Confusion on keeping the charge limit at 100% and charge fully once per week

[sgreadly]

Hi all,

I need some advice on the wording in the Tesla app (not on how to charge as this has been answered in other threads).

I've got a 2021 Model 3, Standard Range Plus, which has an LFP battery based on Control > Software > Additional Info. My charging limit bar is a 0 - 100 where you can change it to whatever limit you need. I set it to 80%. If it helps, I travel ~200km/day, consuming half my battery capacity, it dropps from 80% to 20% daily.

I was told to never charge it to 100% unless I'm doing long distance travels where I'd need the whole battery. Instead, to charge it to 80%, which I've done, and I understand the reasoning. All good there.

The confusion..

Few months back, the Tesla app says to maintain battery health, keep the charge limit at 100% and charge fully once per week.

The wording is confusing to me..

"To maintain battery health, keep the charge limit at 100% and charge fully once per week".

Here's another example too,

This doesn't make sense, as it contradicts itself.

• If I keep the limit at 100% it'll charge to 100% every time.
• Otherwise, to do what the app wants me to, I'd have to manually set it to 80% 6 days a week, and manually to 100% the 7th day, which again contradicts what the app is asking me to do (i.e., keep the charge limit at 100%).

In other words, it's impossible to keep the charge limit at 100% and charge fully once per week. It's either/or, not both.

Is it just me? Or is what they're trying to say worded incorrectly? Or did I misunderstand it?

 

[jjrandorin]

Hi all,

I need some advice on the wording in the Tesla app (not on how to charge as this has been answered in other threads).

I've got a 2021 Model 3, Standard Range Plus, which has an LFP battery based on Control > Software > Additional Info. My charging limit bar is a 0 - 100 where you can change it to whatever limit you need. I set it to 80%. If it helps, I travel ~200km/day, consuming half my battery capacity, it dropps from 80% to 20% daily.

I was told to never charge it to 100% unless I'm doing long distance travels where I'd need the whole battery. Instead, to charge it to 80%, which I've done, and I understand the reasoning. All good there.

The confusion..

Few months back, the Tesla app says to maintain battery health, keep the charge limit at 100% and charge fully once per week.

The wording is confusing to me..



Here's another example too,

This doesn't make sense, as it contradicts itself.

• If I keep the limit at 100% it'll charge to 100% every time.
• Otherwise, to do what the app wants me to, I'd have to manually set it to 80% 6 days a week, and manually to 100% the 7th day, which again contradicts what the app is asking me to do (i.e., keep the charge limit at 100%).

In other words, it's impossible to keep the charge limit at 100% and charge fully once per week. It's either/or, not both.

Is it just me? Or is what they're trying to say worded incorrectly? Or did I misunderstand it?

Some people may not be able to fully charge the vehicle every time they plug it in, thus, on a LFP battery equipped Model 3, Tesla is advising you that you should both keep the charge limit at 100% and also fully charge it to 100% at least once per week.

Where it appears you are getting confused is the "I was told to never charge it to 100%" statement, as that is not applicable to the LFP batteries. The other thing it appears that you are forgetting is what I said above, that not everyone can charge to 100% for many reasons, even if they have it set that way (dont have home charging, charging on a slow connection, etc etc.

 

[sgreadly]

Some people may not be able to fully charge the vehicle every time they plug it in, thus, on a LFP battery equipped Model 3, Tesla is advising you that you should both keep the charge limit at 100% and also fully charge it to 100% at least once per week.

Where it appears you are getting confused is the "I was told to never charge it to 100%" statement, as that is not applicable to the LFP batteries. The other thing it appears that you are forgetting is what I said above, that not everyone can charge to 100% for many reasons, even if they have it set that way (dont have home charging, charging on a slow connection, etc etc.

Thanks!

So setting it to 100% and charging fully is for those that may not be able to fully charge all the time. But for us that have a charger at home, then we should just keep doing what we do, which is to set the limit to 80% except once a week, to 100%.

Does that sound about right ?

Ta.

 

[jjrandorin]

I cant give you any recommendations for charging a LFP tesla model 3. What you are saying sounds fine, but if you want more feedback, I recommend you connect with people who are discussing that battery in depth, etc, in the 42+ page thread we have on that topic, here:

Model 3 SR+ LFP Battery Range, Degradation, etc Discussion

I was going to drive until 5-10% remaining to do the test. That should allow quicker discharge and after ending the test I would have 100% charged. I wonder how the car would discharge, perhaps by preconditioning the battery pack. Yep, apparently it runs the low efficiency compressor to...

teslamotorsclub.com

"what percentage should I charge to" is the root of pretty much every battery thread (that and "why am I not getting my rated range").

The above thread would be the one I recommend, to discuss charging percentages etc.

 

[sgreadly]

Cheers,

I'll read through that soon.

 

[Tam]

Cheers,

I'll read through that soon.

You might think about the traditional Lithium battery since 2008 Roadster to current non-standard range Tesla. These cars need to avoid 100% unless there is a good reason like a road trip.

Now you have standard range with LFP, so 100% is Tesla's preferred way. If you can't do it all the time, then at least once a week.

The instruction is very clear to me.

In your case, instead of habitually setting to 80%, change it to 100%.

From the manual:

"Lithium Iron Phosphate Batteries​

Some vehicles are equipped with a Lithium Iron Phosphate (LFP) Battery. To determine if your vehicle has an LFP Battery, navigate to Controls > Software > Additional Vehicle Information.
If your vehicle is equipped with an LFP Battery, Tesla recommends that you keep your charge limit set to 100%, even for daily use, and that you also fully charge to 100% at least once per week. If Model 3 has been parked for longer than a week, Tesla recommends driving as you normally would and charge to 100% at your earliest convenience."

There is no contradiction. There's no confusion. However, whether you agree with that instruction is another issue.

 

[sgreadly]

Now you have standard range with LFP, so 100% is Tesla's preferred way. If you can't do it all the time, then at least once a week.

Honestly, with me it's the lack of experience on this.

If 100% every day is the preferred way and ok to do, I can do it, no worries.

Otherwise, if 80% 6 days and 100% 7th is required or beneficial, again I can do it, no worries.

All I care is to do the right thing to maximise the battery's health, and reduce degradation as much as possible, as I intend to keep the car for a while (not the kind of guy that sells and upgrades every few years).

 

[3sr+buyer]

LFP batteries have different characteristics from NCA batteries found in most Teslas.

• Probably degrades less and slower.
• BMS may get inaccurate if not charged to 100% for a while.

Degradation may be less if you charge to 70% or lower, but then that risks a surprise if the BMS gets inaccurate while you think you have 10% left on the way home.

If I had your situation, I would charge to 100% on nights before your long daily commute, using scheduled departure to finish charging just before leaving, but charge to 70% or lower for days when substantially less driving is to be done.

This would minimize the time spent at high state of charge (>70%), but also keep the BMS in sync because it will see 100% several times per week.

 

[sgreadly]

LFP batteries have different characteristics from NCA batteries found in most Teslas.

• Probably degrades less and slower.
• BMS may get inaccurate if not charged to 100% for a while.

Degradation may be less if you charge to 70% or lower, but then that risks a surprise if the BMS gets inaccurate while you think you have 10% left on the way home.

If I had your situation, I would charge to 100% on nights before your long daily commute, using scheduled departure to finish charging just before leaving, but charge to 70% or lower for days when substantially less driving is to be done.

This would minimize the time spent at high state of charge (>70%), but also keep the BMS in sync.

Perfect, which is what I exactly do at the moment. But for me it's 80% instead of 70% as I drive ~200km a day, bring it down from 80% to 20%.

I'll stick with that for now, and keep reading along for curiosity sake (and to learn more).

 

[bruce4000]

cleanerwatt had a really good LFP battery YT video on this subject a few days ago. Short story Is that LFP has a lower voltage than Nickel based Lithium ion so not as detrimental to go to 100 % but still shortens the life compared to not sitting at 100%. However, LFP has a very non linear voltage vs charge curve so you need to regularly charge to 100% so bms can better determine state of charge. Nickel based has a more linear curve so can better determine state of charge without going to 100%.
My takeaway is ideally charge to say 80% for your daily commute (usually not worried about running out of battery), and then once a week charge to 100% so can recalibrate.

 

[sgreadly]

cleanerwatt had a really good LFP battery YT video on this subject a few days ago. Short story Is that LFP has a lower voltage than Nickel based Lithium ion so not as detrimental to go to 100 % but still shortens the life compared to not sitting at 100%. However, LFP has a very non linear voltage vs charge curve so you need to regularly charge to 100% so bms can better determine state of charge. Nickel based has a more linear curve so can better determine state of charge without going to 100%.
My takeaway is ideally charge to say 80% for your daily commute (usually not worried about running out of battery), and then once a week charge to 100% so can recalibrate.

Perfect. Thank you I'll keep doing that.

Awesome support from all btw. Very happy with this forum!

 

[3sr+buyer]

Perfect, which is what I exactly do at the moment. But for me it's 80% instead of 70% as I drive ~200km a day, bring it down from 80% to 20%.

I'll stick with that for now, and keep reading along for curiosity sake (and to learn more).

Actually, what I wrote is the opposite.

 

[sgreadly]

Actually, what I wrote is the opposite.

Oh,

My impression of my daily 200km drive is it's considered a 'less driving' type of drive, since it only uses about 50% of the battery. While the long commutes are those that require the whole battery, or multiple cycles like journeys across cities, holiday travel, etc.. (with fast charging within the journeys)

But yes I get the gist of it.

 

[Tam]

...All I care is to do the right thing to maximise the battery's health, and reduce degradation as much as possible, as I intend to keep the car for a while (not the kind of guy that sells and upgrades every few years)...

That is different than not understanding Tesla's instructions.

People do understand Tesla's instructions fine, but they question its wisdom and Tesla owners make their own instruction.

The theory is: the lower State of Charge is better for your battery health.

The chart from BatteryUniversity.com:

"a Li-ion battery cycled within 75%–25% SoC (blue) would fade to 74% capacity after 14,000 cycles. If this battery were charged to 85% with same depth-of-discharge (green), the capacity would drop to 64% at 14,000 cycles, and with a 100% charge with same DoD (black), the capacity would drop to 48%."

But remember, that is not what Tesla wants you to do.

 

[sgreadly]

Interesting! Ok.. I may give 75% a try instead of 80%. And yes I'm still reading through all this

Ta.

 

[3sr+buyer]

My impression of my daily 200km drive is it's considered a 'less driving' type of drive, since it only uses about 50% of the battery.

You mentioned going from 80% to 20% before, which would be using 60% instead of 50%.

If you only use 50% (rather than 60%), then starting at 70% ends the day at 20%, which is probably enough that BMS inaccuracy is unlikely to leave you stranded, if you do charge to 100% once per week.

 

[sgreadly]

You mentioned going from 80% to 20% before, which would be using 60% instead of 50%.

If you only use 50% (rather than 60%), then starting at 70% ends the day at 20%, which is probably enough that BMS inaccuracy is unlikely to leave you stranded, if you do charge to 100% once per week.

Apologies.. busy day and multitasking.

I can't remember any more if it drops to 30% or 20%.. lol. I'll keep an eye out tomorrow. I'm pretty sure it was 50% usage so it might've been down to 30%, though some days I do drive an extra bit so it may drop to 20%.

Thanks for the advice. I'll take it into consideration and adjust my limit accordingly.

 

[SageBrush]

This is an interesting thread. It seems clear that the LFP BMS needs charging to 100% SoC weekly to stay accurate. The unanswered question is how much degradation is added to a pack from daily charging to 100% compared to some lesser value. More than zero, I'l wager

I'm surprised that Tesla has not modified the software to automagically charge weekly to 100%, but otherwise follow the owner's charge limit preference.

 

[Chris55555]

That is different than not understanding Tesla's instructions.

People do understand Tesla's instructions fine, but they question its wisdom and Tesla owners make their own instruction.

The theory is: the lower State of Charge is better for your battery health.

The chart from BatteryUniversity.com:

"a Li-ion battery cycled within 75%–25% SoC (blue) would fade to 74% capacity after 14,000 cycles. If this battery were charged to 85% with same depth-of-discharge (green), the capacity would drop to 64% at 14,000 cycles, and with a 100% charge with same DoD (black), the capacity would drop to 48%."

But remember, that is not what Tesla wants you to do.

2000 cycles on your graph represents about 260,000 miles at 50% of a full LFP pack, which covers most use cases. The data for 4000, 6000 or even extrapolation to 14000 cycles isn't valid for most users, since almost no one puts more than 500,000 miles on a car.

Looking at the 2000 mark, the difference between "good" and "bad" charging is 92% versus 86%. This 6% difference is about 15 miles, which is pretty negligible, even for a small battery.

 

[Olle]

This is an interesting thread. It seems clear that the LFP BMS needs charging to 100% SoC weekly to stay accurate. The unanswered question is how much degradation is added to a pack from daily charging to 100% compared to some lesser value. More than zero, I'l wager

Since LFP can tolerate 100% SOC relatively well, you don't necessarily need the costly hardware that moves energy between cells at lower SOC. Instead, you can use bleed resistors that activate as soon as its cell reaches Vmax. Once all cells reach 100% SOC the charge session stops and no more energy is bled off/lost. Simple! (Side note: This is how many NMC and NCA packs worked in the old days and the reason for the unfortunate advice/rumor to charge other Teslas to 100% once a month helps with balancing. Terrible idea btw.)

If a Vmax balanced LFP pack would not get a chance to reach 100% often enough, it would drift out of balance and not only lose capacity for the session but also lose physical cell capacity at an accelerating pace as the weaker cells increasingly hit their max/min, they degrade more than the others, which in turn puts the pack out of balance quicker for each session, which in turn degrades weak cells quicker yet. To make matters worse in a bleed resistor pack, the weak cells receive heat from their respective resistors, which happens early if out of balance. Heat combined with high SOC accelerates degradation.

This is why I would guess that overall degradation is less if charged to 100%, for this particular pack.