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Discussion Starter · #1 ·
I have had my M3 AWD LR for less than 2 months and driven less than 2,000 miles. Only done one 150kw supercharger session for 20 minutes otherwise it has always been charged at 6kw at home. Followed all the guidelines about charging to 80% max except for a few 100% charges before long trips, and left it plugged in overnight etc.

Just installed the app My Tesla Core and was surprised to see that it shows battery degradation of 2.6% after such a short period of time.

Is this usual?
 

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Ioniq 5
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How is this figure derived?

It could just be the effect of cold weather means there is less apparent capacity based on voltages measured.

Or something like that. :)
 

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Discussion Starter · #4 ·
Possible that it might just be unbalanced battery cells. Try this and see if this resolves the issue:

Alternatively, could it just be the cold weather?
Thank you. I will try charging to 100% and leaving it plugged in (like I used to do with my Nissan Leaf!) to balance the battery as I've only done 100% charges with scheduled departure which always finishes at about 6am as it thinks we all have low cost electricity rates!
How is this figure derived?

It could just be the effect of cold weather means there is less apparent capacity based on voltages measured.

Or something like that. :)
I'm not sure how the My Tesla Core app does the Degradation calculations?
 

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3rd party apps are generally a joke really - they all extrapolate information from the API which doesn't tell you much more than the Tesla app and charge you for it, while having access to your car. You may have guessed I'm not a fan.

It's possible that your issue is the BMS needs calibrating. More detailed instructions below but essentially you need to leave the car over night at lower states of charge when you can so it can do its maths better. Its one of those things that is in conflict with the "always be charging" mantra some people recommend.

I'd avoid that video if its recommending 100% charge.

 

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I wouldn't believe anything one of those apps say.. 'degradation' isn't a value the Tesla API tells them, they're guessing.

What does your mileage say at 100%? Should be about 320 miles IIRC.
 

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Discussion Starter · #8 ·
3rd party apps are generally a joke really - they all extrapolate information from the API which doesn't tell you much more than the Tesla app and charge you for it, while having access to your car. You may have guessed I'm not a fan.

It's possible that your issue is the BMS needs calibrating. More detailed instructions below but essentially you need to leave the car over night at lower states of charge when you can so it can do its maths better. Its one of those things that is in conflict with the "always be charging" mantra some people recommend.

I'd avoid that video if its recommending 100% charge.

That app is free to use but I take your point.
To be fair battery SOC is still a guess, based on other parameters.
Here's a screenshot of the app screen showing the Degradation.
To be fair battery SOC is still a guess, based on other parameters.
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Battery degradation happens on an S-curve - it will be steepest from new, then it will level out after 12-18 months, be fairly flat for a LONG time, then start to drop more rapidly as the battery comes to the end of its life.

You can affect how quickly it occurs by your behaviour - prolonged high temperatures are bad, prolonged high charge is bad.

However, what tends to occur more with Teslas is that the BMS simply doesn't know what's going on. The battery needs to balance itself at diffent SoC levels (eg 20%, 30%, 40%, etc) for a period of time, and it can only do that when the car is sleeping - sentry mode prevents it from sleeping. There's also lots of people who plug it in every night (in fairness, the manual tells you to) and charge back up to 80% every night. The result of that is that the BMS knows really well how the battery is behaving at 80%, but everything else is a bit fuzzy...

I rarely plug ours in (only when actually charging - mostly 11kW at work or local free rapid when i pop into town). It sits at all sorts of weird %ages for days (past week it's been sat in the garage at 45%) so the BMS gets all the data it needs. Teslacore shows 2.92% degradation, on SR+ that is over 14 months old (June '19 build, August '19 registered) and 8k miles.

When I first got Teslacore (June 2020) it showed 4.58% degradation, but it had been a long time since I'd charged it up to 100% - i took it up to 100% then drove for abit and after a week or two it settled to less than 3% degradation. It has not been over 3% since then.

Given that our 24kWh Leaf was at 88.4% SoH (ie 11.6% degradation) at 30 months old and 13k miles, I'm pretty happy. I anticipate that the degradation will level out at somewhere around 4% once I get onto the flat bit of the S-curve. Given that over the 19 months we had the Leaf, and added 12.5k miles to it it dropped from 88.4% to 87.99% (worst ever seen) SoH, I'm fairly confident that I can look after a battery well. I anticipate maybe 5% by 5 years old.

So, the point is that you need to make sure that the BMS has full data available to it. Teslacore simply derives the degradation figure by comparing hte current "full range" figure to the as new full range figure. Make sure it gets to balance (sleep) at various SoC levels, and very occasionally 100% balance it. Most of the "degradation" you'll be seeing is BMS data lacking rather than true degradation, but also remember that a larger chunk of the degradation happens from new in the first year.

See also:

 

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Ioniq 5
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That app is free to use but I take your point.

Here's a screenshot of the app screen showing the Degradation.

View attachment 138126
Which tells us nothing. It may just be comparing rated range reported by the car with what the EPA value is for that car.

So still just an estimate.

Just enjoy the car and stop worrying. Things will wear if you use them.
 

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I have had my M3 AWD LR for less than 2 months and driven less than 2,000 miles. Only done one 150kw supercharger session for 20 minutes otherwise it has always been charged at 6kw at home. Followed all the guidelines about charging to 80% max except for a few 100% charges before long trips, and left it plugged in overnight etc.

Just installed the app My Tesla Core and was surprised to see that it shows battery degradation of 2.6% after such a short period of time.

Is this usual?
You dont have the new LFP batteries out of China do you? Or are these just in the SR+ ? The article mentions EU models reaching our shores around now.

 

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LFP are only in SR+ as they physically won't fit in an LR - USA SR+ have a 1/3rd empty battery box, whereas the LFP SR+ have a full battery box because of the lower energy density.

The LFP batteries are apparently very robust in terms of charge speed and tolerance of 100% charging, but they are heavier and dislike the cold.
 

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LFP are only in SR+ as they physically won't fit in an LR - USA SR+ have a 1/3rd empty battery box, whereas the LFP SR+ have a full battery box because of the lower energy density.

The LFP batteries are apparently very robust in terms of charge speed and tolerance of 100% charging, but they are heavier and dislike the cold.
I assume the TM3 has a preheat function like my Chevy Volt mk1 does? If you dont preheat the Chevy pack this time of year it will struggle above 2m/kwh as the car sucks energy to heat the pack on the fly, vs 3-4m/kwh at temps 15-30 degrees c with no preheating.
 

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Discussion Starter · #15 ·
Update. I just charged the car to 100% and left it plugged in (not for scheduled departure). After 45 minutes, I just rechecked the app and the degradation has gone down to 1.29% - see screenshot. So the BMS must be doing something.
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In my experience, temperature makes no difference to the degradation figure reported by teslacore. The bms balancing is the thing that keeps it under control.
 
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