Should LFP batteries be charged to 100%?

[Steely]

As the website clearly says that none of this needs to be followed, I talked to Tesla via the chat...

 

[mpandrew]

After spending 57k on the car plus another 3k in PPF - I would love to be keeping this car for a good 10 years+

Its going to take 6 before I start really "saving" money as then my running costs are basically 0 after the finance is paid off.

BUT, if in 6-8 years time, my car was still worth a decent chunk and I could upgrade for a relatively small extension to the finance...sure i'd be tempted.

I just worry about keeping the car to a point where its lost so much value (mainly due to battery degradation) that I end up stuck with a worthless dud and have to start this process all over again when I eventually upgrade.

Isn't this the problem with car ownership regardless of how it's powered? If you do keep it for 10 years, then £6k/year doesn't seem too crazy a cost to have incurred for that duration of service? I fear that well before your 6 years to get to zero running costs the government will have found a new way to offset any chance of that! Who knows maybe we will all be hailing cars in 10 years and not owning them, or our dear elected leaders will have failed to listen to science and we'll be in some version of Mad Max/Planet of the Apes and car ownership won't be high on your list of priorities?

 

[Billbrown1982]

As the website clearly says that none of this needs to be followed, I talked to Tesla via the chat...

View attachment 657020
View attachment 657021

and yet my car actually came up with a warning message the other day about repeatedly charging to 100% having an adverse affect on the batteries...

Honestly wonder if we will ever know for sure what the right approach is.

 

[Billbrown1982]

Isn't this the problem with car ownership regardless of how it's powered? If you do keep it for 10 years, then £6k/year doesn't seem too crazy a cost to have incurred for that duration of service? I fear that well before your 6 years to get to zero running costs the government will have found a new way to offset any chance of that! Who knows maybe we will all be hailing cars in 10 years and not owning them, or our dear elected leaders will have failed to listen to science and we'll be in some version of Mad Max/Planet of the Apes and car ownership won't be high on your list of priorities?

Yes absoloutely true, although most people know that, a well made diesel engine that has been serviced regularly can go well over 100,000 miles without too much concern.

Not many people know how long batteries will last and infact, most people seem to think they are next to useless within a couple years - so I just worry that it will affect Tesla' resale moreso than a regular ICE car.


Your dead right about zero running costs not lasting though. Congestion charge exemption ends in 2025 for electric cars and I am fully expecting to be paying road tax long before then as well.

Plus i'm still not convinced they won't find some way to charge us an "electric tax" of some sort.

 

[ChunkyRhino]

Yes absoloutely true, although most people know that, a well made diesel engine that has been serviced regularly can go well over 100,000 miles without too much concern.

Not many people know how long batteries will last and infact, most people seem to think they are next to useless within a couple years - so I just worry that it will affect Tesla' resale moreso than a regular ICE car.


Your dead right about zero running costs not lasting though. Congestion charge exemption ends in 2025 for electric cars and I am fully expecting to be paying road tax long before then as well.

Plus i'm still not convinced they won't find some way to charge us an "electric tax" of some sort.

I'm in Victoria Australia. Current conversation in our state Parliament is about implementing as per km tax of 2.5 cents to be charged.

If passed we will have to take a photo of our odometer each time we renew our yearly registration.

This is a tax exclusively for Ev and hybrid cars, not ICE vehicles.

ALSO, to the OP - amazing post thankyou, I take delivery of the SR+ soon. I'm glad I came across this thread

 

[Adopado]

I'm in Victoria Australia. Current conversation in our state Parliament is about implementing as per km tax of 2.5 cents to be charged.

If passed we will have to take a photo of our odometer each time we renew our yearly registration.

This is a tax exclusively for Ev and hybrid cars, not ICE vehicles.

ALSO, to the OP - amazing post thankyou, I take delivery of the SR+ soon. I'm glad I came across this thread

That really is surprising! Other than the cheaper "fuel" of an EV do you get any other benefits? e.g. in the UK ICE cars that produce a relatively high carbon output pay an annual car tax but EVs and some low emissions vehicles don't pay anything. I can understand if the government are missing out on tax they would otherwise get on motor fuels but it would seem more sensible to come up with a system that treats all vehicles using a similar principle. The last thing to do is to discourage the uptake of low (or no) emissions vehicles.

 

[Mattallica]

After spending 57k on the car plus another 3k in PPF - I would love to be keeping this car for a good 10 years+

Its going to take 6 before I start really "saving" money as then my running costs are basically 0 after the finance is paid off.

BUT, if in 6-8 years time, my car was still worth a decent chunk and I could upgrade for a relatively small extension to the finance...sure i'd be tempted.

I just worry about keeping the car to a point where its lost so much value (mainly due to battery degradation) that I end up stuck with a worthless dud and have to start this process all over again when I eventually upgrade.

Just remember an ICE car faces a similar struggle if the engine dies outside of warranty. Same fix applies... new batteries/donor batteries.

It is largely a non-issue (albeit costly).

 

[Dommmm]

I work in the battery world but other opinions will exist! I'll dump thoughts in simple terms to try and make it readily understandable. Hope it helps.

LFP, lithium ferro-phosphate is a different cell chemistry, common in China and often used with high power low range applications (buses/trucks). LFP is different to li-ion but neither worse nor better. It charges/discharges very easily, has an exceptional cycle life (you can charge/discharge many times with very little degradation) but at a cost of being less energy dense, so you need more volume to fit the same capacity of battery. You can very roughly equate cycle life to total lifetime mileage of the car - more cycles is more miles before pack needs replacing.

This makes sense for SR+ model, it has space for a very large li-ion battery so using less energy dense LFP Tesla can still achieve the required energy capacity that the SR+ model spec requires. i.e. SR+ with LFP has a bigger battery volume than SR+ with Li-ion.

Interestingly because LFP can discharge so rapidly, Tesla could probably make this model faster without undue harm to the battery. I expect they don't do this purely to keep model performance differences as a marketing ploy, not that the SR+ is slow anyway.

The car probably has an internal buffer, i.e. unused capacity at both ends of the voltage range of the cell. So when you charge to 100% it is likely actually less than this in reality. Same on discharge, when it states 0% they'll be a little left - evidenced by Carwow driving for miles after hitting 0% in their tests. High buffer helps protect the battery in early days and then can be used as the battery does degrade to maintain the stated range. So as capacity diminishes, move towards filling the battery to the real 100% capacity. On the 0% end of the capacity, by leaving some spare energy in reserve, you avoid the car damaging the cells as it continues to discharge to varying degrees when not in use. I expect at some point the car will completely turn off to protect the battery which will need some additional measures to open the charge flap and reenable charging (guessing). LFP models will likely 'supercharge' more easily than the Li-ion cars, certainly at a cell level they absorb energy far more readily but the car software will control it. There is a relationship here though with capacity, a larger battery (LR/Perf) can charge faster than SR+ simply because it has a bigger bucket to fill, so even though the SR+LFP has faster charging capability, because it is a smaller bucket it may actually charge at a similar or slower rate to the bigger siblings. It should however charge faster than the SR+Li-ion.

80% is often cited as an optimal charge level. This is a compromise but a good one - the less energy you store in the battery the more relaxed it is and the less damage caused. Think of the cell like a balloon filled with water, you can fill it to absolutely full but it'll be very stretched and tight and will become weaker - best analogy I can think of! If you can get away with only 50% in the battery and comfortably do all your journeys, then do that and recharge to 50% each day, it will benefit the pack. 80% means you get decent range and helps not stress the battery. 100% is for the days you are doing a long journey and want decent buffer to reach the next charging stop - I've charged my M3LR to 100% twice times in 18 months and even then it wasn't really necessary.

Another aspect of 80% is this is about the point that the pack reaches full charge voltage and switches from a constant current to constant voltage phase. Details are easy to find on the net but in simple terms, charging slows down from about 80% capacity, you'll see this if you watch it at a supercharger. This is why if you can charge to 80% or less and have enough range to get to the next supercharger, that will probably be quicker than charging to 100% and putting less charge in at the next charger or destination when you don't care anyway. As chargers get busier you could hypothesise that Tesla may start nudging up the kWh price after 80% charged to encourage drivers to move off to free up pumps. Note at home on a regularly 7kW charger you won't see this slowing of charge as the rate is already very slow compared to what the battery is capable of accepting.

Charging to 100% for LFP makes some sense, as said they have impressive cycle life even with full charge and discharge, so it will degrade the cell but by an appreciably smaller margin than for the Li-ion pack. By way of example, li-ion based cells get somewhere around 500 cycles before they are judged end of life (which in battery world is actually only 80% of original capacity). LFP will often achieve 2000 - 5000 cycles. Hence why Tesla isn't bothered about you charging to 100% to maximise range as you'll still get more cycle life. You can do the sums but even with 500 cycles of ~200 miles range, that's a 100,000 mile battery that's only lost 20% of capacity -ish. With the SR+LFP model, you're probably going past 500,000 miles before that happens.

The remaining range of the car is a very challenging prediction that the car computer makes and will constantly update. For most lithium based rechargeable systems an occasional 100% charge helps calibrate the algorithm that determines capacity remaining (and thereby range). Otherwise the car is trying to track capacity without a good known starting point. That means it is constantly trying to monitor exact energy consumption at all times (including when not in use) and estimate what is left. Add in that it has to predict temperature as this has an effect of the battery and car efficiency, as well as the parasitic drains on the battery e.g. if it is very cold tomorrow, it won't go as far as it is currently predicting today. ICE cars are no different, they use more fuel for the same journey if it's colder, or if the driver simply chooses to travel more quickly. I suspect that people never gave much thought to the predicted range remaining on their old diesels as it made no difference if you just needed to refill a little earlier given how fuel is so readily available. Remember in the end the range is only a guess and it has no real reflection on the actual true capacity of the battery. I would argue that charging to full and draining to nearly empty to 'calibrate' the range is futile and only helps the human feel better, it doesn't make any difference to the battery itself.

So called phantom drain is a thing, the car uses energy when it's sat doing nothing. Especially if it *is* doing something like cabin pre-heating or Sentry Mode or downloading an update and so on. This is a bit different to your old ICE dinosaur which did tend to do truly nothing when turned off, but then it didn't get regular updates, watch for intruders, defrost the screen while you were eating your cornflakes and so on. Also remember that whilst you have 'paid for' the lost miles, by comparison you've paid a lot less for the actual miles you have journeyed compared to an ICE car so let it slide!

As many others have mentioned, once you're past range anxiety and switch to percentage remaining rather than miles, you'll quickly get used to charging when you need to and relying on superchargers for longer journeys. My own way of using my car is to charge to about 85% once a week timed to finish by the time I'm about to do a commute. This journey gets the car below 80% and I carry on through the weekly commutes. I can usually get a full week of work and back plus a bit of pottering at the weekend from a single weekly charge, particularly as it gets warmer. I tend to not let the car dip below 20% purely because of the reduction on the GO pedal but there isn't any reason not to go lower. You can charge more frequently without any detrimental affect, I just avoid it because it's not necessary and is one less thing to do. With what I now know, I could have leased an SR+ and it would have been absolutely perfect and not affected me very much at all - a few more charges on the long journeys but nothing that I couldn't have managed. Trouble is, now I've had the LR and got used to the performance of it, tough to go back to anything slower next time.

Great explanation and very helpful, appreciate it thanks

 

[SmartElectric]

BUT, if in 6-8 years time, my car was still worth a decent chunk and I could upgrade for a relatively small extension to the finance...sure i'd be tempted.
I just worry about keeping the car to a point where its lost so much value (mainly due to battery degradation) that I end up stuck with a worthless dud

I wonder how many here plan to keep their cars beyond the battery warranty (8 years). I don't so, for me, degradation is a moot point. Buying second hand ev's however should always be done carefully........... caveat emptor.

Our 8.5 year old Model S 85 still charges to 95% original range, and supercharges same rate as new. While I am likely trading it for a Cybertruck in year 10 (2023), I would keep this car forever if Tesla hadn't revealed that stainless steel dent proof monstrosity, darn Tesla!!
All this to say, don't be overly concerned about degradation, our Model S is routinely charged to 100%, driven hard, and in no way "babied".

 

[Peter 224]

O/Poster...Really clear explanation: thank you very much indeed...
And thanks to everyone for adding to the discussion.

Conclusion: For my M3 LR AWD the 80/20 rule applies mostly, but 100 is OK when needed. I have 7kw home charging for the gentle touch...

 

[Scottish mod3]

interesting chat.. I've opted for the MIC SR+ with the LFP battery main reason being the longevity.

Recognising uncertainty around winter weather performance and living with it without access to home charger or relying on supercharger and public charger.

These are risks I'm willing to take as I believe Tesla is light years ahead in BMS compared to other ICE car manufacturers that are just transitioning into EV. I believe the model S has proven that the battery will last for a very long time..

Found interesting video linked below , apparently the LFP battery is rated a million mile? ( in theory).

 

[hpartsch]

I work in the battery world but other opinions will exist! I'll dump thoughts in simple terms to try and make it readily understandable. Hope it helps.

LFP, lithium ferro-phosphate is a different cell chemistry, common in China and often used with high power low range applications (buses/trucks). LFP is different to li-ion but neither worse nor better. It charges/discharges very easily, has an exceptional cycle life (you can charge/discharge many times with very little degradation) but at a cost of being less energy dense, so you need more volume to fit the same capacity of battery. You can very roughly equate cycle life to total lifetime mileage of the car - more cycles is more miles before pack needs replacing.

This makes sense for SR+ model, it has space for a very large li-ion battery so using less energy dense LFP Tesla can still achieve the required energy capacity that the SR+ model spec requires. i.e. SR+ with LFP has a bigger battery volume than SR+ with Li-ion.

Interestingly because LFP can discharge so rapidly, Tesla could probably make this model faster without undue harm to the battery. I expect they don't do this purely to keep model performance differences as a marketing ploy, not that the SR+ is slow anyway.

The car probably has an internal buffer, i.e. unused capacity at both ends of the voltage range of the cell. So when you charge to 100% it is likely actually less than this in reality. Same on discharge, when it states 0% they'll be a little left - evidenced by Carwow driving for miles after hitting 0% in their tests. High buffer helps protect the battery in early days and then can be used as the battery does degrade to maintain the stated range. So as capacity diminishes, move towards filling the battery to the real 100% capacity. On the 0% end of the capacity, by leaving some spare energy in reserve, you avoid the car damaging the cells as it continues to discharge to varying degrees when not in use. I expect at some point the car will completely turn off to protect the battery which will need some additional measures to open the charge flap and reenable charging (guessing). LFP models will likely 'supercharge' more easily than the Li-ion cars, certainly at a cell level they absorb energy far more readily but the car software will control it. There is a relationship here though with capacity, a larger battery (LR/Perf) can charge faster than SR+ simply because it has a bigger bucket to fill, so even though the SR+LFP has faster charging capability, because it is a smaller bucket it may actually charge at a similar or slower rate to the bigger siblings. It should however charge faster than the SR+Li-ion.

80% is often cited as an optimal charge level. This is a compromise but a good one - the less energy you store in the battery the more relaxed it is and the less damage caused. Think of the cell like a balloon filled with water, you can fill it to absolutely full but it'll be very stretched and tight and will become weaker - best analogy I can think of! If you can get away with only 50% in the battery and comfortably do all your journeys, then do that and recharge to 50% each day, it will benefit the pack. 80% means you get decent range and helps not stress the battery. 100% is for the days you are doing a long journey and want decent buffer to reach the next charging stop - I've charged my M3LR to 100% twice times in 18 months and even then it wasn't really necessary.

Another aspect of 80% is this is about the point that the pack reaches full charge voltage and switches from a constant current to constant voltage phase. Details are easy to find on the net but in simple terms, charging slows down from about 80% capacity, you'll see this if you watch it at a supercharger. This is why if you can charge to 80% or less and have enough range to get to the next supercharger, that will probably be quicker than charging to 100% and putting less charge in at the next charger or destination when you don't care anyway. As chargers get busier you could hypothesise that Tesla may start nudging up the kWh price after 80% charged to encourage drivers to move off to free up pumps. Note at home on a regularly 7kW charger you won't see this slowing of charge as the rate is already very slow compared to what the battery is capable of accepting.

Charging to 100% for LFP makes some sense, as said they have impressive cycle life even with full charge and discharge, so it will degrade the cell but by an appreciably smaller margin than for the Li-ion pack. By way of example, li-ion based cells get somewhere around 500 cycles before they are judged end of life (which in battery world is actually only 80% of original capacity). LFP will often achieve 2000 - 5000 cycles. Hence why Tesla isn't bothered about you charging to 100% to maximise range as you'll still get more cycle life. You can do the sums but even with 500 cycles of ~200 miles range, that's a 100,000 mile battery that's only lost 20% of capacity -ish. With the SR+LFP model, you're probably going past 500,000 miles before that happens.

The remaining range of the car is a very challenging prediction that the car computer makes and will constantly update. For most lithium based rechargeable systems an occasional 100% charge helps calibrate the algorithm that determines capacity remaining (and thereby range). Otherwise the car is trying to track capacity without a good known starting point. That means it is constantly trying to monitor exact energy consumption at all times (including when not in use) and estimate what is left. Add in that it has to predict temperature as this has an effect of the battery and car efficiency, as well as the parasitic drains on the battery e.g. if it is very cold tomorrow, it won't go as far as it is currently predicting today. ICE cars are no different, they use more fuel for the same journey if it's colder, or if the driver simply chooses to travel more quickly. I suspect that people never gave much thought to the predicted range remaining on their old diesels as it made no difference if you just needed to refill a little earlier given how fuel is so readily available. Remember in the end the range is only a guess and it has no real reflection on the actual true capacity of the battery. I would argue that charging to full and draining to nearly empty to 'calibrate' the range is futile and only helps the human feel better, it doesn't make any difference to the battery itself.

So called phantom drain is a thing, the car uses energy when it's sat doing nothing. Especially if it *is* doing something like cabin pre-heating or Sentry Mode or downloading an update and so on. This is a bit different to your old ICE dinosaur which did tend to do truly nothing when turned off, but then it didn't get regular updates, watch for intruders, defrost the screen while you were eating your cornflakes and so on. Also remember that whilst you have 'paid for' the lost miles, by comparison you've paid a lot less for the actual miles you have journeyed compared to an ICE car so let it slide!

As many others have mentioned, once you're past range anxiety and switch to percentage remaining rather than miles, you'll quickly get used to charging when you need to and relying on superchargers for longer journeys. My own way of using my car is to charge to about 85% once a week timed to finish by the time I'm about to do a commute. This journey gets the car below 80% and I carry on through the weekly commutes. I can usually get a full week of work and back plus a bit of pottering at the weekend from a single weekly charge, particularly as it gets warmer. I tend to not let the car dip below 20% purely because of the reduction on the GO pedal but there isn't any reason not to go lower. You can charge more frequently without any detrimental affect, I just avoid it because it's not necessary and is one less thing to do. With what I now know, I could have leased an SR+ and it would have been absolutely perfect and not affected me very much at all - a few more charges on the long journeys but nothing that I couldn't have managed. Trouble is, now I've had the LR and got used to the performance of it, tough to go back to anything slower next time.

Great write up. Thanks. Questions for you/others:
1. Thoughts about cold weather/charging/etc.
2. If you get a LFP - and it needs replacement (understand unlikely) -- but does it have to be replaced with LFP or could someone easily drop in a li-ion?

 

[ACarneiro]

500 cycles longevity for a Li-Ion battery?
I hope my P- battery lasts a LOT longer than that, I’m hoping to keep it for at least 10 years and my commute to work is 100 miles, so I use anywhere between 40% (summer) and 50% (winter) battery to get there and back…

 

[MrBadger]

500 cycles longevity for a Li-Ion battery?
I hope my P- battery lasts a LOT longer than that, I’m hoping to keep it for at least 10 years and my commute to work is 100 miles, so I use anywhere between 40% (summer) and 50% (winter) battery to get there and back…

Keeping things simple, battery cycles are normally regarded as a full cycle, so half a charge is half a cycle.

Again, keeping things simple, if your car has an average range of 200 miles (based upon 100 miles/50% winter range), then 500 cycles should have a minimum useful lifespan of 100,000 miles - it wont suddenly stop working at that mileage, just carry on with deteriorating range. Broadly in line with the battery warranty. You will also see that a LR and Performance have a higher mileage warranty, primarily due to them having a longer range over a full cycle.

Also a reason why there is a finite useful lifetime kWh capacity on home storage.

 

[WKZ12]

I work in the battery world but other opinions...

This was a really interesting read and about the best explanation I've came across.

It also makes me happier about my plan of keeping my Tesla Model 3 SR+ MIC I've ordered until it literally stops working some day in the far far away future.

 

[ItsNotAboutTheMoney]

and yet my car actually came up with a warning message the other day about repeatedly charging to 100% having an adverse affect on the batteries...

Honestly wonder if we will ever know for sure what the right approach is.

You have a long-range Model 3. The LFP is currently used in the SR+. 100% being OK refers to the LFP.

 

[Darmie]

Great information here. Thanks for the post. I will say it's a great to see them getting away from cobalt. One less FUD to be harping on.

 

[ItsNotAboutTheMoney]

Great information here. Thanks for the post. I will say it's a great to see them getting away from cobalt. One less FUD to be harping on.

Expect a _lot_ more use of LFP. The key patents expire in 2022, which opens things up for global manufacturing and use.

 

[ACarneiro]

Expect a _lot_ more use of LFP. The key patents expire in 2022, which opens things up for global manufacturing and use.

Would be good to see Powerwalls using LFP chemistry. Energy density is less critical and longevity is THE thing…

 

[Peter 224]

This was a really interesting read and about the best explanation I've came across.

It also makes me happier about my plan of keeping my Tesla Model 3 SR+ MIC I've ordered until it literally stops working some day in the far far away future.

Likewise, I drive about 5000 miles a year. So the M3 battery should be good for 20 years.... when I'll be 90.
IF I'm still here.
So, my last car????