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Charging percentage

There's a multitude of studies and experimentation done on real world battery performance. Charging to 100% of capacity vs 90% results in quite a large delta in remaining usable capacity after a certain amount of battery cycles.

I don't know the data on Tesla Powerwalls but the batteries in a datacenter UPS are supposed to be swapped out every 3 years for example, can you imagine if you had to do that for your car?
 

Saghost

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Oct 9, 2013
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Pushing a lithium battery towards either end of the range accelerates the wear - a battery that will do tens of thousands of 20-80% cycles will only do thousands of 10-90% cycles, or hundreds of 5-98% cycles - or tens of 0-100% cycles. Tesla doesn't expose the true 0% end - they keep around 5% as an anti bricking reserve, because if any cell gets pushed below 0% a single time, it will be permanently damaged. They pretty much do expose the true 100% though I believe.

Yes, you can charge the battery safely to 100%, especially if you don't leave it there for long. But why put wear on the pack when you don't have to?

It's highly unlikely that the 15 miles between 95% and 100% will ever be the difference between being stuck and not, so I don't go past 95% with the new Raven (and I only use around 20 miles daily, so I usually charge to 80%. I have seen that screw up the energy calculations and the car fix it when I pushed up to 90%, though.) I'm also trying to keep from going below 10% with it, successfully so far even on my 8300 mile road trip a couple months ago.
 
So, 20-80% charge cycle is optimum for battery life?
According to what I've read, high SoC of 90% vs 100% is a large, appreciable difference. Anything below that you're basically fighting for scraps. Something like 3-4% over 200k+ miles.

As far as the low end, I've seen Musk claim that there's zero risk in going to as low as 5% SoC. But then again he's also the one stoking the fires with the high end SoC with his 70% comments.
 
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Saghost

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Oct 9, 2013
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So, 20-80% charge cycle is optimum for battery life?

Closer to 50% is generally better, but the differences before 80% and 20% generally are so small you'll never be able to measure them according to what I've read.

The challenge is that 80% is still in the constant voltage section of the curve, so the BMS estimate of energy in the pack can get confused over time. I think that's why Tesla recommends charging to 90% sometimes - at 90% the cell voltage is out of the constant range, so the car can clearly see where the pack is, but you're putting a little more wear on the pack.
 
Why do people say that you must charge your car batteries to only 80%. We have Tesla batteries in our home and we charge them to 100%. Why the difference?
Elon Musk on Twitter
It’s not a big deal. Charge to 90% to 95% & you’ll be fine. At 100% state of charge, regen braking doesn’t work, because the battery is full, so car is less energy efficient.
 
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KenC

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Sep 4, 2018
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Why do people say that you must charge your car batteries to only 80%. We have Tesla batteries in our home and we charge them to 100%. Why the difference?
Different purpose, different usage. Plus the top/bottom buffers, are going to be different as well, so 100% for your Powerwall means something different than 100% for your car.

The design of a Powewall is less concerned about minimizing overall weight while the design of the battery for the car is very concerned about minimizing overall weight while maximizing usable battery capacity. Perhaps, it's a bit of marketing too, to say you have 335 miles of range, when for practical purposes, you're only seriously going to use at most ~90% of that, going from 100% down to about 10%.
 
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everything i've read in this thread supports most articles, discussions and reports i've come across so far. however, the one thing i'm not 100% certain of is this:

doesn't Tesla already "conservatively limit" the batteries in each and every vehicle to help protect the lifespan of the entire drivetrain? that is to say, 100% is not ACTUALLY 100%, etc. this is true in most li-ion battery applications as the charge rates/cycles for li-ion is so "poor" to begin with that by conditioning an acceptable "range" actually promotes a longer (artificial) lifespan of the battery.

for me, personally, based on the reports that the difference between 80% and 90% is so negligible that I charge to 90% on a daily basis. I have a 70-80 mile commute, every day, and am back and forth once I do get home on most days. based on my current 240kwh driving average, i'm usually home with a battery around 40-50%. could I live with 80%? probably. but I like the peace of mind and if the effects are so minute, i'm ok with my current SoC plan.
 

Rocky_H

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Feb 19, 2015
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I dislike Elon's quote about regen not working at 100%. It starts to limit at around 83% in my experience, and is quite noticeably limited above 90%.
You are just looking for dots to show that it is limited, but partially limited regen still isn't that much of a difference in driving feel. At 100%, it is downright startling when you pull your foot back off the pedal, and nothing happens as the car continues to GO like a runaway train! So that's why the quote has some relevance.
 

darth_vad3r

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May 6, 2019
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everything i've read in this thread supports most articles, discussions and reports i've come across so far. however, the one thing i'm not 100% certain of is this:

doesn't Tesla already "conservatively limit" the batteries in each and every vehicle to help protect the lifespan of the entire drivetrain? that is to say, 100% is not ACTUALLY 100%, etc. this is true in most li-ion battery applications as the charge rates/cycles for li-ion is so "poor" to begin with that by conditioning an acceptable "range" actually promotes a longer (artificial) lifespan of the battery.

I get the impression from reading around these parts that there's more protection at the bottom end compared to the top, if there actually is any at the top and instead they really let you go very near, or actually to, true 100% these days to max out the range at the risk of damage to the battery (which they warn you about if you repeatedly charge over 90%). With the original Roadster the blog 'a bit about batteries' said they didn't let the user go beyond 95%. This could have also just been earlier versions of the firmware, and now it might be the same on the Roadster too? I don't know anything about the Roadster's UI for charging.

Anyways, IF there is more protection at the bottom end, then if you back off X% from the top end you might actually be a bit closer to 100% than you think you are..

As an exaggerated example, if there was 9% on the bottom, and only 1% on the top, then the car's 0-100% would be from true 9-99%.

If you backed off 1% to 99% in the car, that would actually be only backing off a real 0.9% from 99% to 98.1%.
By the time you back off "10%" in the car to 90%, you are actually at "true 90%" as well.

If it was 10% on the bottom and 0% on the top, then backing off to 99% in the car is actually 99.1% in reality.

etc.

(btw, that blog for the Roadster from Nov 2006 says the opposite of what I'm describing with a 2% bottom buffer and 5% top buffer :))

for me, personally, based on the reports that the difference between 80% and 90% is so negligible that I charge to 90% on a daily basis. I have a 70-80 mile commute, every day, and am back and forth once I do get home on most days. based on my current 240kwh driving average, i'm usually home with a battery around 40-50%. could I live with 80%? probably. but I like the peace of mind and if the effects are so minute, i'm ok with my current SoC plan.

Yep, do what works for you. If it makes no difference to you, I'd side with lower just because "why not?". Like why not use SPF 50 instead of SPF 10 when you go in the sun?

I use ~20%/day of my SR+. I used to always go to 90. I do 70-50-70-50... now instead. I go up to 90 for a trip or for a weekend where I might get less charging in versus weekdays where I charge at work daily.
 
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