~3% Degradation in 3 months?

KFORE

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#1
I may be reading too much into the est. range indicator, but I always charge to exactly 71% every night (set via the API) and recently my range after completing charging has been dropping. When I first got the car 3 months ago, 71% gave me 228 miles remaining nearly every time. Was usually 226-228. Now, it has dropped to 218-220 for the last week.

I almost always charge to 71%, never super charge, and have only had the car for ~3 months. My lifetime wH/mile is 231. Is this something to keep an eye on or is the est. range constantly going to float like this?

I also recently charged to 100% right before a long trip and only got 305 miles.

I have a LR RWD Pearl White TM3, VIN 23XXX, FW 2018.32.2.
 
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mdfraz

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#2
I have had the car just over 5 weeks and I charge it to 90% at home every night. It's usually 278-279, but it's been as low as 275 on a semi regular basis. I'm not too worried about it typically, but I lost ten miles (from 279 to 269) in about a 6 hour period on two occasions overnight, all while plugged in. I don't set the car to charge at a certain time, so that shouldn't be the cause. Losing any miles while plugged in has me concerned, but especially when it's 10 miles, in my garage, overnight, while plugged in.

I have charged to 100% just once, and I also got 305 miles instead of 310. Not horribly concerned about it, but I'm curious about how these things might fluctuate going forward.
 

KFORE

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#3
Ah, thanks for the info. Makes me feel a bit better. I don't have a lot of vampire drain, but everything else seems in line with your experience.
 

MelindaV

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#4
the best summary of what Lithium batteries do is covered in this two part interview on The Tesla Show podcast with Bernard Kim, a PhD specializing in batteries.
Batteries Part 1
Batteries Part 2
essentially, the batteries will naturally lose a bit of capacity as part of its initial conditioning, then that slows down significantly (to simplify it way down, it essentially develops a 'plaque'; keeping the battery 100% or 0% charged and sitting without being used will also cause 'plaque', which is why you don't want to do that).
 

garsh

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#5
Current battery degradation studies on Teslas have concentrated on the Model S, just because they've been around long enough that we have plenty of data. But it should be applicable to the 3 as well.

There tends to be a steeper drop in battery capacity initially, which then levels out.
How many miles do you have on your car, @KFORE?
(p.s. - shouldn't the x-axis be called "meterage"? ;))
(p.p.s. - note the y-axis doesn't start at 0. Click through to the reference article for a version of the graph where it starts at 0)



Reference:
Tesla battery data shows path to over 500,000 miles on a single pack
 

KarenRei

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#6
I may be reading too much into the est. range indicator, but I always charge to exactly 71% every night (set via the API) and recently my range after completing charging has been dropping. When I first got the car 3 months ago, 71% gave me 228 miles remaining nearly every time. Was usually 226-228. Now, it has dropped to 218-220 for the last week.

I almost always charge to 71%, never super charge, and have only had the car for ~3 months. My lifetime wH/mile is 231. Is this something to keep an eye on or is the est. range constantly going to float like this?

I also recently charged to 100% right before a long trip and only got 305 miles.

I have a LR RWD Pearl White TM3, VIN 23XXX, FW 2018.32.2.
Degradation is fastest in the first two years. Of those, fastest in the first year. Of those, fastest in the first six months. Of those, fastest in the first three months.... (etc)

Basically, as you charge and discharge a li-ion battery, you're making the cathode and anode side alternately swell and contract (li-ion batteries work through intercalation - the embedding of ions into pores or inter-layer space in a solid matrix). The most vulnerable microstructures rupture and become inactive mass first, while the more durable microstructures persist. Basically, you're weeding out the weak portions of your battery electrodes ;) Also over time reactions between the electrodes and electrolyte start to form a buildup on the anode, but the presence of the deposit slows down the formation of further deposits.
 
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BigBri

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#7
It might not persist as the car is doing those calculations based on a ton of factors. Perhaps it's been windier and your WH/M has gone up more recently or the temperature has been hotter etc. Lots of factors to consider. I'd not worry, sounds like you're treating the battery well.
 

P=VI

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#8
I've seen ~5% (15 miles) degradation over 4 months / 4000 miles, from a max of 310 miles down to 295 miles.
My daily charge limit is 75% and I've probably only charged to full 3 or 4 times.

It does seem strange that there was a sudden dropoff, rather than a linear degradation.

img_1235-jpg.14189
 

KarenRei

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#9
I've seen ~5% (15 miles) degradation over 4 months / 4000 miles, from a max of 310 miles down to 295 miles.
My daily charge limit is 75% and I've probably only charged to full 3 or 4 times.

It does seem strange that there was a sudden dropoff, rather than a linear degradation.

View attachment 14189
Could be a loss of a cell. There's a reason that you have so many of them :)

Loss of a cell in large-format prismatic-cell-based battery packs is less likely, but if it happens, you're in serious trouble.
 

TirianW

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#10
One other thing to consider is that we don't know how much capacity the BMS actually thinks the battery has; all we have to work with is the estimated mileage and charge percentage as reported by the car's UI. For example, a minor tweak to the algorithms in a firmware update could cause the range reported to change without any actual capacity change of the battery. So while I am not saying that the estimated range is completely useless for tracking battery health, I would be very hesitant to base any predictions about battery health on an algorithm that we don't even know all the inputs to. For example, there could be a component that estimates average temperature based on location and date to correct the mileage for HVAC load. We know that in summer and winter more energy is spent conditioning the cabin than in spring and fall (for most temperate latitudes, in most years). Because Tesla does not document how their range is calculated, we can only guess what parameters may be included in that calculation. Clearly energy stored in the battery is the primary component of that calculation, but driving history and temperature are also common in the industry (although not necessarily for Tesla). Additionally, the Model 3 is a new platform for them and the calculation may not be as simplistic as the one in the S/X - they now have a lot of collected data from their S/X fleet around the world and may now be starting to take additional factors into consideration to provide a more accurate number for the Model 3. Without access to the numbers provided by the BMS, I would be hesitant to make any analysis of the battery system.


* Note: all this assumes that the range is based on full = 100% battery capacity and 0 miles = 0% remaining. We know from previous Tesla vehicles that the batteries can be oversized with a software limit to prevent the physical pack from charging to 100% or discharging to 0%. This significantly increases the lifespan of the pack and can hide some age / cycle count related degradation - just like computer SSD manufacturers put more flash memory into their drives than is actually exposed to the operating system (or like HDD manufacturers did with spare physical sectors and the LBA remap table). Given that we don't know what charge state of the physical pack is represented by X% charged on the UI and we don't know what available energy in the pack is represented by X miles of range, it is really challenging to make any predictions about what the BMS is actually doing based on reported range at a reported charge state.
 

fsKotte

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#11
I've seen ~5% (15 miles) degradation over 4 months / 4000 miles, from a max of 310 miles down to 295 miles.
My daily charge limit is 75% and I've probably only charged to full 3 or 4 times.

It does seem strange that there was a sudden dropoff, rather than a linear degradation.

View attachment 14189
I’m in a similar but not quite exactly the same situation - 4k miles, 3.5 months old car, almost always charge to 75% (but did 100% three or so times for longer weekend trips), and as of today my range is at 302 miles (227mi when charged to 75% = 302 miles @ 100%). So that’s 2.6% degradation.

A little worrisome.
 

Technical48

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#13
I may be reading too much into the est. range indicator, but I always charge to exactly 71% every night (set via the API) and recently my range after completing charging has been dropping. When I first got the car 3 months ago, 71% gave me 228 miles remaining nearly every time. Was usually 226-228. Now, it has dropped to 218-220 for the last week.

I almost always charge to 71%, never super charge, and have only had the car for ~3 months. My lifetime wH/mile is 231. Is this something to keep an eye on or is the est. range constantly going to float like this?

I also recently charged to 100% right before a long trip and only got 305 miles.

I have a LR RWD Pearl White TM3, VIN 23XXX, FW 2018.32.2.
I my experience the range estimate for a given SOC can drift downward. Once I allowed the battery to discharge below 10% and the range estimate went back to "normal" on next charge cycle. And by normal I mean that 100% is 310 miles and the range estimate scales linearly between 0-100%.
 

Dogwhistle

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#14
I charge to 81% every night, which consistently gets me 251-252 miles. The full charge equivalent of 310-312. 3 months and 7000 miles on it.
 

Beagle

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#15
3.5 months old. 3,500 miles. The car came with what I guess is factory preset charge to 90%, 280 miles. We did one 100% charge after about 1,500 miles, and then changed to 80% charge that came to 250 miles. We charge anywhere from one to three times a week, and rarely indicate <100 miles. Our present indicated 80% charge is 239-240.
 

tivoboy

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#16
I'm going to add something to this thread, and pardon me it is going to sound TOTALLY crazy.

originally, I was getting 310-311 miles on full charge. Seemed normal. After a few months, I was only getting up to 307/8 on full charge. Okay, charging can be impacted, different charges rates x frequency etc.

What happened in the interim though, was I had purposely LOWERED my tire psi to cold 41 (at speed in temps 43/44), to see if cabin noise would be reduced (it wasn't really incidentally).

Last weekend, for a longer road trip, I moved tire pst back up to cold 44 (at speed in temps 47) and I put the car on the charger.

It showed 310. I did the road trip, using about 60% of the battery and then did another full charge. It showed 311.

could it POSSIBLY be, that in the represented available remaining miles, that the cars calculator IS taking some other variables into consideration when displaying a remaining miles calculation?

The ONLY thing that has changed in the interim is the changes to psi. Driving and charging sources have remained pretty much the same. (combo of 14-50 24A, 30A public and 10% Sc).
 

Rourke

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#17
I just found this thread after finally hitting on the right search terms. I've seen the exact same change in my estimated range post-charge on the same firmware version and with nearly identical age/mileage stats. My suspicion was that it was a new way of calculating in 2018.32.2 but the drop didn't coincide exactly with the update of my car. I have never charged to 100%, have only used a Supercharger once for about 10 minutes on my way to a meeting just to try it out, and charge daily to 80% on a NEMA 14-50. I was seeing around 248 miles remaining after charging then suddenly it dropped to 236 a few weeks ago and it's been holding there ever since. I'm averaging 230 wH/mi life-to-date and recently logged a 40-mile round-trip at 214 wH/mi with no return to my previous 248 mile range estimate.

Thanks @tivoboy for the suggestion. I did get an alert this morning that my tires are at 36-37psi so I'll re-fill them this evening and see if that fixes the range. I'll post an update tomorrow.
 

Jay79

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#18
I'm going to add something to this thread, and pardon me it is going to sound TOTALLY crazy.

originally, I was getting 310-311 miles on full charge. Seemed normal. After a few months, I was only getting up to 307/8 on full charge. Okay, charging can be impacted, different charges rates x frequency etc.

What happened in the interim though, was I had purposely LOWERED my tire psi to cold 41 (at speed in temps 43/44), to see if cabin noise would be reduced (it wasn't really incidentally).

Last weekend, for a longer road trip, I moved tire pst back up to cold 44 (at speed in temps 47) and I put the car on the charger.

It showed 310. I did the road trip, using about 60% of the battery and then did another full charge. It showed 311.

could it POSSIBLY be, that in the represented available remaining miles, that the cars calculator IS taking some other variables into consideration when displaying a remaining miles calculation?

The ONLY thing that has changed in the interim is the changes to psi. Driving and charging sources have remained pretty much the same. (combo of 14-50 24A, 30A public and 10% Sc).
Pretty smart, this is a very real possibility. PSI is a huge factor in rage and the car can absolutely use this as part of the calculation for range if Tesla wanted it to. It ceartainly would make it far more accurate in range estimation
 

GregRF

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#20
Pretty smart, this is a very real possibility. PSI is a huge factor in rage and the car can absolutely use this as part of the calculation for range if Tesla wanted it to. It ceartainly would make it far more accurate in range estimation
There is a similar thread over on TMC. And as I post there, as far as we know "Rated Range" is just a static equation that doesn't take anything into affect except the BMS's reported kWh.

You can check out this thread by @wk057 . Relevant excerpt:

"These are the exact numbers pulled from the Tesla firmware. Rated miles are static Wh/mi. They do not change with driving style or anything else besides the configuration of the car as noted above. The car simply takes the estimated usable energy remaining as reported by the BMS, divides by the appropriate static number above, and displays the value."

(This is from a thread about X and S but I see no reason why it wouldn't be the same in the 3)