Myths and truths about the battery

[David99]

After 3 years driving my Model S I learned a few things about the battery and decided to make a video helping explain many things going on inside the battery. I really tried to keep it short, but ... oh well
I know there are some strong options and definitely some myths that keep getting repeated.

If you don't want to watch the whole thing and just want to know where my degradation is after 3 years and 115k miles:
I lost about 7% capacity. Acceleration seems unchanged. Supercharging is definitely slower than it used to be by aprox 15%.

 

[AnxietyRanger]

85 kWh battery with 15% slower Supercharging is an interesting reference point given the other discussion and effects of DC charging taper changes over time. Thank you for reporting.

So far the percentage talked about in DC charging incuded Supercharging peak rate throttling has been 8%.

 

[essmd]

I don't understand why some want to disagree and contest what Tesla is recommending regarding charging and battery health.

Nobody knows the science behind their battery packs and management software better than them.

Plus, Tesla and the owners are on the same side about maximizing battery life.

So...Plug in when at home, avoid the extremes, and slower charging rate is preferred unless convenience is at stake.

 

[AnxietyRanger]

Nobody knows the science behind their battery packs and management software better than them.

Plus, Tesla and the owners are on the same side about maximizing battery life.

While the former, I am sure, is true - the latter is obviously not true always from a potential conflict of interest perspective.

Tesla will always have business interests that can be opposite to the customer's interests. This means it is quite likely their recommendations will always be weighted on a scale with business interests on one side and other interests on the other side, whereas the average customer has no such business interests to consider. It is good that all customers keep that in mind when dealing with companies.

I think the DC charging recommendations are a good example of this. Tesla admits there is a small amount of batteries (customers) that can have their peak rates cut due to frequent DC charging use, yet they were not changing their recommendations to reflect this at all. IMO a very plausible reason, or at least a risk of conflict of interest, could be that they have business interests that would be opposite to such a recommendation. I mean, customer awareness on the risks of frequent DC charging could hurt the Supercharger story. Their Service Centers have been giving out the recommendation to avoid so much DC charging to some owners, but corporate seems reluctant to give even a vaguest of such warning.

I am not saying this is what Tesla is necessarily doing (and they might change their guidance tomorrow, for all I know, and I hope they do), but this potential conflict of interest will always remain between companies and customers.

 

[Max*]

Supercharging is definitely slower than it used to be by aprox 15%.

Are you talking about peak power or overall supercharging time?

If it's the former, how do you know that the 15% degradation in supercharging is due to the battery and not a change in the charging algorithm/taper that Tesla uses (which was speculated that it changed with one of the firmware updates)?

 

[Max*]

I got through about a third, I couldn't listen to the whole thing. You state a lot of "facts", but it's not scientific whatsoever.

"The difference between charging to 70% to 80% isn't that big", well how big is it?
"The state of charge is kind of lower", well how much lower is it? And how much difference does it really make? Is it negligible? If not, how much better is it?
You rehash the 90kwh battery thread, with a lot of speculation. Speculation != facts. "it seems" "I think" etc.
"At low temperature the degradation isn't so bad, at high temperature it is" Well, how bad is it? What's the delta?

 

[apacheguy]

How about you peak battery draw under wide open throttle? Noticed any decreases there? Of course this one is tricky as it depends on temperature and SOC.

 

[essmd]

While the former, I am sure, is true - the latter is obviously not true always from a potential conflict of interest perspective.

Tesla will always have business interests that can be opposite to the customer's interests. This means it is quite likely their recommendations will always be weighted on a scale with business interests on one side and other interests on the other side, whereas the average customer has no such business interests to consider. It is good that all customers keep that in mind when dealing with companies.

I think the DC charging recommendations are a good example of this. Tesla admits there is a small amount of batteries (customers) that can have their peak rates cut due to frequent DC charging use, yet they were not changing their recommendations to reflect this at all. IMO a very plausible reason, or at least a risk of conflict of interest, could be that they have business interests that would be opposite to such a recommendation. I mean, customer awareness on the risks of frequent DC charging could hurt the Supercharger story. Their Service Centers have been giving out the recommendation to avoid so much DC charging to some owners, but corporate seems reluctant to give even a vaguest of such warning.

I am not saying this is what Tesla is necessarily doing (and they might change their guidance tomorrow, for all I know, and I hope they do), but this potential conflict of interest will always remain between companies and customers.

And I though I was cynical and paranoid..

Well I would agree with you if there was a motivation by Tesla to benefit from battery degradation, as in profits to be gained from repair or replacement. But given the 8 years of warranty, I don't think Tesla considers that to be a source of revenue, and definitely a source of bad PR.

Regarding your point about different recommendations from corporate and service centers, I don't have that much experience to to confirm or deny, but undoubtedly one must consider the source of information carefully, for I have found that there is inconsistent information provided from every direction.

In general, the overall message from Tesla is:

1) Avoid the extremes charging status of the batteries
2) Keep the car plugged in when possible
3) Slower charging is preferred when convenient

Those are pretty much the general recommendations from all Tesla resources, more granular than that can be infiltrated with individual presumptions and opinions, diluting the reliability of the information.

 

[David99]

How about you peak battery draw under wide open throttle? Noticed any decreases there? Of course this one is tricky as it depends on temperature and SOC.

I didn't have the right equipment to measure it when I got the car new. I have been using TM-Spy for about a year now but since I have no exact data to compare it to, all I can do is compare my 0 to 60 times and they have not changed. But then we know measuing 0 to 60 is affected my several other things so it's not ideal to use it to compare.

 

[AnxietyRanger]

And I though I was cynical and paranoid..

I would say realistic.

It is not hard for me to see why a company might want to give different guidance than customers. Company wants to avoid costly recalls and adding purchase/adoption obstacles to future buyers. Brushing some things under the carpet might thus well be within a company's interests. Not saying they will necessarily do this, just saying this is an area where companies and consumers have a conflict of interest.

A conflict of interest, after all, does not require wrongdoing to exist. Much of the time noting it simply means the potential for wrongdoing is higher when there is a conflict of interest (that's why a judge will not get to judge a case involving their family, for instance).

 

[JasonA-EV]

In general, the overall message from Tesla is:

1) Avoid the extremes charging status of the batteries
2) Keep the car plugged in when possible
3) Slower charging is preferred when convenient

From what I've seen and tested (I've had TMspy since day 1) the notion of SpC'ing is "better" because it engages the active cooling system is totally false. People will take a cold battery, cram a ton of energy into it, then it sits all day either at home, the office or whatever at 100 to 110*f and does nothing else.

The active cooling doesn't work after that as the pack SLOWLY cools off during the day remaining hot and baking the cells (look at TMspy if you don't think so). If you L2 charge a cool pack from the start, it will never really get that warm and stays "cool" until it's done. There's such a big difference in temperature between L2 and SpC temps.

I can totally agree with those statements, and for someone who plans on keeping their S for a long time... that's a wise plan to consider!

And #1.. man ohh man, I don't get people who do 95% charge and then go down to red on their battery almost every time! And still wonder why they loose miles.

And people wonder why my Rav still has lost only 8 miles capacity after 63k

 

[alehbaba]

so with a new 60d whats the best plan? charge to 50/60.70/80/90/100%? I plug in every night at home. should i charge to 50-90% most times and 1-2x a month charge to 100%? or only charge to 100% when tAking a trip(maybe 2x a year?) or what?

 

[TexasEV]

Only charge to 100% when taking a trip-- but don't hesitate to do so if it's just a few time a year.
Hint-- that's why the battery charge slider says "trip" above 90%.

 

[David99]

so with a new 60d whats the best plan? charge to 50/60.70/80/90/100%? I plug in every night at home. should i charge to 50-90% most times and 1-2x a month charge to 100%? or only charge to 100% when tAking a trip(maybe 2x a year?) or what?

The new 60 is an exception because it is, as we know, really a 75 battery that is software limited to only charge 60 kW of energy. That's aprox 80% of the actual capacity of the battery. In other words, when you charge your new 60 to 100% you are really only charging it to 80% which is great for the life of the battery. Because of that you can charge your new 60 to 100% every day if you need without having to worry too much about degradation. Of course if you don't need the full range, it's good to set the charge slider lower. But it's not as important as it is with the other batteries that are not software limited.

As I said in the video, what really matters is the average state of charge over time. Say your battery is empty, you charge it to 100% and then start driving all the way down to empty again, over time, your average state of charge is only 50%. Just think about it that way. The more time you keep the battery at a high state of charge, the worse it is for the battery life. Charging it high and then start driving right away isn't a problem at all.

 

[Duke-U]

Very informative video, thank you !

 

[Viking1]

Not bad. From what I've read we should expect about 5% loss at 50K and 10% at 200k. How frequent is your supercharging?

 

[David99]

Not bad. From what I've read we should expect about 5% loss at 50K and 10% at 200k. How frequent is your supercharging?

Based on the data we have now, degradation is fast in the beginning and then slowing down. I have 118k now and 7%. Looking at my degradation over time I don't think I will be at 10% when I reach 200k. maybe 8 or 9%.

I use Superchargers very much. About 60% of all my miles are driving on Superchargers only. A total of about 600 Supercharging sessions. I also live in a pretty warm climate.