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Should LFP batteries be charged to 100%?

SaffaT3sla

Member
Mar 28, 2021
12
3
St Albans
Got chatting to a few other Tesla owners at a supercharger today as they were interested in seeing my Chinese M3 SR+ and they said it has a new batter (LFP) and that the advice from Tesla is that LFP batteries can (and should, according to Tesla) be charged to 100% regularly, whereas the NCA battery should generally only be charged to 80%.

Is this true? The extra 20% would be useful on the SR+
 

Tigermad

Member
Mar 1, 2021
186
20
UK
Got chatting to a few other Tesla owners at a supercharger today as they were interested in seeing my Chinese M3 SR+ and they said it has a new batter (LFP) and that the advice from Tesla is that LFP batteries can (and should, according to Tesla) be charged to 100% regularly, whereas the NCA battery should generally only be charged to 80%.

Is this true? The extra 20% would be useful on the SR+
Yes, Elon has stated that the new battery is fine charged to 100% regularly. Obviously if you do this regen braking wont be in full effect.
 

Durzel

Active Member
Jul 17, 2019
2,833
1,858
Bath, UK
As I understand it MIC cars/LFP batteries remove the whole “daily” and “trip” advisories on charging, which would suggest that it’s fine to charge them to 100% every time.

As said above this would have an effect on regenerative braking.

The NCA batteries can be charged to 100%, my understanding is that the advice is not to leave it at a high SoC for extended periods. That being said I believe you get a warning popup in the car if you charge to 100% for 3 consecutive days.
 

SaffaT3sla

Member
Mar 28, 2021
12
3
St Albans
Fantastic, Thanks, everyone. With the standard range smaller battery every bit extra helps.

I'm assuming the regen would kick in fairly quickly anyway?
 

HenryT

Member
Jan 29, 2020
461
356
Manchester
Fantastic, Thanks, everyone. With the standard range smaller battery every bit extra helps.

I'm assuming the regen would kick in fairly quickly anyway?
There has been comment elsewhere on here, on the same subject, to the effect that there may be hidden buffer meaning that re-gen would be available pretty quickly?
 

SaffaT3sla

Member
Mar 28, 2021
12
3
St Albans
You tell us!! We're waiting to find out! :)
OK, so I charged the battery to 100% and we drove to London and back today (around 90 miles return). Regen was definitely not as strong and I used the brake a number of times on the way there but seemed much stronger on way back.

One thing I did notice (not sure if it's related) but my battery never actually got to temperature the whole way there and the dots only disappeared when we were almost home.

Is there a way to check that my heat pump is on or to pre-heat the battery before I leave the house?
 

Adopado

Active Member
Aug 19, 2019
3,294
2,457
Scotland
OK, so I charged the battery to 100% and we drove to London and back today (around 90 miles return). Regen was definitely not as strong and I used the brake a number of times on the way there but seemed much stronger on way back.

One thing I did notice (not sure if it's related) but my battery never actually got to temperature the whole way there and the dots only disappeared when we were almost home.

Is there a way to check that my heat pump is on or to pre-heat the battery before I leave the house?
It sounds like you had at least some regen at 100%. (Normally there would be none at all and there would be a message on screen letting you know about the lack of regen.) If that’s the case then it’s different to none lfe cars.

From what I’ve read and seen on Byorn Nylands YouTube channel there can be issues with how the heat scavenging affects battery temperature in heat pump cars so that could be related to not getting rid of the dots.
 

SaffaT3sla

Member
Mar 28, 2021
12
3
St Albans
OK, so another thing I've just noticed. I charged to 100% again last night but it's only given me 240 miles. What happened to the other 38 miles I paid for? (see screenprint attached)
 

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Adopado

Active Member
Aug 19, 2019
3,294
2,457
Scotland
OK, so another thing I've just noticed. I charged to 100% again last night but it's only given me 240 miles. What happened to the other 38 miles I paid for? (see screenprint attached)

I strongly recommend that you review the many threads that discuss the miles readout on the display. There's lots of info already on the forum. Suffice to say there are many many factors and it is such a guesstimate that many/most of us switch the battery display to percentage. (It's also not because you have a new type battery.)
 
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adsheff

Member
Sep 9, 2019
237
197
UK
I strongly recommend that you review the many threads that discuss the miles readout on the display. There's lots of info already on the forum. Suffice to say there are many many factors and it is such a guesstimate that many/most of us switch the battery display to percentage. (It's also not because you have a new type battery.)
I second that! Switch off the miles display it only serves to confuse and worry you. If you need an accurate guesstimate, use the Sat Nav and the Trip energy graph display instead.
 
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Adopado

Active Member
Aug 19, 2019
3,294
2,457
Scotland
use the Sat Nav and the Trip energy graph display instead.

... which works very well. When in Trip mode it's pretty accurate. It tries to take account of the actual route and gradients.

When just looking at the Energy Graph in Consumption Mode it also gives you some insight into the overall challenge of predicting range ... just compare the "projected range" on the basis of the past 5 miles, 15 miles and past 30 miles ... you get 3 significantly different figures .. so which is correct? They ALL are (or none are) ... it just depends on how you drive the next x number of miles!
 

Irata

Member
Oct 16, 2020
293
169
UK
OK, so another thing I've just noticed. I charged to 100% again last night but it's only given me 240 miles. What happened to the other 38 miles I paid for? (see screenprint attached)

At 100% charge it shows the EPA range, the 278 is WLTP. The manual does say that 100% charge is always EPA regardless of environmental factors.
 

Adopado

Active Member
Aug 19, 2019
3,294
2,457
Scotland
OK, so another thing I've just noticed. I charged to 100% again last night but it's only given me 240 miles. What happened to the other 38 miles I paid for?

Our Fiesta only does 50mpg; what happened to the other 20mpg I paid for? [Just an inappropriate jest ... but ... you know ... ;) ] In truth the electric car world probably does slightly better than the petrol world in representing its ranges but we're working with smaller margins so, understandably, it does make us panic a bit!
 
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mpandrew

Member
Sep 23, 2019
216
190
Somerset, UK
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.
 

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