Battery Degradation

[GeorgeSymonds]

As we keep saying on this forum, that mileage is an estimate. You might even cover more total miles despite starting out at the 288 estimate than when you were getting a 309 estimate. Your short journeys are probably not helping the BMS to track where things are at because a relatively high percentage of charge will be being lost when the car is not driving. I would say that's almost certainly a BMS calibration issue.

Changing to percentage display rather than mileage is recommended. If it were me, and if I was worried enough, I would be doing some long runs, planning to get home with 10% and then charging to a mid/high 85% and doing the same but then take it to 100% on the subsequent charge and run down to 20% on longish mixed runs... but really this recalibration will happen over time anyway unless your car remains virtually unused!

Tesla use the EPA (US) range average consumption to show miles on the main screen (buit not energy screen) e.g. 40kwh available in the battery, 250wh/mile average EPA (4 miles per kwh) then 160 miles will be displayed This is why in the UK when fully charged you don't see the figure from the website even when new (lazy Tesla programming really not to use the local WLTP figure especially as when Europe used NEDC they knew that was way out so they introduced a local "typical" figure which some older cars still use. They should have just changed this to the WLTP figure)

As you say. what you actuallly consume when driving will vary and is highly unlikely to be 250wh/m so your actual mileage will differ, lower or higher.

As fopr % - I recall seeing a poll on the UK facebook group and it came out 1/3 went for %, 1/3 for miles and 1/3 didn't care. Anyone that tells you % is the right thing is just expressing there preference, there is no right answer its personal choice. its certainly NOT recommended by anyone other than some vocal people.

There is another way to calculate degradation without having to sign up to Teslafi just by taking 3 figures from your cars dash and comparing it to the useable battery capacity of the car. Understanding the logic here will also help understand the different numbers in the car

Tesla battery degradation and health - Tesla Info

 

[joanfa]

Hi,

would like to share my situation as well.

Car is around 1 month old and I've done 2,500 miles, charging mostly at home with the 3-pin plug and maybe 6-7 SC sessions of 15-25 minutes.

I charge the car to 90% normally, but done 2 full charges as well. M3SR+

Once new, 90% battery meant 214 miles. Now, 90% means 210 miles. Is this normal? I know the battery reduction issue is bigger at the beginning but...1.87% degradation already?

My other question is: does the range varies if the previous driving session has been more efficient? I mean if for example I've driven at 70mph will I get a higher guesstimate the next time I charge than if I've driven at 80mph with higher KWh consumption?

Thanks

 

[GeorgeSymonds]

Hi,

would like to share my situation as well.

Car is around 1 month old and I've done 2,500 miles, charging mostly at home with the 3-pin plug and maybe 6-7 SC sessions of 15-25 minutes.

I charge the car to 90% normally, but done 2 full charges as well. M3SR+

Once new, 90% battery meant 214 miles. Now, 90% means 210 miles. Is this normal? I know the battery reduction issue is bigger at the beginning but...1.87% degradation already?

My other question is: does the range varies if the previous driving session has been more efficient? I mean if for example I've driven at 70mph will I get a higher guesstimate the next time I charge than if I've driven at 80mph with higher KWh consumption?

Thanks

Answering the second part first, the range on the screen (not the energy consumption widget thing) uses a fixed rate so it doesn't care how you've been driving. Not sure why they do that as on the energyu consumption widget display it uses the average consumption over whatever you've set that display to show. Maybe it would give people heart attacks in winter as consumption can be really high at the start of a journey.

There are a few factors which can cause small changes, battery temp, rounding, cell balancing, 90% charge and then left with sentry mode on and it would drop a little compared to 90% and just finished charging etc so I wouldn't be worried over 4 miles at this time.

Some will say "show %" but you'd be ignorant of any changes like those you're seeing, just don't get hung up on a few miles here and there unless the trend is all one way and consistently dropping over time.

 

[VanillaAir_UK]

Once new, 90% battery meant 214 miles. Now, 90% means 210 miles. Is this normal? I know the battery reduction issue is bigger at the beginning but...1.87% degradation already?

tl;dr I don't think you have anything to worry about.

Not sure where you get your figures from, but its not really battery degradation even if TeslaFi calls it otherwise - it can go up as well as down. Its really an extrapolation of some figures that the battery management system (BMS) best guess at current battery state. As you cannot tell exactly what the battery level is on a lithium battery at any point in time, it really is a best guess that is more accurate at different states of charge. As a result, it is said that accuracy of BMS can be improved by occasionally letting the battery go low and high SOC. Another significant factor is that extrapolating on whole numbers does not give good accuracy. TeslaFi makes the assumption that a 'completed charge' is always to same fraction of a % so can be made to limit its values based upon completed charges. As a result of this, a 1% difference in battery charge level can make 2-3 mile difference when extrapolating numbers. So that could easily account for half your discrepancy.

Finally, loss of battery capacity is to be expected and normally flattens a bit from initial drop-off. Its the trend over a longer period of time or sudden significant drops (which may signify a failure) that are more important.

 

[Tracker]

Interesting Video on the subject

go to 1:24 to skip the boring stuff.