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Real degradation and how do you know by percentage display?

TomLee

Member
May 26, 2019
279
65
Vancouver
For whoever gets Tesla to acknowledge your battery degradation, were you able to charge your car to 100% or only to a certain percentage? Or anybody hasn’t been able to charge their car to 100%? The reason I’m asking is because a lot of ppl find us, who worried about battery degradation, annoying and suggest us to change to display % on the screen. I refuse to do that because ranges, however it fluctuate, at least tell me something. If percentage always shows 100% when charge to full, regardless of the degradation, it tells me no more than nothing. Is there a proven way to tell the real battery degradation or nobody knows? Thanks a lot!
 
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rhaekar

Member
Nov 9, 2017
455
380
San Diego
I can't imagine there is unless you charged to 100% and drove the entire way down to 0% and saw the kWh used. Even then you wouldn't have a baseline.

With the way the BMS works, it's all just an estimated calculation.
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
10,802
13,490
San Diego
were you able to charge your car to 100% or only to a certain percentage? Or anybody hasn’t been able to charge their car to 100%?

Most people are able to charge to 100%, even with degradation (or capacity loss). Sometimes a battery cannot charge to 100%, but then there is often actually a battery error (and then it gives a message saying battery cannot charge to 100% - you can search here for that error - it is associated with battery replacements).

Notification that battery cannot charge to 100%

If percentage always shows 100% when charge to full, regardless of the degradation, it tells me no more than nothing.

That's correct, it is not useful for judging degradation. You cannot see degradation (let's call it capacity loss, not degradation) easily when using % (energy) display. The Energy Screen Trip Planner DOES take into account your degradation (it converts to available kWh and then converts back to arrival % for display).

is there a proven way to tell the real battery degradation or nobody knows?

I recommend tracking your number of rated miles at a given set %. To the extent that changes, that means you have less available energy above 0 rated miles. (You can extrapolate to 100% if you wish but it is not really necessary to charge to 100% unless your BMS has issues.)

Each rated mile typically corresponds to a particular amount of energy (different for different types of Model 3).

That being said, it IS still an estimate - but it's actually typically a very accurate estimate - inaccuracies in the estimate can least to extremely bad results (stranded!), so Tesla tries very hard to properly estimate available energy and display it on the screen.

The display of rated miles is a measure of that available energy - Take the available rated miles and multiply by the Wh/rmi (discharge) constant to give you your energy available (above 0 rated miles) at any point in time, as measured on the trip meter.

Constants for each Model 3
 
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TomLee

Member
May 26, 2019
279
65
Vancouver
I can't imagine there is unless you charged to 100% and drove the entire way down to 0% and saw the kWh used. Even then you wouldn't have a baseline.

With the way the BMS works, it's all just an estimated calculation.

Understood. I think one can just drive precisely 219 Wh/mile from 100% to 0% in day 1 and later date to compare the loss, even though this is no very practical. your day 1 becomes your baseline.
 

ewoodrick

Well-Known Member
Apr 13, 2018
5,285
4,269
Buford, GA
Since you seem to want to believe that your battery has degraded, how close to 70% degradation do you believe you have? If it's not below 70%, Tesla isn't going to talk to you.

The number on the screen is an estimate based upon EPA numbers some calculations about the battery. It possibly seems as if V10 has changed some of the calculations, but then again, a number of updates have changed the numbers.

It has been shown and acknowledge that thing such as only charging your car to <90% can play tricks with the number and result in accurate results.

So, I believe that most everyone will agree:
  • The displayed name is based upon EPA numbers, which while reachable, doesn't represent most people's driving
  • The number is based upon a calculation that can get out of whack if the car is not charged above above 90% periodically
  • Battery degradation isn't necessarily calculable from the number, because the 100% number is variable (see above)
Your worry about battery degradation probably comes from range anxiety. Best way to get over range anxiety is to get out and drive the car. How many trips over 500 miles have you made. If less than 2, then worry about taking your next trip instead of battery.
 

TomLee

Member
May 26, 2019
279
65
Vancouver
Most people are able to charge to 100%, even with degradation (or capacity loss). Sometimes a battery cannot charge to 100%, but then there is often actually a battery error (and then it gives a message saying battery cannot charge to 100% - you can search here for that error - it is associated with battery replacements).

Notification that battery cannot charge to 100%



That's correct, it is not useful for judging degradation. You cannot see degradation (let's call it capacity loss, not degradation) easily when using % (energy) display. The Energy Screen Trip Planner DOES take into account your degradation (it converts to available kWh and then converts back to arrival % for display).



I recommend tracking your number of rated miles at a given set %. To the extent that changes, that means you have less available energy above 0 rated miles. (You can extrapolate to 100% if you wish but it is not really necessary to charge to 100% unless your BMS has issues.)

Each rated mile typically corresponds to a particular amount of energy (different for different types of Model 3).

That being said, it IS still an estimate - but it's actually typically a very accurate estimate - inaccuracies in the estimate can least to extremely bad results (stranded!), so Tesla tries very hard to properly estimate available energy and display it on the screen.

The display of rated miles is a measure of that available energy - Take the available rated miles and multiply by the Wh/rmi (discharge) constant to give you your energy available (above 0 rated miles) at any point in time, as measured on the trip meter.

Constants for each Model 3

Thanks for the advice, I am collecting numbers from daily ranges to charging sessions. I'm actually get annoyed by those ppl as more of those coming out as winter's coming. I'm not the type to just cover my eyes and pretend nothing happened. If I can't get it 100%, at least I know what's going on. Oh, well ...
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
10,802
13,490
San Diego
Battery degradation isn't necessarily calculable from the number, because the 100% number is variable (see above)

It's true that it is not "necessarily" calculable (for the reasons mentioned). However, in general, in the majority of situations, it is reasonable and quite accurate to use the available rated miles to assess how many kWh you have available.

I have lost a small amount of range (which I am not concerned about), and I have no doubt that the reduction in rated miles meant I had less available energy - by about 1.4kWh. The trip meter data, remaining range at my destination, etc. all support the rated range in miles as being a good predictor of available energy. Without the loss of available kWh, my North Rim to Vegas run would have been stress-free - as it was, I had to do a little drafting (arrived with 21 miles left - so I didn't HAVE to - but...margin....). Losing 2% matters...it means you have 2% less energy to get where you need to go! (Again, not that I am concerned.)
 
Last edited:

TomLee

Member
May 26, 2019
279
65
Vancouver
Since you seem to want to believe that your battery has degraded, how close to 70% degradation do you believe you have? If it's not below 70%, Tesla isn't going to talk to you.

The number on the screen is an estimate based upon EPA numbers some calculations about the battery. It possibly seems as if V10 has changed some of the calculations, but then again, a number of updates have changed the numbers.

It has been shown and acknowledge that thing such as only charging your car to <90% can play tricks with the number and result in accurate results.

So, I believe that most everyone will agree:
  • The displayed name is based upon EPA numbers, which while reachable, doesn't represent most people's driving
  • The number is based upon a calculation that can get out of whack if the car is not charged above above 90% periodically
  • Battery degradation isn't necessarily calculable from the number, because the 100% number is variable (see above)
Your worry about battery degradation probably comes from range anxiety. Best way to get over range anxiety is to get out and drive the car. How many trips over 500 miles have you made. If less than 2, then worry about taking your next trip instead of battery.

Thanks for your reply! I'm actually not that bad, about 9 miles lost @80% charge, so probably 3% - 4%. What I really worried is with a 240 miles rated car, I may not make it back from a 80-mile away ski resort without charging in the middle.
 

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