Battery Degradation

[docramage]

I am seeing several used Model s's this week with a view to purchase. While I think I understand the battery display, I need some advice.

The display shows the current mileage etc - but only I think in the current state of charge. If I see a vehicle showing - say - 50% battery charge, is there any indication of what the battery might achieve after a full charge?

In other words, how can I be sure that the salesman's assurance that the battery has only degraded to 90% is true?

It's difficult sitting at home with just a manual!
Many thanks

Philip

 

[jaguar36]

You can't.
The only way to tell is to charge to 100% and see, and even that can be somewhat deceiving as the BMS's calibration might be a bit off.

 

[thefortunes]

Maybe I'm misunderstanding your question, but the battery indicator can be changed to show % or rated miles.

If you have a car that shows 50% and you flip the display to rated miles and it shows 125 miles then you would have somewhere near 250 miles on a full charge.

I say somewhere near because you don't know if the 50% really means 49.6% or 50.4%.

Is that projection perfect, no, but it gets you in the ballpark.

 

[Troy]

Because you started this thread in the Model S section instead of the UK section, be prepared to get information that is not valid in the UK because the cars display different range numbers. In the settings menu, you can set it to display one of these:

• Percentage
• Rated (this means NEDC rated range in the UK and should not be confused with EPA rated range in the US)
• Typical

You should set it to typical because percentage doesn't tell you anything about remaining battery capacity and rated is not used outside of North America by any Tesla owner because it is completely unrealistic and overoptimistic.

Here is what a new Model S shows at 100% in the UK if you set it to Typical range which is the correct setting:

Model name, Typical range
Model S 60, 180 mi
Model S 60D, 207 mi
Model S 70, 224 mi
Model S 70D, 227 mi
Model S 75, 240 mi
Model S 75D, 241 mi
Model S 85, 249 mi
Model S P85, 249 mi
Model S P85+, 249 mi
Model S 85D, 267 mi
Model S P85D, 254 mi
Model S 90, 264 mi
Model S 90D (2015) 268 mi
Model S 90D, 281 mi
Model S P90D, 259 mi
Model S 100D, 320 mi
Model S P100D, 303 mi

US numbers are different. For example, a new Model S 85 has 265 mi and a new Model S 75D has 259 mi rated range in the US. Ignore these numbers and ignore numbers you have read if the threads were not in the UK section. Does this mean the cars in the US have more range? No, they have the same range. It is just a display difference. The Typical range numbers are more accurate but they are not available in the US. Typical range was created by Tesla. Be aware that the advertised range is not typical range. If you go to Tesla.com and look at the UK design studio, the numbers you see there will be the NEDC rated range numbers that are too unrealistic and nobody uses there. They are replacing NEDC with something better by September.

By the way, here is a degradation chart. Let's say you want to buy a used Model S 85 with 50,000 miles on it. At this mileage, average battery capacity is 95% which means 249 * 0.95= 237 miles typical range. Ideally, you should see something around this number at 100%.

 

[scottm]

There's also a thread here, "what's your range at 90%"... You'll have lots of data to compare with.. And can make a relative observation of your own among several model S's you drive.

You should ask each seller to have the car charged to 91% for your visit.

Drive the car mildly and note rated range as the car ticks down from 91 to 90 and then again when it goes from 90 to 89. Average the two.

Take a picture of the battery pack sticker (right wheel well area) as part of the records you're keeping. Just learn where the sticker is, and reach in with your phone to get a shot.

Post your findings!

 

[apacheguy]

My rated miles at 50% are almost exactly equal to half of the rated range at 100%.

e.g. 128 at 50 and 257 at 100%

 

[tnt1971]

My rated miles at 50% are almost exactly equal to half of the rated range at 100%.

This has always been my experience as well. I do notice the range is slightly less, at all charge levels, when it is cold. Top range is usually available over 70 degrees, ambient temperature. I have never experienced the "out of balance" condition that is discussed on the forum.

Also, make sure range mode is off. That does up the range a few miles at any charge level.

 

[Peter Lucas]

I am seeing several used Model s's this week with a view to purchase. While I think I understand the battery display, I need some advice.

The display shows the current mileage etc - but only I think in the current state of charge. If I see a vehicle showing - say - 50% battery charge, is there any indication of what the battery might achieve after a full charge?

In other words, how can I be sure that the salesman's assurance that the battery has only degraded to 90% is true?

It's difficult sitting at home with just a manual!
Many thanks

Philip

Here is a method to measure the useable capacity of a Tesla battery. The hard part is that you need to make some observations, then take a trip that consumes a significant portion of the total charge, like 25% at least, then make some observations at the end of the trip.
First, set the display to show battery percent, rather than range. Also, set the right hand part of the small display, in front of the steering wheel, to show the trip computer values. Then, at the start of the trip, make a note of the SOC, the battery percent. Take your trip. Should be at least 50 miles or so. More miles will increase the accuracy of the measurement somewhat. At the end of the trip take note of two things. First, the SOC (battery percent), and kwh used since start of trip. Also, take note of kwh used since the start of the trip. You can also find kwh used since last charge. This is useful if you started your trip just after unplugging. These numbers can also be found in the large display in settings.
Now you do a little bit of arithmetic. A very little bit.
Kwh consumed / (SOC start - SOC end) = total battery capacity
The SOC numbers have to be converted to decimal. So 90% becomes 0.90 and 25% becomes 0.25, for example.
Here is an example: I take a little trip. At the end of the trip, the trip display shows that I used 36 kwh. The battery display started at 80% and ended at 30%. 0.8 minus 0.3 is 0.5. 36 kwh divided by 0.5 is 72 kwh. Note that this passes the common sense test. One half of the battery capacity (80% to 30%) provided 36 kwh. So obviously 100% of the battery would provide twice as much, or 72 kwh.
Critics will state that the SOC measurement may not be linear. I checked. It is very linear. Not perfect. That's why making this measurement after a short trip will give somewhat unreliable values. 25% change of SOC is minimal. 50% should produce a very reliable value.
Note that the advantage of this method is that it doesn't matter how hard or fast you drive. Methods which measure range require you to also factor in your wh/mile. Unnecessary complication.

 

[docramage]

Many thanks for all your kind time taken to answer.

Am a bit wiser now . . .