Charge to 90% or 80% daily?

[Zorak03]

I always charged my 12/18 mid range to 90% until around the first of the year when I reduced it to 80%. After that, like within a month, my projected range dropped from 264 down to around 240. I read somewhere that Charging to 80% while only doing short trips will throw off the BMS. I don’t drive much as I work entirely from home. Ive put less than 5000 miles on the car since I picked it up in December 2018.

Because of this, I’m considering raising my charge limit up to 90%. Is 90% daily ok for the battery? I keep my car plugged in when not driving it. 240 is more than enough to meet my daily needs, but from my understanding, if the BMS is off the car will shut itself down when it reaches the end of its projected miles even if the battery actually has more capacity. This could be a small issue when going on the occasional long road trip.

 

[Bubbatech]

The general consensus is to set if for 90% and forget it. The bms will not balance the bricks below 85%. As the bricks become unbalanced, the range indication will be determined by the brick with the lowest voltage.

 

[camalaio]

You'll find anecdotes on either side. Like recently, we started charging to 60% and only discharging to 50% and I've had the most significant degradation hit reported after that. We used to go through 30-50% of the charge every day depending on season, and frequently charged to 90% every night in winter.

Most people will agree that for these types of batteries in general, 90% is probably fine but 80% is better if it doesn't impact your life. If you need the extra 10% it's probably preplanned and you can adjust the limit prior to leaving.

@Bubbatech do you have a link with more info on that? Curiousity for myself, not at all a disagreement. Want to know more!

 

[Rocky_H]

The general consensus is to set if for 90% and forget it.

No it isn't "the consensus".

80% is better for the overall long term health of the battery and will make it last longer. But it will cause the BMS to get more and more fuzzy and inaccurate measurements of the energy over time, so the rated miles number that appears in the display will start reading artificially low.

Up to you which one is more important to you.

 

[Tam]

...do you have a link with more info on that?...

The receipt from Service Center for @Coolesnce clearly recommends changing charging habit "to 90%."

Youtuber also said Service Center told her so:

 

[Tam]

...if the BMS is off the car will shut itself down when it reaches the end of its projected miles even if the battery actually has more capacity. This could be a small issue when going on the occasional long road trip.

I think the BMS will attempt to recalculate the displayed miles on your battery gauge icon in real-time.

A drifted off calculation would underestimate the miles such as it's supposed to be 310 at 100% but it only displays 300 at 100% or 10 miles off, then your car still can drive for 310 miles despite the lower display.

BMS would attempt to correct itself as you drive, so it would revise the rated miles during the drive to account for that 10 missing miles.

Such as: Starting at 300 mile display, you traveled 155 miles so with the original drifted math it should display 145 miles left but no, it displays 150 left.

And with that 150 miles left, along the way, it would slow down the display loss to reflect that you actually can drive another 155 miles. That's a total of actual 310 miles despite original 310 display.

That means, if your car would shut down at 0 miles before the drifted calculation, your car will still shut down at 0 miles after the drifted calculation. Zero means zero (theoretically).

 

[camalaio]

The receipt from Service Center for @Coolesnce clearly recommends changing charging habit "to 90%."

Youtuber also said Service Center told her so:

The unfortunate thing is that when Tesla recommends this, it doesn't strictly mean it's because it's good for your battery. For example, a blanket recommendation to charge to 90% nightly could prevent some people from going down to 5% (as mentioned). The assumption here is that below 5% is worse than sitting at 90%. And Tesla needs to make blanket recommendations as the popularity of EVs increase - not everyone's checkin' out forums seeing what's best, but people want to get the max range. So 90% is a good number in that regard probably without complicating things, like we like to do on these forums

Tesla service centers also used to say the range display by the battery icon changes with driving habits, climate control usage, etc. which is completely false to the point Tesla sent out a memo about it so it's hard to find good info.

Elon has mentioned on Twitter (indirectly IIRC) that 80% is better than 90%, but not in a way that's significant to most people.

 

[Tam]

...Tesla service centers also used to say the range display by the battery icon changes with driving habits, climate control usage, etc. which is completely false to the point Tesla sent out a memo about it so it's hard to find good info...

Unofficially as an individual employee opnion, then, yes.

However, I believe those false information are not documented on an official Tesla Service Center receipt.

...Elon has mentioned on Twitter (indirectly IIRC) that 80% is better than 90%, but not in a way that's significant to most people.

Here's the tweet:

@LikeTeslaKim
Nov 30, 2018
@elonmusk
any insight on the best nightly SoC for battery longevity? 90%, 70%, 50%?
Any software fix for unbalanced cells due to sub 90% nightly charges?

@elonmusk
@LikeTeslaKim
Not worth going below 80% imo. Even 90% is still fine. Also, no issue going to 5% or lower SoC.
9:57 PM · Nov 30, 2018·Twitter for iPhone

She's asking for "sub 90% nightly charges" and as low as 50% which prompted the answer "Not worth going below 80% imo. Even 90% is still fine."

But note that the answer has "imo", an opinion, not a proven scientific fact.

 

[KenC]

If what you are currently doing is working, keep doing it. If what you are currently doing isn't working for you, then change it up. Seems obvious, but there doesn't seem to be any rhyme or reason why one charging strategy works for one vehicle, and not for another; and then the opposite strategy will work for the other vehicle, etc.

 

[jdw]

I charge to 90% pretty much every day, but only finish charging right before I leave, so the car typically spends < 1 hour at 90%, then sits at ~80% for 7 hours and ~70% or less for ~16 hours. I'm on my second Tesla over the last 5 years and both cars actually gained a small bit of range from when I picked them up. My current car shows a rated range increase of 0.25% after 12000km.

I have seen temporary drops in range when I have left the car sit for a week or more at 50%, but the range comes back in a few weeks of daily charging.

Point is, by charging right before you leave, you can get the best of both worlds - the BMS doesn't drift, the cells are balanced and the battery is not sitting at a high state of charge for a long period of time. I also never charge when the battery is cold. If I have to park outside in the winter and charge, I warm the battery first. I also reduce the charge or run the battery cycle deeper on really hot days to avoid high SOC & temp.

My Model S Teslafi chart - the dips are from when I leave the car sit at a low charge (50-60%) for a few days or more. The peaks happen after a few 90% charges. The drop towards the end was from leaving the car sit for a month at 50% - took a month+ and a 100% charge to get the BMS indicated range back up (plus it was winter).

 

[Sam1]

The app and car tell you to charge to 90% for daily use. Didn't know there were people arguing with tesla on how much to charge it on a daily basis versus on a trip.

 

[Bubbatech]

No it isn't "the consensus".

80% is better for the overall long term health of the battery and will make it last longer. But it will cause the BMS to get more and more fuzzy and inaccurate measurements of the energy over time, so the rated miles number that appears in the display will start reading artificially low.

Up to you which one is more important to you.

I agree that it is theoretically better, but the magnitude of that benefit has never been established. I really don’t care if the battery will last only 20 years rather than 30. Tesla service documentation says that the bms can compensate for 1mv Imbalance per day and that no compensation occurs below 85%. So while it is, in theory, better to charge closer to 50% for ultimate longevity, the design decisions for the bms suggest that they intend the car to be charged above 85%. Most people who buy the car will know nothing about lithium battery characteristics. The engineers are going to make the design compromises for them.

 

[user212_nr]

The receipt from Service Center for @Coolesnce clearly recommends changing charging habit "to 90%."

It says clearly "the true range is not affected".

 

[Resist]

It's always a trade off between range and battery health. If you're going to keep your Tesla for 10 years, then you want to keep the battery healthy for as long as possible. And if you're going to keep it less than 10 years and probably trade up, then charge it to 80-90% everyday and of course only to 100% just before you leave on a trip.

But honestly, set the battery display to show percentage and stop looking at the range display. An ICE vehicles fuel gauge is a percent of how much fuel is in the tank and that's how we should be looking at our EV's fuel gauge. And with so many charging options out there, we don't have range anxiety with a Tesla

 

[Tam]

It says clearly "the true range is not affected".

Very true. Thanks for pointing that out.

As I gave an example above of battery gauge that erroneously displays 300 miles when it should display 310 miles, the true range of 310 miles is not affected even though the drifted calculation displays a lower number.

 

[1.21GW]

90%

 

[Thunder7ga]

Why doesn't Tesla just state this clearly in the manual? I am shocked that after all these years they still do not have anything in there about the "best" for "recommended" levels.

 

[1.21GW]

Why doesn't Tesla just state this clearly in the manual? I am shocked that after all these years they still do not have anything in there about the "best" for "recommended" levels.

Tesla states their recommendation very clearly on the app.

50-90% - Daily
90-100% Trip

This is as clear as it gets. Everyone else is merely providing their opinion (I provided my own opinion as well)

 

[JBT66]

I’m personally very cautious of 90% charges. My car had a slow and steady decline.

I changed to 80% in the chart right as it bottomed out and slowly recovered some.
My usage here is basically driving 40 miles round trip and charging to 90%. This means my car would charge to 90% in about 2 hours and would sit at 90% most of its life.

the latest blip up is changing the wheels to 20s in the app while I’ve always and still do have 18s.

 

[Tam]

Tesla states their recommendation very clearly on the app.

50-90% - Daily
90-100% Trip

This is as clear as it gets. Everyone else is merely providing their opinion (I provided my own opinion as well)

Agree!

It's very clear that we should not worry about the health of the battery as long as we stick to the above parameters.

The 90% charge coming from Tesla Service Center is because owners keep complaining that they keep "losing" miles and their batteries keep "degrading" (It's just a more prominent calculation drift for sub 90% setting that has no effect on the battery real range or health).

90% charge is to minimize the calculation drifting and it has nothing to do with whether 90% is drastically healthier or worse than 50%.