Sudden 1.5% drops in energy

[lanbo]

• New car. Less than a year with very little mileage (15,000 kms). When new I charged up to 90% and showed 450kms.
• The car has only been charged 5 or 6 times in a supercharger. It has always been within the % ranges recommended by Tesla to avoid premature degradation except for calibration purposes following Tesla's advice.
• The degradation of a battery (in general) is a progressive process.
• On the other hand, in the case of my car, it has received sudden energy estimate drops, coinciding with software updates.
• Specifically I first observed a drop to 484kms that did not worry me excessively. I'm not sure how the car got to that point (3.2%). May have been in two steps, progressively or in one step. At that moment, I was not really concerned about loss.
• Since then it has received 2 drops of exactly 1.5%. The first up to 4.7% when the car had less than 10,000kms (6 months). I could clearly notice it. That was the first time I contacted Tesla and they told me about possible errors in the car's BMS estimation system. They recommended some guidelines to correct a supposed deviation in the BMS that did not help. I decided not to worry excessively about that.
• Recently the car has received a new drop again of exactly 1.5%. It has also been a sudden drop. Now the loss of available energy is 6.2%. I have received new recommendations to recover the available energy that have not worked either.
• It looks like the BMS in a car *may* display less available capacity because of a set of different reasons:
  • real degradation
  • BMS bias
  • question: capacity cap?

Could Tesla be lowering by software the available capacity of some batteries? Why?

 

[AlanSubie4Life]

Yeah, it does seem to come in discrete chunks.

My guess is the CAC (calculated Ah capacity) estimation result and adjustment is quantized, since it does not have to be perfect, but I will have to see if there is information to read about on this.

You’ll find your car takes a bit less time to charge now, due to reduced energy needing to be added.

My theory is that you don’t see loss of capacity initially because the energy content of the rated miles is inflated when capacity exceeds the “max” threshold for the vehicle (76kWh in your case). Just a good way of concealing initial degradation, making all batteries appear the “same” initially, in spite of manufacturing variance, etc.

 

[lanbo]

making all batteries appear the “same” initially, in spite of manufacturing variance, etc.

That would be no good, either. Could they also be selling batteries that they already know that are below the advertised range?

That would lead to a lot of questions. What is an acceptable tolerance? Guarantee covers more than 30% in 8 years. That leaves a lot of margin for what they could accept as initial tolerance. What would they consider reasonable? What will consumers accept as reasonable? Is it ok to hide a well-known variance and only show it little by little so that the user does not give back the car in the 15 days trial period? Does it depend on the country and different laws? Can they cherry-pick which batteries go to different users? Could they give the best batteries to their largest affiliates or set them in cars used by reviewers for example? I could continue...

I still believe there's a possibility they are limiting some batteries because they discovered something about them. The exact 1.5% sudden drops coming after software updates are really strange.