Is my battery degrading?

[Ctein]

Dear Folks,

My 2020 TeslaX has about 20K miles on it now, probably more than half my charging being Supercharging (I do a lot of distance driving), the rest 120V trickle-charging at home. I've been suspicious that I'm losing battery capacity, so I ran the following check on my current vacation trip. Last night, I Supercharged to 97%. When I took off this morning I started with 93% — about the amount of loss I'd expect for overnight with Sentry mode on, so nothing odd there. But... I nearly ran out of charge getting back to the motel — I was down to 2%! But the Tesla's tripmeter reported only 76KWh consumed! That's consistent with what it reported as my average mileage and the number of miles driven today. Way low for a car that's supposed to have a 100 KW battery! The car's trip data for the day computes out to barely 85 KWh battery capacity.

I can't believe my battery has degraded by 15% since I bought the car two years ago. Mostly I keep it between 10% and 90% charge, as everyone recommends. In fact, rarely do I drop much below 20%.

What gives! Suggestions? Is there any way I can investigate this further?

If I can confirm a 15% loss in 2 years and 20K miles, do folks think I'm likely to get any satisfaction complaining to Tesla Service?

Thanks!

Ctein

 

[Tam]

...15% loss...

You can ask Tesla but I doubt it will take in your issue until it's more than 20% loss in 8 year new car warranty or 125,000 miles whichever first.

 

[ucmndd]

If I can confirm a 15% loss in 2 years and 20K miles, do folks think I'm likely to get any satisfaction complaining to Tesla Service?

No. They don’t care, won’t care. It will be a complete waste of your time.

You can ask Tesla but I doubt it will take in your issue until it's more than 20% loss in 8 year new car warranty or 125,000 miles whichever first.

You mean 30%.

 

[Ctein]

No. They don’t care, won’t care. It will be a complete waste of your time.


You mean 30%.

No. They don’t care, won’t care. It will be a complete waste of your time.


You mean 30%.

Well, for my own piece of mind, are there other diagnostics or calibrations I could run to determine whether or not I'm really suffering battery degradation?

 

[Harvey Danger]

Before you get too outraged, the car never had 100 kwh of capacity even when it was new. It's a nice round number but that's not really how it works (and your feeling of getting not getting what you paid for is exactly why they don't put numbers on the back of the car anymore).

If you didn't measure it when it was new, you don't really know how much it's degraded.

if you really want to make an estimate of degradation, this might be the one time it's helpful to display the state of charge in "rated miles" instead of percent.

Charge it to full. How many rated miles does it display? Compare that to the number tesla advertised as the rated range when it was new.

 

[jjrandorin]

Well, for my own piece of mind, are there other diagnostics or calibrations I could run to determine whether or not I'm really suffering battery degradation?

In the model 3 subforum, we have a sticky thread that explains how someone can calculate the capacity of their battery using the information on the screen.

I dont have an X so I dont know if the screens are exactly the same, but you should be able to find the info and calculate it yourself.

The car does not show energy used from anything other than driving, so heating isnt shown in the consumption number you saw, unless the model X is different.

Here is the thread with the information I mentioned:

Calculating Your Battery's Estimated Capacity Using the Car's Energy Screen

Re posting here and making this a sticky post so it doesnt get lost. @AlanSubie4Life originally posted: =========================================== (originally posted by @AlanSubie4Life. Original thread this appeared in can be found here: ( 2021 model Y scan my Tesla battery size)...

teslamotorsclub.com

 

[Ctein]

Before you get too outraged, the car never had 100 kwh of capacity even when it was new. It's a nice round number but that's not really how it works (and your feeling of getting not getting what you paid for is exactly why they don't put numbers on the back of the car anymore).

If you didn't measure it when it was new, you don't really know how much it's degraded.

if you really want to make an estimate of degradation, this might be the one time it's helpful to display the state of charge in "rated miles" instead of percent.

Charge it to full. How many rated miles does it display? Compare that to the number tesla advertised as the rated range when it was new.

Hey, Harvey!

Well, more like perturbed at almost running out of charge than outraged. Heh. Wouldn't have been close if I weren't driving in unfamiliar territory (Death Valley). I *do* know better. Normally. (ahem)

Just now, looked at the charge limit settings on my phone app: it says that a 100% charge would correspond to 336 miles. When it was brand new, it said 350 miles. If that's a valid indicator — is it? — then that'd be only a 4% degradation, which is hardly unusual.

Tomorrow night I'm going to Supercharge it to near 100%, in preparation for the long drive home. I'll set the display to show me what miles it thinks I can drive. Haven't paid attention to those "rated miles, since they're pretty useless IRL, but this'd be the exception...

Thanks for the suggestion! I'll report back.

pax / Ctein

 

[Ctein]

In the model 3 subforum, we have a sticky thread that explains how someone can calculate the capacity of their battery using the information on the screen.

I dont have an X so I dont know if the screens are exactly the same, but you should be able to find the info and calculate it yourself.

The car does not show energy used from anything other than driving, so heating isnt shown in the consumption number you saw, unless the model X is different.

Here is the thread with the information I mentioned:

Calculating Your Battery's Estimated Capacity Using the Car's Energy Screen

Re posting here and making this a sticky post so it doesnt get lost. @AlanSubie4Life originally posted: =========================================== (originally posted by @AlanSubie4Life. Original thread this appeared in can be found here: ( 2021 model Y scan my Tesla battery size)...

teslamotorsclub.com

Dear JJ,

Thank you for the link! I can totally give that a go-- the Model X screen is a bit different, but not in any ways that matter. I get fundamentally the same energy consumption info displayed.

FWIW, as an aside, I don't think my BMS is miscalibrated. At home, Sentry mode is always off and most nights I don't need to put the car on the 120V, so it regularly gets to "sleep" with anywhere from 20% to 90+% of charge.

pax / Ctein

 

[Rocky_H]

The car does not show energy used from anything other than driving, so heating isnt shown in the consumption number you saw, unless the model X is different.

No, that's not it. I think you're just mixing up the detail a bit. Those counters will include heating and ALL other kinds of energy use, but the thing that trips people up is not realizing that they are only operating while the car is in Drive or Reverse gear. So there can be a significant amount of usage in those in between times if the car is in Park or is turned off for longer periods of time in between driving.

But... I nearly ran out of charge getting back to the motel — I was down to 2%! But the Tesla's tripmeter reported only 76KWh consumed!

So that may be some of what @Ctein was seeing. You never gave any details about what this day consisted of. Was it going around to several places during the day with some starts and stops and parking for a while before heading back to your hotel? That time while parked won't be counted in those cumulative trip counters.

 

[rjpjnk]

Charge it to full. How many rated miles does it display? Compare that to the number tesla advertised as the rated range when it was new.

The problem with this approach is it depends on the car’s estimate of miles per kWh, which changes all the time due to driving style and temperature.

All that is really necessary to access degradation is to estimate the battery’s current capacity. Adding the miles/kWh factor just introduces inaccuracy.

The method posted above from the M3 thread is a better approach.

 

[Rocky_H]

The problem with this approach is it depends on the car’s estimate of miles per kWh, which changes all the time due to driving style

No, that is false. That is called a "Guess-O-Meter". That is what all OTHER car makers do with their electric cars. Tesla does not do that. It doesn't shift and tune based on ever-charging efficiency levels, based on who has been driving recently and how they have been driving. It's a measurement of the amount of energy, converted by a FIXED efficiency constant for that model of car.

and temperature.

That is slightly a thing, but that's because shifting temperature really does affect how much energy the car will be able to get out of the battery. So the car shifts that a little bit in its measurement of the amount of energy.

 

[rjpjnk]

You’re right. I just read that same detail in another thread that quoted the owners manual saying basically that the miles remaining is based on a fixed number and not driving style. I would have come back to change my post but you beat me to it.

So based on this information it appears the miles remaining estimate is merely a constant times the estimated usable capacity remaining. Is this correct?

 

[Harvey Danger]

Short answer, yes.

 

[Soey22]

I believe I’ve also lost 4% but my charging is 80% at home. I have a July 2019 P100D and I’m at 35k Miles. Brand new rated 305 and now it’s 294. I go constantly from 90% - 40% or 80 - 30%. Photo is in Km, but I’ve posted here in miles to simplify.

 

[rjpjnk]

…It's a measurement of the amount of energy, converted by a FIXED efficiency constant for that model of car.

Given that this is the case, then it seems if I knew the value of this constant I could easily convert my battery icon quantity from miles remaining to kWh remaining by simple division.

Any idea what this constant might be for a 2021 MYLR?

 

[Harvey Danger]

To determine your car's constant, go to a supercharger. Switch to percent, not miles (ie 'energy' not 'distance' in the display control panel). During the charge, two numbers will be displayed side by side, kilowatts and miles per hour. Their ratio is your charging constant. This ratio may appear to jump around a bit during the charging session but the variation is only due to rounding: it is always the same constant that relates the two displayed numbers at any given instant. If you write down five or 10 pairs of these readings as the charging speed changes and keep doing the same calculation on each pair pretty soon you'll converge on the actual number for your vehicle.

(At least for its current firmware, that is; occasionally over the life cycle of a model, Tesla will send an update that might modify this constant once or twice, but after the model has been in the wild for a year or so it tends to not change after that.)

Just to spell out the math, if you divide kilowatts by miles/hr you get a number like 0.247 kwh/mi. Multiply this by 1000 to get your constant in Wh/mi.

 

[Richbot]

OP, I also have an LR+, but don't supercharge much, maybe 10% of my total miles.

While driving, the mental math and the car's math seem pretty close to 1% = 1kwh on my H battery car with a little over 19,000 miles on it. How far that 1% carries you is obviously going to be variable. It's been hovering around 363-364 displayed miles at 100% recently, but after this latest trip is back to 370 again, so ?

I think we need a few critical numbers from OP. How long was lunch, how many beers were had at lunch, how long did you sleep in the car on the way back to the hotel, dash wh/mi readout, that kind of thing

My car's constant is 270 wh/mi , btw. So the car still "thinks" it has between 98 and and 99.9kwh of total capacity depending on the day

 

[rjpjnk]

To determine your car's constant, go to a supercharger. Switch to percent, not miles (ie 'energy' not 'distance' in the display control panel). During the charge, two numbers will be displayed side by side, kilowatts and miles per hour. Their ratio is your charging constant. This ratio may appear to jump around a bit during the charging session but the variation is only due to rounding: it is always the same constant that relates the two displayed numbers at any given instant. If you write down five or 10 pairs of these readings as the charging speed changes and keep doing the same calculation on each pair pretty soon you'll converge on the actual number for your vehicle.

(At least for its current firmware, that is; occasionally over the life cycle of a model, Tesla will send an update that might modify this constant once or twice, but after the model has been in the wild for a year or so it tends to not change after that.)

Just to spell out the math, if you divide kilowatts by miles/hr you get a number like 0.247 kwh/mi. Multiply this by 1000 to get your constant in Wh/mi.

Very clever. Thanks.

Just to be perfectly clear, do you agree that this constant is a property of the model and not the individual car? I only ask because you said “to determine your car’s constant”, but I believe you meant the 2022 Model Y constant.

 

[Harvey Danger]

The constant is hardcoded in the firmware. The firmware is determined by your car's individual hardware configuration.

(Which gives you an idea of the software development hell tesla is in as the number of unique hardware configs proliferates over time)

As a practical matter, yes, all 2021 MY LR's *running the current firmware* will have the same constant. Your specific VIN was probably not a unicorn whose battery pack or drive units or whatever differed from the cars before and after it on the assembly line.

 

[jjrandorin]

Very clever. Thanks.

Just to be perfectly clear, do you agree that this constant is a property of the model and not the individual car? I only ask because you said “to determine your car’s constant”, but I believe you meant the 2022 Model Y constant.

This is the model X subforum so "your cars" constant would be "your models" constant. The constant on the model x is not going to be the same as your model Y.