[JoelC]

Ever since I got the performance upgrade on my Polestar 2, I like charging it to 90% — it lets me enjoy the extra power for longer now since the boost is disabled under 70%.

Why would they disable or lower the boost below 70%? I don’t understand the rationale.

 

[Jupiter7]

Why would they disable or lower the boost below 70%? I don’t understand the rationale.

Lower battery state of charge = lower voltage. Max power only available at higher voltages.

 

[KingArthur]

Wouldn't this depend on what the electronics and software is doing? As I understand things, the battery is not connected directly to the motor(s), indeed the motors are AC anyway and wouldn't even work if this was the case. So it could be a bit like 100% charge not actually being 100% of the battery capacity to allow for a bit of headroom by the BMS. It's probably also the reason that we can buy a performance upgrade that is purely software. In other words, there's a lot more going on than might appear from a simplistic anaysis of battery SoC. Also, I can't say I've ever noticed any difference in performance between 100% SoC and 15% SoC (the lowest I've ever got to), but perhaps that just means I'm not driving like a maniac all the time

As for the question posed by this thread "what is the correct charge level", this surely just begs a further question about the definition of "correct". 'Correct' for battery longevity? 'Correct' for performance? 'Correct' for range? 'Correct' to avoid worrying that I'm doing something wrong?

My take on this is that Polestar offer an 8 year warranty on the battery with no contractual conditions regarding how the battery is charged, which as we all know can vary a great deal from slowish AC charging to rapid fast DC charging. The only advice they provide is to recommend limiting charging to 90% in order to maximise battery life, but that's just advice and not a contractual condition. So, I take this as meaning that if I only ever DC fastcharge to 100% then the battery is still going to be in good condition after 8 years, unless it is faulty in which case the warranty would kick in. Assuming the warranty is pessimistic, as most are, I'm not losing any sleep over the 'correct' way to charge it.

For the record, I mostly AC charge at 7kW to 80% at home unless I have a long trip in which case I charge to 100% the night before, and I avoid DCFC as much as possible, not so much for the battery's sake but simply because it's about 10x more expensive than using my home charger!

 

[JoelC]

All great points.

As the OP, I was asking the question in terms of longevity but am interested in the other aspects that you raised as well (i.e., for longevity, for performance and for range).

 

[Polarbear]

It was 80% just like tesla in the beginning, then they wanted to sell more cars and changed it to 90%.
90% is just marketing

 

[poundsnpence]

Obviously if you have home charging and don't need the full capacity of the battery there's no need to do any potentially harmful practices, but generally speaking, the worst possible thing you can do to your EV battery is leave it for an extended time at either very high or very low state of charge.

Most important of all: you've bought (or leased) a car - use it for the purpose you have it and don't let perceived battery deg stop you from doing so. Eventually second hand buyers will accept they are buying a used product that may not have the original advertised range - just like very few ICEs will be capable of achieving out of the factory performance or mpg when they've been used for a few years, or a second hand iPhone might not last you two days on a charge like a new one could.

 

[krheinwald]

Ever since I got the performance upgrade on my Polestar 2, I like charging it to 90% — it lets me enjoy the extra power for longer now since the boost is disabled under 70%.

It is not suddenly disabled @ 70%, it decreases below 70% until it disappears @ 40% - or I/my car missed a bulletin.

 

[Nobby Plumbs]

I charge mine to 100% every single day, just for the hell of it

 

[Vaporwave]

The most important factor is to minimize the time your battery spends above certain thresholds, where there is a sudden increase in wear.

For NMC those are at around 60 % and around 95 %.

Due to buffer and degradation, this equals about 55 % / 90 % displayed SoC.

Ideally, keep the SoC at or below 55 % SoC for as much as possible. When travel requires more, just charge more, as it doesn't matter much then in the grand scheme of things.

For extra care, a lower SoC is beneficial so optimal long term storage SoC is around 20 to 30 % SoC. However at normal temperatures (25 C) it's only really relevant to minimize the time beyond 55 %, no much difference below.

 

[Kojak]

What is NMC please?

 

[Kojak]

So is this how it goes then?

Mr Polestar: "Hi Mr Customer, thanks for buying your car with an 82KWh/220kw battery. Here have this new winter coat."
Mr Customer: "Really ? thanks what's that for?"
Mr Polestar: "For when you are putting your car on charge."
Mr Customer: "Sorry, I'm a bit lost. I just nip out occasionally and plug it in right?"
Mr Polestar: "Sort of, but you should be keeping the battery state of charge at less than 55%"
Mr Customer: " Go on then what's the punch line? the manual recommends 90% thats OK isn't it?"
Mr Polestar: "Ummm.....It is but really what we haven't told you is that 55% to 90% you are doubling the aging and increasing degradation rate".
Mr Customer: "So, I thought the 90% took care of the battery? are you telling me it's not?"
Mr Polestar: "Well, just charge to 90% when the journey needs you to."
Mr Customer: "That was my understanding for when to charge to 100% and that 90% is fine the rest of the time."
Mt Polestar: "55% and under is better."
Mr Customer: " So for everyday use then, preserving the battery, the WLTP figure of 409 miles should be changed for real world representation to something that aligns with 55% of that if you want to look after the battery? which in my rough calcs is WLTP of about 210 miles or in reality in mid winter considerably less? maybe 140 miles or so?"
Mr Polestar: "Something like that"
Mr Customer: "140 miles is naff all, I'll need to charge way more often if thats the case, especially in the winter."
Mr Polestar: "Try your coat on, lets see how it fits."

 

[KingArthur]

Also, I've seen battery specs that include the number of charge cycles they can support. So, if we only charge our batteries to 50% then surely we'll be doubling the number of charge cycles for a given mileage/lifetime, which might also be bad for them.

Frankly, it seems to me there's a lot of 'urban myths' flying around about EV batteries and it's difficult to see the wood for trees. I presume that battery researchers and EV manufacturers have spent billions developing this technology so where's all the real scientific data about it? Or are we really reliant on the modern equivalent of 'a bloke down the pub' for information?

Again, given that the only advice Polestar offers is to 'recommend' only charging to 90% while still offering an 8 year battery warranty (along with most EV manufacturers), my feeling is that it doesn't really matter how we charge.

 

[systemlogicblah]

… and all this hand wringing contributes greatly to EV hesitancy.

If I had really done a deep dive into this place before buying one, I probably never would have taken the plunge. Follow the general guidelines, don’t purposely abuse it, and just drive it. It’s a car. I feel like everyone way overthinks this.

 

[The Illustrative Man]

Also, I've seen battery specs that include the number of charge cycles they can support. So, if we only charge our batteries to 50% then surely we'll be doubling the number of charge cycles for a given mileage/lifetime, which might also be bad for them.

Frankly, it seems to me there's a lot of 'urban myths' flying around about EV batteries and it's difficult to see the wood for trees. I presume that battery researchers and EV manufacturers have spent billions developing this technology so where's all the real scientific data about it? Or are we really reliant on the modern equivalent of 'a bloke down the pub' for information?

Again, given that the only advice Polestar offers is to 'recommend' only charging to 90% while still offering an 8 year battery warranty (along with most EV manufacturers), my feeling is that it doesn't really matter how we charge.

"Charge Cycles" are 0-100%, so charging from 25-50% twice is the same as charging 25-75%, on that specific thing.

A lot of this is typical gearhead pedantry though. The same kind of stuff where people run different oil with more frequent changes, replace "lifetime" gearbox oil, run higher octane fuel than required, use the fuel additives, handwash vs carwash, etc. All of these things absolutely add up over the 20 year life of a car, but at the end of the day it doesn't matter for 99% of the population. The problem is with EVs this stuff has gained media traction, so all the non-gearheads are thinking about it.

We're nerds talking nerd stuff. It's a car, just drive it. If you want the super distilled "change oil every 3k miles" equivalent, it's "stay as close to 50% state of charge as possible without inconveniencing yourself".

 

[krheinwald]

I guess it's time to post this document again...

TL;DR: Stay as close to/around 50% as feasible.

 

[Vaporwave]

Again, given that the only advice Polestar offers is to 'recommend' only charging to 90% while still offering an 8 year battery warranty (along with most EV manufacturers), my feeling is that it doesn't really matter how we charge

For 8 years, it doesn't matter. However, you target may not necessarily be identical with the ones of the manufacturer.

 

[Vaporwave]

So is this how it goes then?

Mr Polestar: "Hi Mr Customer, thanks for buying your car with an 82KWh/220kw battery. Here have this new winter coat."
Mr Customer: "Really ? thanks what's that for?"
Mr Polestar: "For when you are putting your car on charge."
Mr Customer: "Sorry, I'm a bit lost. I just nip out occasionally and plug it in right?"
Mr Polestar: "Sort of, but you should be keeping the battery state of charge at less than 55%"
Mr Customer: " Go on then what's the punch line? the manual recommends 90% thats OK isn't it?"
Mr Polestar: "Ummm.....It is but really what we haven't told you is that 55% to 90% you are doubling the aging and increasing degradation rate".
Mr Customer: "So, I thought the 90% took care of the battery? are you telling me it's not?"
Mr Polestar: "Well, just charge to 90% when the journey needs you to."
Mr Customer: "That was my understanding for when to charge to 100% and that 90% is fine."
Mt Polestar: "55% and under is better."
Mr Customer: " So for everyday use then, preserving the battery, the WLTP figure of 409 miles should be changed for real world representation to something that aligns with 55% of that if you want to look after the battery? which in my rough calcs is WLTP of about 210 miles or in reality in mid winter considerably less? maybe 140 miles or so?"
Mr Polestar: "Something like that"
Mr Customer: "140 miles is naff all, I'll need to charge way more often if thats the case, especially in the winter."
Mr Polestar: "Try your coat on, lets see how it fits."

There is not only one optimization target.

Polestar will - reasonable speculation from my side - optimize variables so that the battery will have 70 % or more after 8 years (garantuee) while under the constraint of having the car and charging instructions as simple as possible.

They will internally have more complex models, together with CATL, but the above is a reasonable minimum because for sure they want to avoid battery replacement cost during the garantuee.

Your goal may or may not be identical to the ones of Polestar or it may overlap.

 

[Vaporwave]

I guess it's time to post this document again...

TL;DR: Stay as close to/around 50% as feasible.

Yes, that's a good one.

 

[Vaporwave]

. I presume that battery researchers and EV manufacturers have spent billions developing this technology so where's all the real scientific data about it? Or are we really reliant on the modern equivalent of 'a bloke down the pub' for information?

It's not speculation, there is scientific data.

While the general model is reasonably understood, there is uncertainty regarding the weight of some though, making it harder to give concrete recommendations.

The main difficulty though is, that with every model that has more than one or two parameters, it's no longer possible to compress it into one sentence that's understandable for the general public.

With batteries, there are plenty:

• chemistry
• temperature
• charging speed
• discharge depth
• SoC
• ...

Probably it's a couple of dozen.
Many of them are also not simple parameters but depend on other variables, are a function of time etc.

In addition, the model has to be translated and incorporated into user language and the users usage style. One consequence is, that there may be not one optimal solution but multiple, depending on e.g. the user weighs battery degradation vs convience.

For example, when the user is sure to give away the vehicle after 4 years to the leasing bank, his or her goal is easily achieved, no matter how charging is done, because it's very hard to shred the battery below 70% in 4 years.

To make an analogy: it's like asking "how do I invest my money in best way?".
Well, also here, the general models are understood enough that reasonable recommendations are possible that at least will prevent catastrophic outcomes.

However, it depends on your age, income, wealth, family size, place of living, investment goals, spend, ...
=> The simple question gets complex rather quick.

 

[Vaporwave]

Frankly, it seems to me there's a lot of 'urban myths'

Agree. Doesn't mean that there isn't scientific data, there is, but not all weights are exactly known and there are dozens of params, so it's easy to oversimplify.

This is for sure a contributor to urban myths (in addition to "simply wrong" statements taken over from different battery chemistries etc)