Why is 85% battery recommended as the normal maximum?

[PanameraFrank]

You're 100% fine charging the battery to 100% if you intend to drive it down to 85% or less within 24 hours or so.

Just don't leave the battery at 100% charge for extended periods of time.

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[Cilviloze]

The battery capacity is
93.4 gross capacity (100%)
83.7 net capacity (90%)

Which means when you charge to 100% it actually means 90% of gross capacity.

Now for those of you who regularly drive a hybrid car, if you pay attention to how it charge/discharge battery, you may recognize that it keeps SoC between 4x%-7x% most of the time. That is the true sweet spot in term of durability.

Now do the math, 85% of 90% is 76%.

This is why Porsche want you to charge up to 85%.
It's the upper bar of sweet spot I guess.

 

[evanevery]

The battery capacity is
93.4 gross capacity (100%)
83.7 net capacity (90%)

Which means when you charge to 100% it actually means 90% of gross capacity.

Now for those of you who regularly drive a hybrid car, if you pay attention to how it charge/discharge battery, you may recognize that it keeps SoC between 4x%-7x% most of the time. That is the true sweet spot in term of durability.

Now do the math, 85% of 90% is 76%.

This is why Porsche want you to charge up to 85%.
It's the upper bar of sweet spot I guess.

I don't believe its that simple. I have seen several postings here on this forum indicating that not all of the reserved excess capacity (10%) is at the "top" of the charge. I'll let you search for the associated threads if you want to validate the info...

IOW: Some of the reserved capacity is at the bottom (you can't pull the actual charge fully down to 0%) and some is at the top (you can't fill the battery all the way up to an actual 100%).

 

[Scandinavian]

I do not believe there is much of a buffer at the top end.

There was a post here earlier about charging to nearly 100% and then driving downhill with regen on. When charged to nearly full there was NO regen, ie when you use your brakes the energy can not be stored. You will use the mechanical brakes. The battery can not receive the extra energy since it was full.

There was a second test where the battery hd a charge below 90% and then there was energy stored at the bottom of the hill. If you at that stage use the brakes it will mainly be regen.

I think that shows quite clearly that it is advisable to take Porsche’s advice to charge to 85% normally and to 100% if planning a longer trip.

 

[PanameraFrank]

@Scandinavian Correct me if I'm wrong, but if the battery is hard limited to think, say, 87 kWh of charge is 100% (leaving some inaccessible buffer on top) wouldn't it limit regen from exceeding that as well? You wouldn't put in a buffer and allow regen to exceed it, you'd also software limit the regen until it wouldn't hit the buffer.

Am I wrong on that? I'm not saying that proves or disproves anything, merely that testing that way is still inconclusive.

To be clear, this is proven in the iPace. Jaguar has clearly stated there is a buffer and you can not reach true 100% charge. Yet the iPace does not have regen when above 95% shown SOC.

 

[Gogs]

Porsche recommends 85% daily charge, the reason is really simple. At or near 100% the chemistry of the battery is unstable and is not good for the battery. So they say if you need 100% do not stay at 100% for long. Use your timer and set your charge requirement. If you need to claim on warranty, I bet that they will check charging logs and if you’ve ignored the recommendation then you’ll be paying for new battery cells. It’s not difficult to manage this and to be honest I don’t get the guys that talk about buffers and shit, it’s all drivel the book say 85, just do it!

 

[LonePalmBJ]

YMMV, but in eight years of EV ownership with a couple EVs in the household our approach is simply plug in when home and charge. No limits, no timers, no throttling. Every day starts at 100%. It's simple, and I've seen no appreciable battery degredation. I DC charge very infrequently, but for relatively-slow home Level 2 charging, my advice is to avoid overthinking it.

 

[PanameraFrank]

. If you need to claim on warranty, I bet that they will check charging logs and if you’ve ignored the recommendation then you’ll be paying for new battery cells.

This is categorically false and I'd ask you not to use scare tactics to try & prove your point.

EV battery warranties are guaranteed by % of capacity remaining vs the mileage/year figure. Charging has nothing to do with it and legally cannot be used to deny a battery health warranty claim, at least in the US.

(I've gone over this with a lawyer that specializes in auto/lemon cases and had my iPace bought back at full MSRP + extra for my trouble, specifically for diminished battery capacity. )

 

[Gogs]

This is categorically false and I'd ask you not to use scare tactics to try & prove your point.

EV battery warranties are guaranteed by % of capacity remaining vs the mileage/year figure. Charging has nothing to do with it and legally cannot be used to deny a battery health warranty claim, at least in the US.

I don’t need to prove any point. The manual tells you to daily charge to 85%. Feel free to charge to 100% and test a warranty claim.

 

[PanameraFrank]

I don’t need to prove any point. The manual tells you to daily charge to 85%. Feel free to charge to 100% and test a warranty claim.

See my (edited) post above. I've gone through this with a lawyer that specializes in auto/lemon law and had an iPace bought back above MSRP.

Diminished battery health is very specifically covered and very specifically how/when/where/why you charged the car has no impact.

 

[evanevery]

YMMV, but in eight years of EV ownership with a couple EVs in the household our approach is simply plug in when home and charge. No limits, no timers, no throttling. Every day starts at 100%. It's simple, and I've seen no appreciable battery degredation. I DC charge very infrequently, but for relatively-slow home Level 2 charging, my advice is to avoid overthinking it.

So, what car are you doing this with?

I'm on my 4th EV and the only ones we topped up (100%) regularly are plug-in hybrids with very small battery packs (Chevy Volt, BMW i8)

As far as "full" EV's go, Tesla officially recommends 90% for a daily charge and Porsche officially recommends 85%... For 5 years, we have been plugging in our Tesla every night (and whenever its in the garage), but Tesla specifically recommends setting a daily (nightly) charge limit of 90%. So we just set it to 90% and forget it. (We only need to temporarily change that setting if we have a long drive the next day).

Im curious what EV you own that officially recommends nightly charging to 100%?

 

[DragonRR]

Porsche recommend an 85% maximum charge to prolong the life of the batteries. They don't suggest anywhere that you have to do this so if the batteries fall out of manufacturers reasonable tolerances within the warranty period they will not be able to use the fact that you always charged to 100% as a legal argument. However this doesn't mean that you should always charge to 100% because eventually this really will reduce the life.

As far as a buffer is concerned - this has been discussed in at least one other thread:
https://www.taycanforum.com/forum/threads/how-to-set-to-profile-to-only-charge-to-85.1858/page-4

Apparently Porsche reduced the buffer and the reasonable estimate at the moment is around 4% on the bottom but only 1% on the top. If this is true then charging a Taycan to 100% is pretty damned close to 100%.

Overall the battery tech in my iPhone is unable to provide more than a year or so of 100% charging before overall life is reduced. My partner's 3 year old iPhone X was down from more than a good full day of use when new to having to charge it at luncthime every day.

Battery tech is still a work in progress. Personally I think charging to only 85% is an annoyance especially in a Turbo S but needed.

 

[evanevery]

...Personally I think charging to only 85% is an annoyance especially in a Turbo S but needed.

IMHO: It's only an annoyance if you don't "set it and forget it"...

 

[felixtb]

IMHO: It's only an annoyance if you don't "set it and forget it"...

on the Turbo S the mileage is pretty low so it does become an annoyance since you reduce an already low mileage by another 15%..........

 

[svp6]

This keeps coming back. Again, only Porsche knows what buffer they have and how that is split top / bottom. As I showed before, regen is much more wimpy at 100% than at 85%, which suggests there is little buffer at the top - if any at all.

Here is why I only charge to 85%
1. Battery degradation is faster when charging to 100%, especially if your battery stays fully charged for some time.
2. As you well know, the Porsche connect app keeps track of your charging history. I would seriously doubt that Porsche will care one bit about complaints of range loss if they can show you charged to 100% frequently. Why should they cover the repair / replacement if you specifically did not follow the recommendation and they can easily prove it? So use it at your own risk - if you are as unlucky as some of the infamous Tesla 90D owners who lost substantial battery range in short time, good luck complaining.
3. I do not miss at all the top 15% for daily commute.
4. If I travel next day, I have a "travel" profile that charges to 100% so I use that instead of 85%.
5. If I forget to charge to 100% the night before the trip (happened to me), I will spend almost 5 more minutes at the fast charger to catch up.

In short, the only 2 circumstances where I think you absolutely must have 100% charge are super-long commutes or trips where you need those extra miles to make it to the charger.

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