Lowering Amps to Improve Battery Life

[jgs]

I believe the Mobile Connector is meant as just that -- something that lives in the car in case it is needed. I don't think it is designed for constant/daily home charging.

As you probably know your belief is not shared by quite a few owners, nor does Tesla discourage use of the UMC this way. Indeed, the guidance I got from Tesla staff when buying my car was to use the UMC and save my money by skipping the HPWC.

I've been using my UMC for nightly charging for going on two years now with no drama.

 

[mal_tsla]

As you probably know your belief is not shared by quite a few owners, nor does Tesla discourage use of the UMC this way. Indeed, the guidance I got from Tesla staff when buying my car was to use the UMC and save my money by skipping the HPWC.

I've been using my UMC for nightly charging for going on two years now with no drama.

There's a secondary concern with using the UMC as a daily charger surrounding frequent plug/unplug wear on the NEMA 14-50 outlet, but that's irrelevant to the subject of this thread.

I just didn't want to discount people's experiences with their UMC getting hot as a possible motivation for charging their car more slowly than possible. That may in fact be a valid thing to do -- I don't have much experience with it.

 

[Rocky_H]

Nearest supercharger is about 100miles away. I definitely envy those of you with that extra flexibility that you can hope to encounter one on any random trip, but I bet it's the minority case.

Well yes, which is why I was suggesting people evaluate their own situations rather than the emphatic "always do this" type of blanket recommendations you were giving.

 

[Rocky_H]

There's a secondary concern with using the UMC as a daily charger surrounding frequent plug/unplug wear on the NEMA 14-50 outlet, but that's irrelevant to the subject of this thread.

But people who are settling on using the UMC as their daily charging solution sure as hell aren't plugging and unplugging it every day.

 

[jgs]

There's a secondary concern with using the UMC as a daily charger surrounding frequent plug/unplug wear on the NEMA 14-50 outlet, but that's irrelevant to the subject of this thread.

To continue the tangent -- this only matters if you take your UMC with you whenever you leave the garage, something I think few people do. (I certainly don't, I never take it except on road trips and even then it's seldom used.)

I just didn't want to discount people's experiences with their UMC getting hot as a possible motivation for charging their car more slowly than possible. That may in fact be a valid thing to do -- I don't have much experience with it.

OK. (ISTR this may have been more of an issue with early UMCs.)

 

[David99]

The owners manual states that best practice is to plug the car in whenever you are not driving it, if possible.
A connected Tesla is a happy Tesla.

It is a well known fact that higher state of charge causes more degradation. It's not like up to 90 is fine and anything above is bad. The lower the better. Tests have shown that the difference on degradation between 20% and 30% is small, the difference between 80% and 90% is bigger. If you keep your car plugged in and charging to 90% all the time, your average state of charge is close to 90%. If you charge to 90 every night but just drive during the day, your average state of charge is much lower and your battery will have less degradation. That's a fact, not a theory.

Now the reason why Tesla recommends to always plug in is so people make it a habit and don't forget. They always have a car with plenty of range. The #1 argument against EV is limited range, so Tesla wants to make sure owners keep their range up. They also want to fight the old gas habit that you only worry about filling up once a week when it gets close to zero. The recommendation to plug in all the time has nothing to do with keeping the battery healthier.

In almost 3 years of owning my Model S I had a few emergencies where I need the car quick. Trips to the ER, picking up someone, running an errand for work last minute. None of those required me to drive 200 miles, though. They were all within 30 miles or so. So the state of charge was really irrelevant.

 

[Rocky_H]

The #1 argument against EV is limited range, so Tesla wants to make sure owners keep their range up.

Absolutely this.

 

[mal_tsla]

Can you cite the source/tests stating that degradation is worse at 90% than 80%? Tesla doesn't ever mention this in any of their literature. I would like to study it.

Not to be overly argumentative, but Here's what Tesla literature does say (emphasis theirs) on page 134:

Quoting:
"The most important way to preserve the Battery is to LEAVE YOUR Model X PLUGGED IN when you are not using it.
...
There is no advantage to waiting until the Battery's level is low before charging. In fact, the Battery performs best when charged regularly."

We can perhaps agree to disagree, but to me that phrasing and use of all caps for emphasis reads like Tesla trying to dispel myths, not Tesla trying to trick me into not having range anxiety for the sake of driving EV acceptance.

Those quotes, combined with the absence of any warnings against charging to 90% anywhere in the manual and hobbyist experience with lithium ion batteries in the past forms the basis of my opinion on this.

I trust Tesla to establish 90-100 as the margin of battery performance necessary to ensure acceptable battery longevity.

It is a well known fact that higher state of charge causes more degradation. It's not like up to 90 is fine and anything above is bad. The lower the better. Tests have shown that the difference on degradation between 20% and 30% is small, the difference between 80% and 90% is bigger. If you keep your car plugged in and charging to 90% all the time, your average state of charge is close to 90%. If you charge to 90 every night but just drive during the day, your average state of charge is much lower and your battery will have less degradation. That's a fact, not a theory.

Now the reason why Tesla recommends to always plug in is so people make it a habit and don't forget. They always have a car with plenty of range. The #1 argument against EV is limited range, so Tesla wants to make sure owners keep their range up. They also want to fight the old gas habit that you only worry about filling up once a week when it gets close to zero. The recommendation to plug in all the time has nothing to do with keeping the battery healthier.

In almost 3 years of owning my Model S I had a few emergencies where I need the car quick. Trips to the ER, picking up someone, running an errand for work last minute. None of those required me to drive 200 miles, though. They were all within 30 miles or so. So the state of charge was really irrelevant.

 

[mal_tsla]

Well yes, which is why I was suggesting people evaluate their own situations rather than the emphatic "always do this" type of blanket recommendations you were giving.

Fair enough, but I see far more "always do this" advice on the other end of the spectrum. I almost bought into it myself pre-ownership.

 

[Canuck]

Can you cite the source/tests stating that degradation is worse at 90% than 80%? Tesla doesn't ever mention this in any of their literature. I would like to study it.

The reason Tesla does not mention it is because of what the EPA did to Nissan when they offered the "Long life" mode.

If Tesla thought 90 was just as good as 80 then you wouldn't have the slider which places 90 at the very top end. I doubt 80 to 90 is that big of a difference but Tesla wants you even lower hence the slider -- they won't say that because of the EPA potential hit on range -- but science tells us that cycling a lithium ion battery around 50 gives it the longest life...

Lower charge voltages prolong battery life and electric vehicles and satellites take advantage of this. Similar provisions could also be made for consumer devices, but these are seldom offered; planned obsolescence takes care of this.

Lithium-ion suffers from stress when exposed to heat, so does keeping a cell at a high charge voltage.

Tesla has tackled the heat (unlike Nissan). It's up to you to tackle the charge voltage. That is, if you want to prolong battery life. Degradation is not covered by the warranty.

 

[mal_tsla]

I think it's time to retire from this thread, now that we are speculating about Tesla withholding important battery maintenance guidelines for political reasons.

Risking falling into technical discussion without adequate information about exactly how Tesla manages their batteries :

Most of the information in the articles you link is congruent with my thoughts. It's a very complex topic and basically I advocate for trusting Tesla to manage the battery properly within their own recommended usage guidelines.

Keeping the car charged frequently effectively reduces depth of discharge, which is a primary way to preserve batteries. To discuss the effects of charging to 90% vs 60% we need to know the voltage (at minimum) that correlates to those charging positions on the slider.

I propose that only positions above 90% will charge the cells to the upper "dangerous" volt ranges and that's why warnings show up on-screen when you do so. Do you know otherwise?

 

[mal_tsla]

I think we can learn from each other. Maybe we should start a new thread to discuss further?

 

[Saghost]

Keeping the car charged frequently effectively reduces depth of discharge, which is a primary way to preserve batteries. To discuss the effects of charging to 90% vs 60% we need to know the voltage (at minimum) that correlates to those charging positions on the slider.

I propose that only positions above 90% will charge the cells to the upper "dangerous" volt ranges and that's why warnings show up on-screen when you do so. Do you know otherwise?

There's some data on the TM-Spy thread about cell voltages at states of charge, and you could probably get more detailed data by requesting it there from one of the folks with TM Spy hardware installed...

Using TM-Spy to see Model S data.

It looks like 90% is around 4.08V per cell:

Using TM-Spy to see Model S data.

58.5% was around 3.795V

Using TM-Spy to see Model S data.

This post shows 76% and around 3.94V:

Using TM-Spy to see Model S data.

 

[mal_tsla]

If 90% is 4.08v and assuming their cells are 4.2v rated or higher, it sounds like Tesla put the daily change limit right about where it belongs.

This also assumes the same pack design across vehicles, since their slider is setting a % of max range, not a specific voltage level.

 

[mal_tsla]

All this talk about batteries reminded me to run a storage charge cycle on my toy car's batteries!

 

[Canuck]

I think it's time to retire from this thread, now that we are speculating about Tesla withholding important battery maintenance guidelines for political reasons.

Right, because nothing is ever done for political reasons.

You look to be a relatively new Tesla owner, right? So you have no idea about the previous Tesla warnings, correct? Because they are very different from today and everything changed at the same time as the EPA and Nissan issue. I was following it live, owning both a Leaf and a Tesla for years. Also, do you know who wk057 is? He's probably the number one expert on Teslas outside of Tesla. He's dissected the batteries, hacked the firmware, and even made a pre-AP car into AP. He said this:

Now it only gives you the warning if you leave the car set at > 90% for several charge sessions. It'll pop up with the warning message letting you know that you shouldn't do this regularly (don't know the exact warning). Probably works out so that the EPA didn't see it. lol.

Range Charge Issue -- Forgetting To Reset Back Down

With respect to you, I'll go with the speculation by wk057 over your comments above. If it walks like a duck, talks like a duck, it's a duck. But you likely haven't been around long enough for the walking and talking part.

I propose that only positions above 90% will charge the cells to the upper "dangerous" volt ranges and that's why warnings show up on-screen when you do so. Do you know otherwise?

You can propose all you want but it's pure rubbish. I've taken a keen interest in EV's and lithium ion batteries and I have watched the experts in the field give lectures on how lithium ion batteries work with all its pros and cons. But even a rudimentary knowledge of how a lithium ion battery works, and how the cathode degrades with the amount of ions proves your "proposal" that only above 90% is "dangerous" is wrong. That's aside from the fact that this has nothing to do with danger. This has to do with keeping the cathode in an optimal state with the least degradation as it performs and ages. Watch the Youtube videos by the experts, understand how these battery operate, look at the studies, and you will learn that it is a fact that cycling around 50% causes the least degradation.

End of Rant.

I'm coming honey...

 

[mal_tsla]

You sound like a smart guy, but you're insisting without evidence that 90% on the slider equates to battery-damaging high voltage.

I think Tesla simply simultaneously improved their battery tech and adjusted the mappings on the charge limit settings so that 90% is considered safe. And presto! no more warnings needed.

I'm not arguing against 50% being the least degradation. I'm arguing charging to 90% doesn't produce enough more degradation to matter in a typical ownership experience (eg 10 years average mileage driving). 50% is surely ideal, but 90% is plenty practical. I don't need this car to last for 300,000 miles.

You may be right, but so may I. No need to get frustrated. See ya around!

Right, because nothing is ever done for political reasons.

You look to be a relatively new Tesla owner right? So you have no idea about the previous Tesla warnings, correct? Because they are very different from today and everything changed at the same time as the EPA and Nissan issue. I was following it live, owning both a Leaf and a Tesla for years. Also, do you know who wk057 is? He's probably the number one expert on Teslas outside of Tesla. He's dissected the batteries, hacked the firmware, and even made a pre-AP car into AP. He said this:



Range Charge Issue -- Forgetting To Reset Back Down

With respect to you, I'll go with the speculation by wk057 over your comments above. If it walks like a duck, talks like a duck, it's a duck. But you likely haven't been around long enough for the walking and talking part.



You can propose all you want but it's pure rubbish. I've taken a keen interest in EV's and lithium ion batteries and I have watched the experts in the field give lectures on how lithium ion batteries work with all its pros and cons. But even a rudimentary knowledge of how a lithium ion battery works, and how the cathode degrades with the amount of ions proves your "proposal" that only above 90% is "dangerous" is wrong. That's aside from the fact that this has nothing to do with danger. This has to do with keeping the cathode in an optimal state with the least degradation as it performs and ages. Watch the Youtube videos by the experts, understand how these battery operate, look at the studies, and you will learn that it is a fact that cycling around 50% causes the least degradation.

End of Rant.

I'm coming honey...

View attachment 204328

 

[Saghost]

I'm not arguing against 50% being the least degradation. I'm arguing charging to 90% doesn't produce enough more degradation to matter in a typical ownership experience (eg 10 years average mileage driving). 50% is surely ideal, but 90% is plenty practical. I don't need this car to last for 300,000 miles.

It seems like very few people drive Teslas for "typical mileage. I know I'm driving mine close to twice as much so far (3 months of data) as my typical past car, and the anecdotes I read on the subject say the same - folks like driving it (or it driving) so much that they drive a lot more with one.

Then again, cars that are abused (200,000 miles in 18 months, charged to 100% and supercharged every day) apparently still hold up incredibly well (6% loss in 200,000 mies.)

 

[Canuck]

You sound like a smart guy, but you're insisting without evidence that 90% on the slider equates to battery-damaging high voltage.

You have the terms wrong. Lithium-ion batteries degrade. That's just a fact. There is no such thing as "battery-damaging high voltage" unless you blow them out, which the BMS won't allow you to do. So get that term out of your mind.

The issue is one of degradation. Your car battery is going to degrade. That's just a fact. But we know from studying the cells that, say you use 20% on average, the degradation is less if you go from 60 to 40 daily than from 90 to 70 daily. That is a fact. It's based on the science of how these batteries work, but it's also been replicated by taking a single 18650 cell, doing this test repeatedly, then analyzing the cathode's degredation. Guess which one degraded more?

The issue becomes how much is too much when sacrificing range -- daily driving range vs. long term battery range? That's why we have the slider. 90% is probably okay, especially because most people don't keep these vehicles for many years and Tesla has managed the heat, which really helps with high states of charge. So I don't want to cause you concern about charging to 90%. if that works for you, fine. Just understand it's not the same when it comes to degradation as lower states of charge, despite how much we would like that to be.

I am really leaving now but thanks for the discussion.

 

[mal_tsla]

That's an oversimplification. I'm sure we could banter about this forever and I would guess that might be enjoyable. For the sake of anyone that reads this later, I'll dip my toe into why I think your last statement is an oversimplification:

For one, it ignores depth of discharge effects on degradation. For example, if your charging habit of 50% leads you down to 15% sometimes day due to unexpected traffic, detour, a few unplanned errands, etc, that is worse for lithium batteries than running it down from 90% to 55%.

Also, high cell voltage is indeed a major factor in degradation. When Tesla puts 90% on a GUI, we can't assume that's a particular voltage. Evidence suggests it is a sufficiently low voltage to cause minimal extra wear.

Under-volting and over-volting lithium cells is very much a safety issue. It's not "dangerous" in a Tesla, sure, but that's only because of the way they safeguard the cells.

Like I said, my thoughts are: its complicated. Trust the smart scientists and engineers at Tesla to handle it properly. Charging frequently to 90% at full amps is probably within their design goals for longevity given typical vehicle lifetimes or else you'd see the warnings.