LFP. Weekly Charging vs Daily Charging

[hgmichna]

My hunch is that it's the opposite - Tesla knows the BMS is being slightly pessimistic (for good reason, as you mention earlier), but that pessimism is essentially a systematic error term that will accumulate over many partial charge/discharge cycles, to the point that it shows an excessively low range estimate. Charging the LFP battery to 100% regularly will reset that accumulated error term in the estimate.

Yes, that's possible. However, an overpessimistic mileage display does not hurt anybody. As long as people charge as many miles as they need, they will get as far and will never run out of charge before zero. Everything will work fine.

The only exception is that the maximum possible mileage also shrinks. This would irritate people who do not understand the background. Insofar you are probably right. Tesla wants to avoid showing an ever-reducing maximum range, so they recommend a weekly full charge. Makes perfect sense.

The remaining interesting fact is that, once you understand this, you don't need to charge to 100%, except before a long drive. You know that the shrinking max range will be corrected whenever you charge to 100%.

Of course there is also the possibility that we are mistaken, that we are overlooking something or don't know enough. I, for one, will take this risk.

 

[Redhill_qik]

I just got my M3 RWD with an LFP battery a few days ago and I have a couple of questions.

First, when I took delivery it was only at 50% and I was charging it on mobile charger on the 120V/12A (1.4kW) when it got to 100% the app said that there was 30 minutes remaining which seemed fine to me, but it was actually another 2 hours before it stopped charging adding another 2.8 kWh. Is that a first time 100% behavior, or something that is expected every time? I was hearing a fan-like noise from the front end. BTW, it was definitely still charging at 1.4kW as I could see the house load stay constant as I also have Tesal Solar+Powerwall in the app until it the charging actually stopped..

I did see the following in the user manual, but another 2.8 kWh and 2 hours is more than a low amount IMHO:

When charging to 100%, the vehicle may continue to charge with low power when charging is displayed as complete. This is expected operation. Because the added energy beyond this point is low, it is usually not beneficial to continue charging.

Second, the M3 user manual says to leave it plugged in, is anyone doing this? Will leaving it plugged in keep it from sleeping and not getting upgrades?

CAUTION
Tesla strongly recommends leaving Model 3 plugged in when not in use. This maintains the Battery at the optimum level of charge.

 

[cafz]

First, when I took delivery it was only at 50% and I was charging it on mobile charger on the 120V/12A (1.4kW) when it got to 100% the app said that there was 30 minutes remaining which seemed fine to me, but it was actually another 2 hours before it stopped charging adding another 2.8 kWh. Is that a first time 100% behavior, or something that is expected every time?

When it keeps charging for a while at 100%, it's balancing the cells in the battery pack. It doesn't always take the same amount of time.

I did see the following in the user manual, but another 2.8 kWh and 2 hours is more than a low amount IMHO:

Not all of that has gone into the battery. Consider that just the computers etc use 400W while the car is awake - that accounts for 0.8kWh on its own. It also sounds like battery heating or cooling was taking some power.

Second, the M3 user manual says to leave it plugged in, is anyone doing this? Will leaving it plugged in keep it from sleeping and not getting upgrades?

Plugging it in does not stop it from sleeping. Sentry mode does, though.

 

[hgmichna]

I've been testing my Model 3 with 60 kWh LFP battery for several months now. I charge to exactly 70%, except before a longer drive. If I know I'll have to charge while travelling, I always charge to 100% and usually keep the battery at 100% for a couple of hours before setting out.

At 70% my car used to show an EPA range of 304 km = 189 miles. Now, after more than a month without any full charging, at 70% it shows 300 km = 186 miles. This slight reduction could be a mixture of slight degradation and a pessimistic Battery Management System (BMS). I will see what it shows after my next long trip.

But what I can already see is that there is no serious problem. With these numbers it is unlikely that the battery will run empty before showing 0%. So my recommendation is to use this charging strategy and check whether the displayed range at your favorite percentage rises from week to week or from month to month. If it does, you should charge to 100% to recalibrate the BMS. I guess though that the displayed range will never rise, so you can stick to this charging strategy and rely on the BMS to keep you on the safe side, by being pessimistic.

It won't hurt to charge to 100% once every one, two, or three months to recalibrate the BMS and to check whether you're still on the safe side.

As has been written before, charging to 70% is a measure to reduce the battery's calendar degradation. It won't make a huge difference, but if you plan to drive your car for longer than 10 years, it may still be worth the little trouble. Measurably less degradation may translate into a higher price for the used car.

 

[Vostok]

It won't hurt to charge to 100% once every one, two, or three months to recalibrate the BMS and to check whether you're still on the safe side.

I have the NCA chemistry in my Long Range Model 3, and with normal city driving (not very long distances a few times per week) the maximum range in km reported by the Tesla App when moving the charging slider all the way to 100%* slowly declined over time. Note I would not actually charge to 100%, I would just see what the App thought the range would be if I did, then move the slider back to 80% typically.

When I bought the car the range fully charged was reported as 499 km. After 2 and a bit years, sometimes it would be as low as 465 km. But I’ve found that after doing long road trips and the occasional charge to 100% the reported range at full charge would go higher. On my most recent road trip, when I charged to 100% once near the end of the trip, the range was reported as 480 km.

After a week back and normal driving routine, when I once charged to 90%, the range was reported as 450 km. Which when extrapolated implies 500 km at 100%.

So it seems the BMS does need the car to do the occasional “leg stretch” trip along with 100% charges to recalibrate.

* Note: recent updates to the App no longer shows this any more - just charge percentage - even if you’ve set the battery indicator in the GUI to show km.

 

[maxkonji]

Very interesting read, thanks for sharing
I recently changed charging behaviour and charging almost daily (last 2 weeks) to take advantage of newly installed solar panels
I noticed the 100% range dropped from 415 to 412. May change back to how I was charging before (twice weekly)

Appreciate not wanting a lengthy discussion

My thoughts are based on

How I Recovered Half of my Battery's Lost Capacity

Like many others, I have been concerned with loss of 100% indicated battery range on one of my Model 3s. My P3D (build date 9/13/2018, delivery date 10/8/2018) had gotten down to 270.3 miles at 100% charge on January 20, 2020, at about 30,700 miles, which is a loss of 40.8 miles since the car...

teslamotorsclub.com

And

Tesla battery management system (BMS) calibration

Tesla battery management system (BMS) calibration instructions

tesla-info.com

If you Google the topic on here you’ll also find more people saying they’ve done essentially these things and got back range.

I guess the only other thing I’d add is it kind of makes sense to me that a range of voltage readings across the spectrum might help but I don’t know why really. The energy used between the different voltages might also be useful.

At the risk of having that lengthy debate what makes you doubt it?

 

[hgmichna]

So it seems the BMS does need the car to do the occasional “leg stretch” trip along with 100% charges to recalibrate.

More so with the LFP battery, which is the topic of this thread. You also confirm that the BMS stays on the safe, pessimistic side when not well-calibrated.

Charging to 100% before a long-distance drive seems to be a good idea.

 

[karlos22]

I’m sceptical about higher rates of degradation with calendar ageing if you are charging to higher SOC with the LFP. The voltage curve is almost completely flat between 10-95%, which suggests to me that anywhere between those values will make very little difference. This isn’t an NCA where the voltage difference between 40% and 90% is significant.

Unfortunately it will takes years to get any decent data on this. Ultimately with a lifespan of 3000+ cycles, it isn’t worth worrying about. An extra 1-2% battery capacity doesn’t mean anything come sale time, especially since you can’t even directly read the battery health in any sort of meaningful way. It’s all a guessing game. Can you accurately tell me what your battery health is right now?

Just follow what the manual says and don’t worry about it.

 

[ausevdriver]

I noticed the recent update of the app (iOS) is even more clear, and made the advice from the user manual front and center.

If you have the charge slider at less than 100% it now says "For battery health set the charging limit to 100% and charge to 100% at least once a week.".

And it's a good thing, it's how EVs need to be if they are going to be mainstream. Nobody wants to be worrying about this sort of stuff. If they really had a concern about cars being left at 100% they would program in things like "stop charging and burn off some power if sat at 100% for >24 hours"

 

[BreatheSafe]

As has been written before, charging to 70% is a measure to reduce the battery's calendar degradation. It won't make a huge difference, but if you plan to drive your car for longer than 10 years, it may still be worth the little trouble. Measurably less degradation may translate into a higher price for the used car.

Sorry this doesn't make sense to me. Calendar degradation is just that, over time it occurs and there is really nothing that can be done about it.
Once a battery is produced and put into service it starts the degradation process. How the battery is treated adds to the degradation.
You can choose to treat your battery as you see fit but I would rather choose the manufacturers recommendation which comes from a much larger data set.
If LFP is as stable as suggested and with lower levels of degrading when comparing to current battery tech then worrying about how much, when to charge and formulating new theories is counter intuitive for the masses.
Plug it in - drive - plug it in.

 

[karlos22]

Sorry this doesn't make sense to me. Calendar degradation is just that, over time it occurs and there is really nothing that can be done about it.
Once a battery is produced and put into service it starts the degradation process. How the battery is treated adds to the degradation.
You can choose to treat your battery as you see fit but I would rather choose the manufacturers recommendation which comes from a much larger data set.
If LFP is as stable as suggested and with lower levels of degrading when comparing to current battery tech then worrying about how much, when to charge and formulating new theories is counter intuitive for the masses.
Plug it in - drive - plug it in.

What he/she is saying has some merit, you can google it for yourself “LFP calendar degradation “ as there are lab tests conducted. From what I saw, at SOC 50% the degradation will be lowest. Of course this is talking about STORAGE for 400+ days and does not reflect real world use. Also, temperature is far more detrimental to degradation than SOC, which you do not need to worry about with your tesla.

TLDR; if you aren’t going to drive the car for months then charging to 50% is a good idea. For normal use, setting lower charge limits than 100% once a week and the benefits that produces is debatable and yet to be seen. Just enjoy the car!

 

[Maximillan]

tl;dr Teslas don't degrade very much

 

[Stratman]

I’m sceptical about higher rates of degradation with calendar ageing if you are charging to higher SOC with the LFP. The voltage curve is almost completely flat between 10-95%, which suggests to me that anywhere between those values will make very little difference. This isn’t an NCA where the voltage difference between 40% and 90% is significant.

Unfortunately it will takes years to get any decent data on this. Ultimately with a lifespan of 3000+ cycles, it isn’t worth worrying about. An extra 1-2% battery capacity doesn’t mean anything come sale time, especially since you can’t even directly read the battery health in any sort of meaningful way. It’s all a guessing game. Can you accurately tell me what your battery health is right now?

Just follow what the manual says and don’t worry about it.

degradation is not just about voltage. With LFP I would not get too stressed about charging regularly to higher SOC say 90% as the LFP chemistry trade off in reduced capacity compared to NCA, is on the plus side, less long term cell degradation and far more cycle life. The cars will wear out before the LFP battery does.

 

[Vostok]

tl;dr

With a link to a 53-minute video.

Sorry, I just found that amusingly ironic!

 

[meloccom]

Can’t find the source right now but early results from V2G trials are indicating that the regular small drains on the battery are actually improving the battery life cycle.

 

[karlos22]

tl;dr Teslas don't degrade very much

this should be posted in the LFP degradation thread, as many (most) people are basing their numbers on the displayed range at 100%. This is probably completely wrong because any real degradation would be hidden by buffers or any error with the BMS.

As bjorn said, it’s just too difficult to accurately measure. Which begs the question, if it’s so hard to measure, does it actually matter?

 

[hgmichna]

I’m sceptical about higher rates of degradation with calendar ageing if you are charging to higher SOC with the LFP. The voltage curve is almost completely flat between 10-95%, which suggests to me that anywhere between those values will make very little difference. This isn’t an NCA where the voltage difference between 40% and 90% is significant.

Unfortunately it will takes years to get any decent data on this. …

The voltage curve has nothing to do with calendar degradation. Also it will not take years to get data. We have it already, quoted here in the forum. LFP batteries are well-researched and well-known.

Calendar degradation is near zero at 0% SoC and maximal at 100% SoC. It is nearly flat between 40% and 70% SoC, which suggests to charge the battery to 70% if you want to prolong its life while still having a reasonable charge for unforeseen driving.

The prolongation is not great, but it could make your battery live 30% longer than if it were kept at 100%.

 

[maxkonji]

That’s a long 53min
I like listening to him but not that much..

With a link to a 53-minute video.

Sorry, I just found that amusingly ironic!

 

[karlos22]

The voltage curve has nothing to do with calendar degradation. Also it will not take years to get data. We have it already, quoted here in the forum. LFP batteries are well-researched and well-known.

Calendar degradation is near zero at 0% SoC and maximal at 100% SoC. It is nearly flat between 40% and 70% SoC, which suggests to charge the battery to 70% if you want to prolong its life while still having a reasonable charge for unforeseen driving.

The prolongation is not great, but it could make your battery live 30% longer than if it were kept at 100%.

Calendar degradation varies with SOC but more so with temperature - something you don't have to worry about with your LFP battery as the car takes care of that for you. In the tests I have seen (which I assume you are referring to), the degradation difference between a storage SOC of 50% and 90% was 0.5% over 400 days at 25c. Since one could argue that most calendar degradation happens in the first few years, this difference is so minimal that I would argue it isn't even worth the effort to worry about - over 10 years we are talking maybe 2%. Also, we are talking about storage here and not real world use, so again the results will vary and this is why I do not agree with you that the data is available; at best it is a partially available. It will take years before we see the real world difference between someone who charged to 100% daily and someone who charged to 50%. It becomes even more complicated than that because I live in a cold climate and you may live in a hot climate, which will skew the results even more. Throw in variations in charging habits etc and it will become almost impossible to know for sure.

It is just too complicated to worry about IMO. If Tesla had any data that suggested charging to between 40-70% will extend your battery life by 30%, they would recommend that. I don't blindly trust Tesla, but considering even the early Model S batteries have aged very well (these are early gen NCA batteries), then I believe that the LFP batteries will surely outlast the car even if you charge to 100% daily.

 

[Vostok]

Just wondering what people who don’t have off-street parking and have LFP batteries do. Do they charge to 100% on public chargers?

That could be a problem if LFP shows the same rapid drop in charge rate near 100% that NCA and NMC chemistries have. These owners are being told to always charge to 100% but that would cripple turnover at a public charger .