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Failed range calculation left me stranded

So I am on my way home with a reasonable amount of range in excess of my destination (home). Not excessively hot, dusk, normal driving conditions. I have roughly 6 miles of range left for my 2.5 miles remaining when I get a warning that the vehicle is shutting down, and I end up stranded 1.4 miles from home with 4 miles of range reading. Outside temp 76F. How is this not an error on the vehicle's part? I get that you cannot rely on there being excess range after zero, but now you cannot trust that the range provided is accurate?! How can one trust the vehicle at all? I am no stranger to dealing with these cars, and have put over 100K miles between our Model S and Model X, but in my opinion the inability of the car to accurately represent it's remaining range is unforgivable. I hope that Porsche does it better, because Tesla just lost a former fanboy.
 

TexasEV

Well-Known Member
Jun 5, 2013
7,656
8,936
Austin, TX
It’s no different “now”, you never could trust that the range is that accurate. Battery state of charge can not be measured directly. In any car, even a Porsche. It’s always an estimate, and it can be more or less accurate depending on how you’ve charged recently. You just shouldn’t be cutting it that close. Sorry, I don’t agree that you had a “reasonable amount of range in excess of your destination”.
 

commasign

TeslaAdviceBlog.com
Aug 31, 2013
3,202
4,301
Davis, CA
First I've heard of a Tesla shutting down before the zero. We know not to trust the listed range, but I too would have assumed a listed range of 6 miles would have been enough to cover 2.5 miles. I.e. if I was 2.5 miles from home and my range said 6 miles, and there was a L2 charger a block away, I would not stop to charge.
 

Krugerrand

Enough of the 🐩, back to 🐈‍⬛
Jul 13, 2012
12,983
90,670
Tesla friendly place
The range calculation should always be an underestimation. End of story.

Why? So you can then say, ‘it’s okay, I can drive another 8 miles before I really hit 0’. And then come here to report it only went 7 below 0 and you got stranded again?

How about just being reasonable and logical and not running the battery down to nothing? It’s just like driving a fossil fuel car, run it to E often enough and eventually you’re going to have to walk the rest of the way.

Zero sympathy. End of story.
 
Last edited:

xyeahtony

Active Member
Mar 21, 2017
2,148
2,694
Louisiana
Why? So you can then say, ‘it’s okay, I can drive another 8 miles before I really hit 0’. And then come here to report it only went 7 below 0 and you got stranded again?

How about just being reasonable and logical and not running the battery down to nothing? It’s just like driving a fossil fuel car, run it to E often enough and eventually you’re going to pay to have to walk the rest of the way.

Zero sympathy. End of story.

It is also well known and common knowledge that it is technically difficult to calculate how much usable energy is left in a battery. The science and technology behind measuring how much power you have left in a battery is shoddy at best. Combined that with a computer that has to extrapolate how many miles it thinks you can drive, that's asking for trouble.
 
Calculating battery state of charge is not like measuring the amount of fuel in a gas tank. The only 100% accurate measurement is made by draining the pack at which point the value is no longer any use to you. Otherwise it's measured through indirect proxies like pack voltage, voltage change rate, delta between measured charge and discharge power, etc. It's like measuring how full a barrel of water is by listening to the sound when you bang on the outside or watching how fast it pours out when you open the spigot.

Tesla does actually design their capacity reporting to attempt to over-estimate on the low end. There are many stories of people driving several miles past "0" but you can't count on it because it's just a (fairly accurate - relatively speaking) estimate. You were just unlucky to be a few miles off in the other direction.

I sympathize with your frustrating experience, but now you know better about the state of battery capacity measurement so you're equipped to avoid this situation with future EV trips.
 

EVSteve

110% Solar Powered
Jul 14, 2014
386
437
Davenport, FL
Let’s compare. How many of us would continue to drive an ice car if it said 6 miles of range left? Most wont even show a distance to empty below one gallon for this very reason.

It’s also my understanding it’s bad for the cells to go below 10%? Correct me if my assumption is off. Why anyone would do this then complain when the car shuts down is beyond my comprehension. There were no places at all to put an extra kWh or two in the battery? Come on.
 
As lithium batteries age their internal resistance increases, which in turn reduces the amount of current which can be drawn from the batteries for a given voltage level. The battery pack has hard cut off limits for the voltage ranges, so to try preventing an early trip of the lower cut off voltage, Tesla puts a power limit in place at low charge levels. This helps but is not 100% fool proof, especially if you suddenly draw a lot of power or if a given module is weaker than others due to aging, then the cut off limit could potentially be hit earlier than predicted.
 
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xyeahtony

Active Member
Mar 21, 2017
2,148
2,694
Louisiana
Although I won't lie, I've driven my car down to 3 miles before. but if I ended up stranded, I wouldn't have been mad at Tesla since it was my own damn fault for bringing the car down that low, and I most certainly would've have thrown my arms up in the air and declare im buying a whole new different car after one incident lol.
 

commasign

TeslaAdviceBlog.com
Aug 31, 2013
3,202
4,301
Davis, CA
Again, this is the first time I’ve seen a post about a Tesla shutting down above zero (have there been others?). So it’s a useful PSA type learning experience worth sharing among the Tesla community. I can’t be the only person that would have thought the same as the OP in this scenario. Now I know differently. Learn something new every day on these forums.
 
Again, this is the first time I’ve seen a post about a Tesla shutting down above zero (have there been others?). So it’s a useful PSA type learning experience worth sharing among the Tesla community. I can’t be the only person that would have thought the same as the OP in this scenario. Now I know differently. Learn something new every day on these forums.
It is not that unusual, the range will only be an estimation based on the calculated energy left in the battery. It is not a exact measurement but an (often good) estimate.

 

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