Battery aging / degradation over time

[Polly Wog]

In your example that would mean charging to say 50% and driving 20 miles down to 40-something %

I respectfully disagree with only charging to 50%. I've been following the charging threads for a while now, and the majority of the data I've seen indicates that those of us who have consistently charged to 90% have maintained more of our battery capacity than those who consistently charged to less than 80%.

 

[Johan]

I respectfully disagree with only charging to 50%. I've been following the charging threads for a while now, and the majority of the data I've seen indicates that those of us who have consistently charged to 90% have maintained more of our battery capacity than those who consistently charged to less than 80%.

This is likely a calibration issue. All science regarding Li-ion shows that with low use cases staying in a lower voltage range is better. There is really no reason why it would be different in a Model S. The caveat of course is if you, by staying in a low voltage range, often dip in to the very low voltages which in itself can cause degradation. But for arguments sake I'm positive that daily driving between 50-40% SOC is better for battery longevity than the same amount of driving but staying between 90-80% SOC.

 

[qwk]

This is likely a calibration issue. All science regarding Li-ion shows that with low use cases staying in a lower voltage range is better. There is really no reason why it would be different in a Model S. The caveat of course is if you, by staying in a low voltage range, often dip in to the very low voltages which in itself can cause degradation. But for arguments sake I'm positive that daily driving between 50-40% SOC is better for battery longevity than the same amount of driving but staying between 90-80% SOC.

Of course daily driving between 40-50% is going to be better than 80-90%. No secret there. The unknown here is the fact that Tesla tries everything it can to keep the cells at the same voltage, temp etc., so that they age very similarly. When you USE the pack between 40-50%, the cells are not going to be at close to the same voltage for very long, because the pack has to balance to stay close to the same. Now the only question is, which is worse? The unbalanced pack used at lower charge levels, or the balanced pack used at higher charge levels?

I will tell you that getting an older Model S pack back into balance is very tough. Like a month's worth of charging to 100% tough.

 

[apacheguy]

The pack can balance at any SOC regardless of whether it's charging or idling. Each module contains a BMB with bleed resistors for this purpose. I question the idea that charging to 50% will be worse for balancing than 90%.

 

[qwk]

The pack can balance at any SOC regardless of whether it's charging or idling. Each module contains a BMB with bleed resistors for this purpose. I question the idea that charging to 50% will be worse for balancing than 90%.

Yeah, ok.

If that was the case, everybody's max charge numbers would be close to the same. They are not even close....

 

[apacheguy]

Not necessarily. That suggests it is a range algo calibration issue. There is no evidence to suggest this is a balancing issue.

 

[Troy]

We have actually data about daily charge level but it is inconsistent. The following table is from the same survey I mentioned above (Click HERE and go to stats page). According to this table 24 people said they charge to 80% daily. 20 out of those 24 are above the red line that we saw earlier. That means 83.33% of people who charge to 80% are doing better than average in terms of degradation. Interestingly this number is lower if daily charge level is 90% or 70%. I don't have any explanation for this but 80% appears to the best option.

 

[qwk]

Not necessarily. That suggests it is a range algo calibration issue. There is no evidence to suggest this is a balancing issue.

If it was a calibration issue, a couple of 100-0-100 charges would take care of it. They don't. If you don't believe me, set the slider to 100% for a while. It will get close to 265 RM. This is very old news, most people here just don't pay attention.

 

[Max*]

We have actually data about daily charge level but it is inconsistent. The following table is from the same survey I mentioned above (Click HERE and go to stats page). According to this table 24 people said they charge to 80% daily. 20 out of those 24 are above the red line that we saw earlier. That means 83.33% of people who charge to 80% are doing better than average in terms of degradation. Interestingly this number is lower if daily charge level is 90% or 70%. I don't have any explanation for this but 80% appears to the best option.

If you put error bars on that 70% SOC, it'll overlap with the 90% SOC and likely overlap with the 80% SOC. I wouldn't draw any hard conclusions from this.

 

[Cyclone]

It's hard to determine one way or the other b/c we do not have accurate data, even for our own cars.

I purchased at my car just under 31k miles. It charged 90% to 239 miles. That level went down until 90% was only 225 miles a couple months later, with me regularly changing to 85%. However, my battery needed to have the contactors replaced and it failed some "evacuation test" in the cooling system and was sent back to Freemont for refurbishment.

Since my original battery has been put back in my car, it was gone from 238 miles @ 90% to 239 miles @ 90% to 241 miles @ 90% in 3 days. This type of variability makes its very difficult to discern any pattern. Additionally, my SvC didn't disclose if any of my pack's cells were replaced/refurbished in California. So I don't know if things just got recalibrated while out of the car, the car is overestimating until its calibrated on the current pack, or the battery was refreshed through the repair process to be like-new.

 

[Polly Wog]

I agree that we as owners don't have enough data to know conclusively the best charge percentage. However, Tesla has a ton of data, and they recommend 90% for daily charging. For myself, that is what I'm going to continue to do.

 

[jerry33]

I agree that we as owners don't have enough data to know conclusively the best charge percentage. However, Tesla has a ton of data, and they recommend 90% for daily charging. For myself, that is what I'm going to continue to do.

Question: Where do they recommend it? I've never seen it in writing (Of course, I could have missed it.) Saying that "The Service Centre said so", doesn't cut it because if you ask at ten different SCs, you'll get somewhere around ten different answers.

 

[Max*]

Question: Where do they recommend it? I've never seen it in writing (Of course, I could have missed it.) Saying that "The Service Centre said so", doesn't cut it because if you ask at ten different SCs, you'll get somewhere around ten different answers.

That's a good point. The recommended for daily driving is 50%-90% (based on the battery icon in the car, and may even say recommended range, I don't recall). Above 90% is considered a trip charge, and not recommended to do all the time.

 

[Polly Wog]

Question: Where do they recommend it? I've never seen it in writing (Of course, I could have missed it.) Saying that "The Service Centre said so", doesn't cut it because if you ask at ten different SCs, you'll get somewhere around ten different answers.

So, when I got my Model S, there were two charging options available from the console: Daily (90%) and trip (100%). Although we have more options now, that is what I'm going off of. Of course, I used Visible Tesla to set it to points in-between, but almost never charged to less than 90%. @jerry33, you are of course correct in that Tesla has not given us a definitive answer on the best charge percentage, which is one of the reasons we owners are left to speculate so much on our own. I will concede the point you make. However, since I have only lost 1 rated mile in 18 months and 22,000 miles, I'm sticking with 90%.

 

[David99]

It is a well known fact that a lower state of charge will lower battery aging. There is nothing different about the Tesla that would magically make it better for the battery to be charged to 90%. That's exactly why the slider goes down to 50% and not just to 90%.

We don't know for sure when exactly balancing is happening. We do know that balancing isn't a permanent capacity loss. It is a temporary issue that can be fixed. So even if charging to a lower level results in less balancing, it isn't something you would worry about. Permanent degradation is, though.

 

[Todd Burch]

It is a well known fact that a lower state of charge will lower battery aging. There is nothing different about the Tesla that would magically make it better for the battery to be charged to 90%. That's exactly why the slider goes down to 50% and not just to 90%.

We don't know for sure when exactly balancing is happening. We do know that balancing isn't a permanent capacity loss. It is a temporary issue that can be fixed. So even if charging to a lower level results in less balancing, it isn't something you would worry about. Permanent degradation is, though.

Correct, but with one caveat--if a pack is significantly unbalanced, this stresses some cells (those with a lower SOC) more than others when power is demanded.

 

[lloyds]

Looks like my + matches the data.
100% @ 250 miles
85k miles
2.4 yr ownership
Daily SOC @ 50%-80%
Supercharge once a wk

 

[mknox]

My 100% is 242 Rated Miles. A-Pack, March 2013 car with about 60,000 miles. I did see a big drop, then it tapered to nearly flat for the past 10 to 12 months.

 

[djp]

I agree that we as owners don't have enough data to know conclusively the best charge percentage. However, Tesla has a ton of data, and they recommend 90% for daily charging. For myself, that is what I'm going to continue to do.

No, Elon recommends 80%. Here's the tweet.

Twitter

 

[apacheguy]

Now someone needs to ask what about 80-40% or 70-30%. I'm seeing my numbers slip when daily charge <80%. Might need to do a couple 90% but it's so hot these days and I don't drive enough to need that range.