinda defy physics/chemistry?

Perhaps Tesla slowly releases the capacity buffer say from 20% down to 15 then to 10%?

Thoughts?

It might as well supply batteries to competitors once it gets its assembly in order.

Many 'S' owners write of losses of up to 5% in the first year, followed by 1% per year for a few years, and the belief that the pack then becomes stable for an unknown number of years. I have been driving my S75 for 18 months and have 15,000 miles on it. So far, there has been a 2% loss in capacity and I plan to keep "Joules" for 12-14 years. Hopefully, with the same battery pack. Replacement will be another Tesla of some sort. My understanding is that "Tesloop" put more than 200,000 miles on each of their cars in less than two years and they lost only 6% of capacity in that time. If I recall correctly, their battery packs were replaced at no cost by Tesla for a reason other than battery degradation. It seems very likely to me that the Model 3 batteries will be superior to those in my 'S' and degradation may be even more gradual.

 

[David99]

I'm not saying there's no degradation with age... I'm just saying it's very small compared to degradation with usage.

Tesloop has 300k miles and 6% degradation. My car has 138k miles and has 9% degradation. Both drive in the same area, both Supercharge a lot. What's the difference? My car is older.

 

[arnis]

I'm not saying there's no degradation with age... I'm just saying it's very small compared to degradation with usage.

Actually there is more degradation with time rather than with mileage.
Finnish taxi that has 400 000km and lost 7% is a prime example that mileage isn't that important.
That's 250k miles. Car from 2014.
As we see, mileage hardly matters at all. It's the state of charge and time and temperature.

 

[deonb]

Tesla keeps their packs cool and limits regular charging to 90%.

Nissan also recommends not charging to 100%, but they give you no practical way of doing that.

But you have to have your battery inspected every year, and if you let it charge to 100% all the time, they "ding" your record. Not exactly sure what happens with these dings, but it can probably void your warranty eventually.

It might have been a sensible policy if they had a way for the car to not charge itself over 90%!

 

[arnis]

they "ding" your record. Not exactly sure what happens with these dings, but it can probably void your warranty eventually.

No.

PS: Tesla 100% is more than Leaf 100%.

 

[Doug_G]

Actually there is more degradation with time rather than with mileage.
Finnish taxi that has 400 000km and lost 7% is a prime example that mileage isn't that important.
That's 250k miles. Car from 2014.
As we see, mileage hardly matters at all. It's the state of charge and time and temperature.

For insightful analysis of actual hard data, please view:

Battery Survey Results – Tom Saxton

 

[arnis]

At 10:50 he says Tesla does a great job keeping the pack healthy and "keeping the temperature".
This is wrong assumption. But overall, nice analysis.
Tesla's chemistry "accelerated degradation" starts at much higher temperature compared to 2011 Leaf.