Used Tesla from Dealer - Battery Concerns Valid?

[Jrm3]

Hey TMC,

I have had a Model 3 SR+ since 2019 that I bought new. I'm now looking at trading it in for a model y for the extra cargo space. I've considered possibly buying used from a place like CarMax (although it may or may not make sense with the current tax credit).

I'm aware of general battery degradation expectations and I expect that anything used will have a small amount of degradation (generally that year 1 degradation that is most substantial). My question is whether folks have heard or had experiences with the degradation seen on used Teslas specifically from 3rd party dealers.

My concern is partially from not being able to speak to the previous owner about charging habits, but also a concern that the dealer could have just let the car sit with almost no charge or 100% charge for an extended period of time and thus cause additional degradation. Does anyone have experience or knowledge as to whether or not this is a valid concern?

 

[johnny_cakes]

I recently purchased a used 2019 Model 3 and was concerned about the same thing. I used the technique outlined here to estimate the battery's capacity.

 

[AAKEE]

My concern is partially from not being able to speak to the previous owner about charging habits,

The technique described in that link will tell you what capacity the BMS estimates at that moment that the battery have.

BMS estimation can be wrong, both up and down. Its probably about correct but can be off by a fair number.
The ”True within 1kWh” stated in the link is not always true.

but also a concern that the dealer could have just let the car sit with almost no charge or 100% charge for an extended period of time and thus cause additional degradation.

If the car is left at 100% for an extended period, this is not even close to as bad as the forums ”myths” states.
As long as the ambient temperature is normal, lets say not higher than 25-30C/ 75-85F the difference in degradation is between none and very small compared to a SOC of 80-90%.

That said, I never leave my car with high SOC, and high for me is >55%.

If the dealer did leave the car with low SOC, thats a good thing. As long as the car did not shut down due to well below 0% on the screen, the lower the better. I often leave my car with low SOC.

The chart below show the calendar aging of Panasonic cells with the same NCA chemistry as Tesla use.
For the blue 25C line we can se a marginal increase in degradation above 90%. Actually, it is hard to see as the difference is very small between 90% and 100%.

We can also see that the lower the SOC, the lower the calendar aging. This is valid down to 0% true SOC which is below the 0% on-screen-SOC due to the 4.5% buffer Tesla use.

If the car is parked with low SOC, this is good.

In the end, most people have their cars charged to 70-90% over the nights, the big part of the initial degradation has already happened due to this.
There will be no big difference if it is left at 80,90 or 100% at the dealer waiting for you.

(Parked for long times at high SOC increase the calendar aging compared to normal use as when the car is used the SOC normally is lower during the day. But in the store, the difference between 80-100% is not high).