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Concerning battery degradation [question about warranty]

AAKEE

Active Member
Jan 8, 2021
1,106
1,641
Sweden
I This is 13.5% degradation over less than 2 year period.

No comment on the warranty stuff but for the degradation test.
You need to drive in about the same speed, using up the energy in about the same time.
Preferably the same road used at same speed or same average power.
I checked the cell voltages via ODBii reader and the cells are at around 3.16-3.17V under an equilibrium state (after ~1hr rest).

Checking an academic NCA OCV curve this is inline with approximately 3% SoC.
Tesla use 4.5% buffer below 0% SOC shown on the screen.
3% SOC on the screen should be about 7.5% true SOC.
You wont see the OVC in a OBD-tool, as the connectors isnt open when checking, and the battery do not get the OCV until the car falls asleep so you would like more than one hour parked.
When reading the voltage at low SOC, lights, AC and anything need to be shut of as it lowers the voltage with the load.

Anyway, looks that 3% on screen SOC was probable.

Subjective: I rarely ever charge to 100% (probably less than 15 times) and never let the vehicle sit at high SoC.
What is your regular charging level?
When do you charge? ”Coming home after work”?

Having the car at high SOC ( higher than about 60%) in warm climates will degrade the battery faster.
 
Beyond what's already been said, I'll just add that the degradation you (the OP) have experienced to date will probably be leveling out soon, if it hasn't already.

There's also a hint that your charging habits may not have been your friend. Notwithstanding how cool road trips in an EV are, and how delightful the Tesla Supercharger network is... DC Fast Charging is probably the harshest thing we can do to our EV battery packs. Your 36.8% suggests pretty frequent use.

Sorry your Tesla experience hasn't been happier. The good news is your car is new enough that you might be surprised how much you could get for it if you decide to go back to ICE.
 

MP3Mike

Well-Known Member
Feb 1, 2016
19,939
49,932
Oregon
All the time when the car is on? I thought it was only when it was needing a charge and not constantly on?
All the time the car is on. You don't want to be cycling your 12v battery constantly. (It only has enough energy to last maybe an hour with the car on, less depending on light/fan load.)

And actually there is a second smaller DC-DC converter that runs 24x7 to support the always on portion of the vehicle. (So that while it is sleeping it doesn't run the 12v battery down and have to wake the vehicle up to recharge the 12v battery.) Original Model S packs didn't have this feature, but it was added later to make the 12v batteries last longer and also have less vampire drain.
 
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All the time the car is on. You don't want to be cycling your 12v battery constantly. (It only has enough energy to last maybe an hour with the car on, less depending on light/fan load.)

And actually there is a second smaller DC-DC converter that runs 24x7 to support the always on portion of the vehicle. (So that while it is sleeping it doesn't run the 12v battery down and have to wake the vehicle up to recharge the 12v battery.) Original Model S packs didn't have this feature, but it was added later to make the 12v batteries last longer and also have less vampire drain.
Interesting! Wouldn't it be easier to not have a battery and just have both DC-DC converter powering everything?
 

MP3Mike

Well-Known Member
Feb 1, 2016
19,939
49,932
Oregon
Interesting! Wouldn't it be easier to not have a battery and just have both DC-DC converter powering everything?
I think they did that with one version of the Roadster and there were problems because of it. For example, when the HV battery reaches 0% and shut off, you then have no way to jump start the systems and recharge the HV battery.
 

AAKEE

Active Member
Jan 8, 2021
1,106
1,641
Sweden
Interesting! Wouldn't it be easier to not have a battery and just have both DC-DC converter powering everything?

As MP3Mike say, plus:
Then the HV Bat wouldnt get any ”sleep” and show the OCV etc.
During drives the HV Batt supply the 12V bat all the time, (maybe a switching power supply).
When the car is sleeping, the 12v stand forcthe energy itself.
 
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gaswalla

Model S,3,X.. CT with Austin delivery
Sep 23, 2012
3,992
4,942
San Diego
this is why it's best to get the largest battery possible... OP needed to charge fast and charge to higher SOC consistently - and that would have been mitigated by a larger battery.. it's not all about range per se. Charging to 80% in a battery with greater range results in less battery degradation than charging to 100% in a smaller battery (same net range)..
OP's experience is 'within spec' for the use the battery was put through, and the majority of degradation has already taken place - a trickle of degradation will continue to take place though
 
I'll double-down on what @AAKEE said, was the second test done in the exact same conditions: same road segment in the same direction, at the same speed with the same traffic, with the same wind, at the same temperature? Using the same type of tires at the same inflation? Without proper verification of all these factors, the test does not prove anything. A difference of 10% in consumption is highly probable if any of those conditions change. Even if the conditions are the same, there could be a variation. You cannot extract a precise degradation that way, at best it's an estimate.
 
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I'll double-down on what @AAKEE said, was the second test done in the exact same conditions: same road segment in the same direction, at the same speed with the same traffic, with the same wind, at the same temperature? Using the same type of tires at the same inflation? Without proper verification of all these factors, the test does not prove anything. A difference of 10% in consumption is highly probable if any of those conditions change. Even if the conditions are the same, there could be a variation. You cannot extract a precise degradation that way, at best it's an estimate.

Could not agree more.

Since the OP has access to his/her CanBus data, I'll just point out that the car collects and stores data that is much more useful for evaluating battery health than any over-the-road test could ever be.
 
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