Incorrect Supercharging Cost in the car vs what is billed

[Resist]

So last week I used a Supercharger and when done my display showed I received 31kWh of power at $0.38/kWh for a total cost of $12.45. After doing the math the end total is clearly incorrect. When I checked my account on Tesla.com it showed the correct numbers, $12.16 for 32kWh of power. So ups with my car always showing the wrong numbers?

 

[jmaddr]

I wonder if it has to do with the announcement a few months ago they were going to charge for all power consumed and not just that which goes towards the battery (AC, screen, etc).

Since it also reports only integers for the energy delivered, maybe there are fractions of a kWh at play here.

You would think they should match though.

 

[Rocky_H]

That is not recent; they have always had a little bit of a discrepancy there, and I do think it has to do with what the car measures, versus what the Supercharger station can measure that it is using from the grid, because of losses.

 

[RayK]

Starting about two years ago, and continuing for one year, I would sometimes see that my Supercharging cost would re-adjust when I disconnected and left the station. There was one cost when the charging stopped but was still connected, then while driving away it would change (lower). Mostly it was an increment of the cost/kWh, $0.28 or so, but a couple of times it would nearly be, or exceed, $1. I couldn't figure out if it was a correction for the times I was running the A/C while waiting for the charge to complete, or when I would watch Netflix while waiting, or some other power-consuming event not directly related to charging the main battery. Over the last year I don't think I have seen this cost adjustment, even though I have not substantially changed my actions while charging the car. If it makes any difference I generally use a 72kW Supercharger near my house (Blossom Hill Road, San Jose).

 

[Resist]

I wonder if it has to do with the announcement a few months ago they were going to charge for all power consumed and not just that which goes towards the battery (AC, screen, etc).

I understand that but then my actual bill would have been higher, not lower. But during this particular charge, I didn't have anything on except the display to watch the charging. Either way the screen showed the total came to $12.45 for 31 kWh of juice at $0.38/kWh. And that math isn't correct. 31 x .38 is $11.78.

 

[RayK]

Either way the screen showed the total came to $12.45 for 31 kWh of juice at $0.38/kWh. And that math isn't correct. 31 x .38 is $11.78.

Nor is the $12.45 for 31kWh @ $0.38. There must be some rounding error / misstatement as the cost would be $12.54 or $12.16.

 

[Twiglett]

I understand that but then my actual bill would have been higher, not lower. But during this particular charge, I didn't have anything on except the display to watch the charging. Either way the screen showed the total came to $12.45 for 31 kWh of juice at $0.38/kWh. And that math isn't correct. 31 x .38 is $11.78

From what I remember, the car is an estimate and it doesn't always accurately estimate the total cost - as @Rocky_H and @jmaddr mentioned.
If you're sat in the car watching a video with the AC blasting it always throws it off.

 

[Resist]

Nor is the $12.45 for 31kWh @ $0.38. There must be some rounding error / misstatement as the cost would be $12.54 or $12.16.

Read my post again, because that's what I said. The $12.45 total for 31kWh @ $0.38/kWh is incorrect. Checking my account online showed I actually received 32kWh of power, which cost me $12.16 @ $0.38/kWh. So the car's display total after Supercharging is always incorrect, which doesn't make sense to me because it should know exactly how much power the took and at a very minimum even with incorrect numbers on the display, the math should have been correct for those numbers, which it isn't.