2019 M3P-, Took delivery in early august.
Lifetime wh/mi: ~280
Charging habits: Charge to 70 in summer, 75-80 in winter. plugged in every night inside a garage, Garage is at 80F in summer, ~50F in winter. Charge to 90% when visiting family and trickle charging on 110V, but it takes awhile.
a few bigger road trips, approx 10-20 supercharges.
Never charged to 100%, only charged to 97% once to try to enable balancing.
View attachment 503519
Looks extremely similar to mine - started dropping at about 6k miles, and now sits at 300rmi. I also had the plateau at around 304rmi! You can see the evidence of my theory here. As we know, batteries degrade fastest when they are new. But there is no evidence of this in this plot - it is totally flat for the first 5000 miles! You can see when winter and summer are in your plot - there is more error on TeslaFi's estimates when the SoC is set lower (due to SoC lack of precision). So more fuzz in the summer time. Right now it is nice and tight.
The EPA data (which shows the pack should have about 78-79kWh at 1000 miles) and the constant (which with 310 rated miles would project to 76kWh) suggests that actually Tesla starts with "turgid" rated miles which contain more energy (though this is not indicated on the charging screen, it is only visible through the CAN bus or careful observation of the trip meter, or by making extremely careful observation of wall energy added during charging sessions when the vehicle is new relative to miles added, and comparing to charging sessions when degradation becomes visible), and then they slim down (but do not reduce in number), and then finally they start to disappear when your capacity drops below 76kWh (where 245Wh/rmi becomes the correct endpoint value).
For you, this endpoint (where miles actually started disappearing, even though you already had at least 2% degradation) happened at around 5000 miles.
Another way to look at this: You actually started at 318-322 rated miles (the reason it's so high is because Tesla made the constant too low...more on that below...), but it was "hidden" by the "inflated" rated miles (note: it is NOT a cap where your miles stay pinned at 310 miles when you start driving - each mile is inflated so they will immediately begin ticking off, they just tick off more slowly when the car is new!).
That's my theory, and I'm sticking to it. It fits all the data/observations we have:
1) We know batteries degrade fastest when new but this is not apparent in your plot. Something is amiss. (This is what happens to almost all the old 2018/2019 LR vehicles.)
2) From Bjorn videos, we know that initially on new vehicles, the trip meter shows more energy per rated mile than later in a car's life.
3) The CAN bus data shows over 78kWh of capacity on new vehicles. This doesn't fit with what we know about the 310rmi*245Wh/rmi (76kWh), so implies that that "245Wh/rmi" must not be the case *initially* at least. (It's worth noting that the "correct" value of this constant in 2018/2019 should have been 255Wh/rmi (so that 255Wh/rmi*310rmi = 79kWh).
4) We know rated miles start ticking down immediately as you drive even when starting at 100%, so we know it's not just energy "above" 310 - if it were, it would stay pinned at 310 for quite some time when the car is new.
Anyway, what this means is that you're at about 6% degradation (299/318) at this point (not 3-4%). And that's what the CAN bus would tell you (it would say you have ~73kWh and it would also have told you you started at ~78-79kWh).
Based on what we're seeing on the 2020 Peformance, it looks like Tesla may have modified this strategy and now will just show nearly all your miles to start with (in addition to getting efficiency improvements on the AWD). Now the constant will be 247Wh/rmi, but that's actually the correct value. It doesn't look like they'll be doing quite as much of this "deflation" of the rated miles over time. (I say this because 264Wh/rmi*294rmi is 77.6kWh and the EPA test for 20" gave 79kWh, so only 1.4kWh hidden right now - exact amount hidden would depend on exactly where your pack starts.)
The confirmation of this theory will be the TeslaFi results from brand new Performance 2020 vehicles over time - will they start showing degradation a bit sooner?
I think they may adjust the constant down to 260Wh/rmi later so that 299 ends up the max. So that means less inflation (260Wh/rmi vs. the correct 264Wh/rmi, compared to 245Wh/rmi vs. the correct 255Wh/rmi before). It may be that they have better control over initial pack capacity now, so they can tighten things up a bit, and still make everyone "happy" to start with the "full" number of miles. (I think this may be a motivating factor for this entire treatment - they want everyone to start out with the same number of rated miles, even if their initial pack energy may vary by up to ~2kWh - that variable capacity (presumably some tolerance is allowed by the EPA) is hidden at the time of sale.)
This may also largely explain why people see such different "plateaus" in their miles after a year. If the initial starting point differs by 2-3kWh, that would mean that once that start point is "revealed," we should expect to see 8-12 miles difference in the rated miles people get at 100% after basically equal degradation has occurred. For example, someone starting with 76kWh would start at 310, and someone with 79kWh would also start at 310. After 6% degradation, they'd be at 71.5kWh and 74.3kWh, or 292rmi and 303rmi. Same % degradation, but that startpoint difference is now evident.
