How Big is my Battery ?

[GrahamW42]

I recently bought a CPO S90D first registered in the UK in Feb 16 – so I guess a Dec 15 build. It has 35,000 miles on the clock.

I’m now questioning the battery capacity and I’m trying to “prove” to myself that it had, as stated, received the “Range Upgrade” to 90kWh under a previous owner … and, more importantly, that the “Range Upgrade” was still in place for me !

The reason I took an interest is that my %age SoC moved in a way that suggested that I was only getting a “real world” range of 200 miles. I put this low figure down to freezing temperatures in December and January. However last week, in “balmy” 16C weather, I was still only getting 200 miles of range on a long cruise at 75mph.

So I tried to work out how big my usable battery was to the nearest kWh:


Method One

My Rated Miles @90% SoC is exactly 300 – suggesting a max range of 333 Rated Miles.

I looked VERY closely at the Energy App and determined that the “Rated” line runs at 240Wh/m.

So 333m x 240Wh/m = 80kWh


Method Two

I monitored the trip readings carefully and saw that as SoC dropped from 95% to 45% (exactly half the battery capacity) the energy used showed as 37.4kWh.

So 2 x 37.4kWh = 75kWh.


Method Three

Looking at the Energy App, I can choose between three calculations of the remaining range using historical average consumption. They are based on the last 5, 15 and 30 miles.

Knowing the SoC %age, these figures allow one to work out the assumed total battery capacity.

With each of these three calculations I get 78kWh.


So, which is my correct usable capacity; 75, 78 or 80 ?

And why are they all so far short of 90 – do I actually have a “Range Upgraded” battery ?

Or am I doing something fundamentally wrong in my calculations ?

Or do I need to do some sort of “reset” on my car to get “truer” readings ?

 

[dsnows]

The display in your car should indicate the current battery capacity. I bought a software locked 60D. The display in the car said 60D. When I upgraded to 75D, the display changed to indicate that. I did have to go get a new badge for the back of the car.

 

[ucmndd]

Method One

My Rated Miles @90% SoC is exactly 300 – suggesting a max range of 333 Rated Miles.

First suggestion: you likely have “ideal” range selected, which is incredibly optimistic.

Check this setting in controls -> display -> energy display.

 

[ucmndd]

As for the battery itself, your “90kwh” battery was actually 85.8 kWh when new, and about 81.8 kWh was available for propulsion.

 

[GrahamW42]

The display in your car should indicate the current battery capacity. I bought a software locked 60D. The display in the car said 60D. When I upgraded to 75D, the display changed to indicate that. I did have to go get a new badge for the back of the car.

Yes, it "should".

But I'm trying to "prove" it by understanding the various readings I'm getting.

 

[GrahamW42]

As for the battery itself, your “90kwh” battery was actually 85.8 kWh when new, and about 81.8 kWh was available for propulsion.

Ah. So if, as I suspect, the Energy App is right (78kWh) then I've lost ~5% of usable capacity in 35,000 miles.

Is that reasonable ?

 

[dhanson865]

Ah. So if, as I suspect, the Energy App is right (78kWh) then I've lost ~5% of usable capacity in 35,000 miles.

Is that reasonable ?

No it's not reasonable to think of it in terms of miles. You'll be able to reconcile with reality a lot better if you think of it in terms of months or years (the longer the time frame the better). Find the manufacturing date and count from there to now.

Heat and Time are the two primary factors for battery aging. And there is a steeper curve when the pack is new that flattens out some over time assuming heat is kept to reasonable levels.

Charge / Discharge Cycles are secondary and can be done without moving the car (climate control and vampire drain vs charging for example)

Miles isn't even on the chart as a reasonable measure if you normalize for the higher priority variables mentioned above.

Try and track your battery pack over 12 month so it incorporates all 4 seasons. Summer and Winter both do enough to mess with the degradation curve to make any attempt at short term comparisons invalid. Make your comparison Year over Year (readings taken in the same month of different years) and you'll have something worth discussing.

 

[GrahamW42]

No it's not reasonable to think of it in terms of miles. You'll be able to reconcile with reality a lot better if you think of it in terms of months or years ...

That's all great info - thanks.

So, do you think that it is reasonable to have lost 5% in 3.25 years ?

 

[dhanson865]

That's all great info - thanks.

So, do you think that it is reasonable to have lost 5% in 3.25 years ?

Yes.

My Nissan Leaf loses about 6 to 7% a year in TN, USA.

I'd be thrilled to only be losing 1 or 2 percent per year.

Keep in mind for accurate data you'll need TM-SPY Using TM-Spy to see Model S data.

but at that rate of loss I'd just charge my car and drive it.

 

[Dannyzuko]

Hope this helps

 

[GrahamW42]

Hope this helps

That's very illuminating - thanks.

I wonder how that differs to my (Range Upgrade) 90D ?

A previous post said that I had "81.8 kWh ... available for propulsion". I think, based on your chart, it may be slightly higher.

I've re-done my Energy App calc with better data and come up with 78.9kWh for my total battery capacity. If I only started with 81.8kWh then my degradation is only 3.5% in total ... for THREE YEARS+ !


On a separate issue, looking around this forum, I've not seen other people quoting "Rated Mile" ranges of anything like 333 miles. My car seems to use a very low figure of ~240Wh for each "Rated Mile". I'm surprised that no one has challenged me on my readings.

 

[Rocky_H]

On a separate issue, looking around this forum, I've not seen other people quoting "Rated Mile" ranges of anything like 333 miles. My car seems to use a very low figure of ~240Wh for each "Rated Mile". I'm surprised that no one has challenged me on my readings.

Your location is listed as "Thirsk", which I tried to look up. Is that the city in the UK? If so, that explains why the term "rated miles" is creating so much confusion.

The cars have two different types of settings for the distance display. In the U.S., "rated" is the lower one. In Europe, it's the higher one, so they don't correspond at all.
The U.S. has one called "ideal miles", which is way high. And then their lower one is called "rated miles", which is by the U.S. EPA efficiency standards, which are a little optimistic, but still fairly possible to achieve.

In Europe, their efficiency ratings system is NEDC, which is ridiculous, outrageous, fantasy that no one can hope to achieve, so it is the higher one that they call "rated". Their lower one, they call "typical".

 

[GrahamW42]

Your location is listed as "Thirsk", which I tried to look up. Is that the city in the UK? If so, that explains why the term "rated miles" is creating so much confusion.

The cars have two different types of settings for the distance display. In the U.S., "rated" is the lower one. In Europe, it's the higher one, so they don't correspond at all.
The U.S. has one called "ideal miles", which is way high. And then their lower one is called "rated miles", which is by the U.S. EPA efficiency standards, which are a little optimistic, but still fairly possible to achieve.

In Europe, their efficiency ratings system is NEDC, which is ridiculous, outrageous, fantasy that no one can hope to achieve, so it is the higher one that they call "rated". Their lower one, they call "typical".

Hi Rocky,

Yes, I'm in the UK.

I've only owned a Model S for about four months, but like most owners I've followed "all things Tesla" for several years. In all my research I never stumbled across this fundamental difference between two otherwise identical Teslas with different homes !

I've used your full quote and was going to trim it down for brevity ... but I can't find any extraneous words to trim. What an excellent post !

I wonder if anyone knows the actual Wh/mi used by European Teslas in the "Rated Mile" calculation ? It would allow me to convert my 333 Rated Miles into the usable kWh of my battery.