Why does my car say charge complete if it's not all the way to the line

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bottomsup

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#1
the last few days it was topping off at 217 but i noticed today 212 and if you look closely the the green is not touching the line. Any ideas?
 

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Bokonon

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#2
the last few days it was topping off at 217 but i noticed today 212 and if you look closely the the green is not touching the line. Any ideas?
Did it show 212 right after charging had completed, or did some time pass between the charge completing and the car showing 212? Wondering whether your car may have slipped back down to 212 (~68%) due to vampire drain after charging had completed.

There is also a small amount of variability to the exact number of rated miles the car will report when charging stops, since the battery's calculated state of charge is only updated a few times per minute. My charge usually completes with rated miles anywhere within a 2-mile range.

Others have reported that their rated miles for the same charge % seem to change from one firmware update to another (though this has not been the case for me). And, of course, it's possible that your battery has experienced some degradation since your last charge... But that shouldn't have caused charging to stop short of the target line.

In general, though, I would wait to conclude that something has changed until you see a series of 70% charges that all result in fewer rated miles than you had previously.
 

Bokonon

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#4
I looked at it about 7 hours after it completed charging
Got it. Then what you're describing isn't that unusual, IMHO.

My typical case is the charge completes around midnight, and by the time I leave for work in the morning, I've lost a mile, maybe two. But there have definitely been a couple of instances where I've lost 4 or 5 miles overnight post-charge as well. If I had woken up and tapped the "charge completed" notification on my phone in these cases, I would have seen exactly what you saw.
 

Bernard

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#5
I looked at it about 7 hours after it completed charging
Range is a tricky measure. The car starts by measuring it from a default setting for efficiency (around 240Wh/mi), but of course no two of us drive the same way, with the same loads, on the same roads, so the car constantly updates its measure of efficiency, so it can give you better information on remaining range. (Efficiency is very sensitive to average speed and style of driving, perhaps even more so than in an ICE car.)

So one explanation is simply that, when you set the charging level in miles of range, the car translates that to a value of total energy in the battery using the current efficiency value and stores that energy value as the charging target. Then, as your car keeps updating your efficiency, but not the energy target, it shows you more or less range for what is actually the same battery charge. Such changes would decrease over time if you are the only driver and mostly drive a predictable commute, but would increase after a long road trip or if another driver takes over for a while, etc.

So I'd suggest you check the battery display in terms of units other than miles of range (you can change that in the settings) and see if you still observe a lot of variation.

(Of course, it could just be excessive drain while the car is sitting idle; that seems to have come down to close to nothing in the last few months through software releases, but there are non-Tesla sources of drain, such as Teslafi or other non-Tesla services that communicate with your car.)