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charge cost difference between app vs invoice

My recent 2 charges at a supercharger has shown two different cost between what the car app indicated, and what was actually shown on the invoice.
the cost shown on the actual invoice was about a dollar less than what the charging screen showed.
has anyone experienced this? and can anyone advise why this is the case?
 

RayK

Safety Score 90 (Was 96!)
Apr 5, 2016
3,161
3,304
San Jose, CA
I've seen this several times over the 4+ years I've owned my car. Either a "discount" of one or more multiples of $0.xx/kWh, to a completely free session which never showed up on my Tesla account or the credit card attached to it. I don't believe that I've ever heard an official reason but perhaps we are being charged for the actual amount of energy going into the battery and that whatever "extra" power that is being used to run the A/C and the other systems in the car is not. You could also have been at a tiered station and that you crossed over to a lower rate during your charging session.

I've never actually checked the phone app to see what it is reporting. I only go by what appears on the screen in the car but you would think that they would be synced and that the system could properly handle the cost changes. The times I've gotten a discount, the total Supercharging cost on the screen changes almost immediately after disconnecting from the station.
 

RayK

Safety Score 90 (Was 96!)
Apr 5, 2016
3,161
3,304
San Jose, CA
the cost shown on the actual invoice was about a dollar less than what the charging screen showed.

...a "discount" of one or more multiples of $0.xx/kWh
@jdcollins5 Your experience is then opposite of what @boypaulkim and I have seen on our transactions with Tesla Supercharging. We are getting billed less than what the screen(s) are saying. Here in CA I have assumed that all taxes, if any are being assessed at all, is already built into the cost per kWh that is being billed. It's the same as gasoline; all state and local taxes are baked into the displayed $/gal. I'd be very surprised if NC doesn't do the same.
 
The car is showing the DC kWH calculated charge. The invoice is showing the actual AC kWH utility charges at the meter. There are AC-DC losses plus taxes.
I rather doubt that. The utility metering wouldn't be split per plug, and would be hard to coordinate with the connection data. Plus some locations have solar which wold further complicate billing via utility charges.
 
@jdcollins5 Your experience is then opposite of what @boypaulkim and I have seen on our transactions with Tesla Supercharging. We are getting billed less than what the screen(s) are saying. Here in CA I have assumed that all taxes, if any are being assessed at all, is already built into the cost per kWh that is being billed. It's the same as gasoline; all state and local taxes are baked into the displayed $/gal. I'd be very surprised if NC doesn't do the same.
My invoices in NC includes the taxes and is listed separately in the invoice.

Also when I say costs more, I only mean a few cents.
 

RayK

Safety Score 90 (Was 96!)
Apr 5, 2016
3,161
3,304
San Jose, CA
My invoices in NC includes the taxes and is listed separately in the invoice.

Also when I say costs more, I only mean a few cents.
Very strange that you are being separately charged tax(es), at least in my opinion. Here's a copy of one of my recent transactions:

1668536400980.png


edit: The $6.80 cost did appear on my car's screen and did not adjust (upward or downward) after I disconnected. I hope to video a case where the cost changes and post it.

edit2: I found this at Alternative Fuels Data Center: North Carolina Laws and Incentives

"Alternative Fuel Tax Exemption
The retail sale, use, storage, and consumption of alternative fuels is exempt from the state retail sales and use tax.
"

@jdcollins5 If you are being charged a tax to Supercharge, I'd try to find out who is assessing it. Maybe a local entity?
 
Last edited:

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
14,966
19,326
San Diego
@jdcollins5 Your experience is then opposite of what @boypaulkim and I have seen on our transactions with Tesla Supercharging. We are getting billed less than what the screen(s) are saying. Here in CA I have assumed that all taxes, if any are being assessed at all, is already built into the cost per kWh that is being billed. It's the same as gasoline; all state and local taxes are baked into the displayed $/gal. I'd be very surprised if NC doesn't do the same.

The number of kWh added displayed on the screen is not the number of kWh added to the battery (it's off by 4.5%; the number displayed on the screen and in the app is higher by 4.5% than the number of kWh actually added to the battery - this is well known and verifiable - the number on the screen is just the number of rated miles added multiplied by the charging constant (which does not represent the energy per rated mile added; it is 4.5% high)).

I think to answer this question you'd really need a large charging event where what was documented on the vehicle screen and in the app was captured, and in addition the billing information was posted here.

And even then that might not answer it.

But lower billed amounts than displayed would be partially due to the 4.5% factor.

For a 50kWh charge the difference would be a couple kWh, so less than a dollar in most cases I guess.
 
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RayK

Safety Score 90 (Was 96!)
Apr 5, 2016
3,161
3,304
San Jose, CA
The number of kWh added displayed on the screen is not the number of kWh added to the battery (it's off by 4.5%; the number displayed on the screen and in the app is higher by 4.5% than the number of kWh actually added to the battery - this is well known and verifiable - the number on the screen is just the number of rated miles added multiplied by the charging constant (which does not represent the energy per rated mile added; it is 4.5% high)).

I think to answer this question you'd really need a large charging event where what was documented on the vehicle screen and in the app was captured, and in addition the billing information was posted here.

And even then that might not answer it.

But lower billed amounts than displayed would be partially due to the 4.5% factor.

For a 50kWh charge the difference would be a couple kWh, so less than a dollar in most cases I guess.
So I just went back in my charging notes and found the instances where I saw the billed amount change on screen in my car just after the session was finished. Unfortunately I do not directly keep track of the state of charge (SoC) percentage or the kWh value.

Code:
                                       $/kWh         Displayed range
  Date    Orig cost  Adj cost   Diff    Rate   X   Start  Finish  Gain
10/26/19   $ 7.00     $ 6.16   $0.84   $0.28   3    207    305     98
11/05/19   $ 5.04     $ 4.48   $0.56   $0.28   2    207    281     74
11/09/19   $ 7.84     $ 6.72   $1.12   $0.28   4    182    290    108
11/25/19   $ 6.72     $ 6.16   $0.56   $0.28   2    162    260     98
12/10/19   $ 7.84     $ 7.00   $0.84   $0.28   3    158    270    112
12/19/19   $ 6.72     $ 5.60   $1.12   $0.28   4    199    291     92
01/02/20   $ 7.56     $ 6.44   $1.12   $0.28   4    174    277    103
01/05/20   $ 9.80     $ 8.68   $1.12   $0.28   4    137    277    140
02/04/20   $10.64     $10.36   $0.28   $0.28   1    158    305    147
04/30/20   $10.08     $ 9.80   $0.28   $0.28   1    132    278    146
07/13/20   $ 5.88     $ 5.60   $0.28   $0.28   1    211    288     77
04/08/22   $ 8.01     $ 7.92   $0.09   $0.29   -    137    272    135

Column titles should be self-explanatory. "X" is the number of $/kWh increments which if multiplied by the kWh rate, equals the cost difference (Diff) between the Orig(inal) and Adj(usted) costs. This is what convinces me that the adjustments are being done in units of $/kWh and not a percentage of the values; that would yield non-integer multiples.

Two sessions where I added the most range (147 and 146 miles) only had a $0.28 difference from what was initially displayed on my screen and what I was actually billed on my credit card. So they track each other but the ending SoC is different (100% and 90+%). However, if you look at range gains of 140 and 135, both were started at similar SoC (137 miles) and ended about the same (277 and 272 miles) but the cost adjustment was 4X in the first case and 1X in the other. I think that I may have made a transcription error on 4/8/22 in that the original cost was probably $8.21. That would keep the differential in line with the higher cost for Supercharging; it changed from $0.28 to $0.29 per kWh at some point.
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
14,966
19,326
San Diego
So I just went back in my charging notes and found the instances where I saw the billed amount change on screen in my car just after the session was finished. Unfortunately I do not directly keep track of the state of charge (SoC) percentage or the kWh value.

Code:
                                       $/kWh         Displayed range
  Date    Orig cost  Adj cost   Diff    Rate   X   Start  Finish  Gain
10/26/19   $ 7.00     $ 6.16   $0.84   $0.28   3    207    305     98
11/05/19   $ 5.04     $ 4.48   $0.56   $0.28   2    207    281     74
11/09/19   $ 7.84     $ 6.72   $1.12   $0.28   4    182    290    108
11/25/19   $ 6.72     $ 6.16   $0.56   $0.28   2    162    260     98
12/10/19   $ 7.84     $ 7.00   $0.84   $0.28   3    158    270    112
12/19/19   $ 6.72     $ 5.60   $1.12   $0.28   4    199    291     92
01/02/20   $ 7.56     $ 6.44   $1.12   $0.28   4    174    277    103
01/05/20   $ 9.80     $ 8.68   $1.12   $0.28   4    137    277    140
02/04/20   $10.64     $10.36   $0.28   $0.28   1    158    305    147
04/30/20   $10.08     $ 9.80   $0.28   $0.28   1    132    278    146
07/13/20   $ 5.88     $ 5.60   $0.28   $0.28   1    211    288     77
04/08/22   $ 8.01     $ 7.92   $0.09   $0.29   -    137    272    135

Column titles should be self-explanatory. "X" is the number of $/kWh increments which if multiplied by the kWh rate, equals the cost difference (Diff) between the Orig(inal) and Adj(usted) costs. This is what convinces me that the adjustments are being done in units of $/kWh and not a percentage of the values; that would yield non-integer multiples.

Two sessions where I added the most range (147 and 146 miles) only had a $0.28 difference from what was initially displayed on my screen and what I was actually billed on my credit card. So they track each other but the ending SoC is different (100% and 90+%). However, if you look at range gains of 140 and 135, both were started at similar SoC (137 miles) and ended about the same (277 and 272 miles) but the cost adjustment was 4X in the first case and 1X in the other. I think that I may have made a transcription error on 4/8/22 in that the original cost was probably $8.21. That would keep the differential in line with the higher cost for Supercharging; it changed from $0.28 to $0.29 per kWh at some point.
Picked a line of data and couldn't make it line up with anything. (Charged amount seemed too high, so potentially includes conversion costs.)

Just need a recent session with all the data (app logged data, car, billing) , I think, to figure out how this works. As large a charging event as possible.
 

RayK

Safety Score 90 (Was 96!)
Apr 5, 2016
3,161
3,304
San Jose, CA
Okay, so I went out to my usual Supercharger and documented what the car's screen displayed versus what the Tesla app showed for a charge from about 38% to 90%. Bottom line: Displayed cost changed from $16.22 to $15.20 when I disconnected, for a charge quantity of 36 or 38kW (depending upon where you look). Rate was $0.40/kWh so I'll go with 38kW delivered to the car (15.2/0.4 = 38). Contrary to all my previous data, the $1.02 difference is NOT an integer increment of $0.40; it's 2.55x. I sat in the car the whole time and did not run the climate system (I was listening to USB media). Temperature was 58F when I started and 63F at the end of the session (as indicated by the car's sensor). Here's some photos:

Car's screen just after hitting 90% and getting the Charging Complete message (note 36kWh added and $16.22 cost):
Tesla_screen_after_session.jpg


Cost_before.jpg


Car's screen a few seconds later when the charging screen changed:
Cost_after.jpg


Car's screen earlier in the session showing 85% charge (note 41kW charge rate and 32kWh added):
Tesla_screen_almost_done.jpg


Tesla app showing 85% charge a few seconds later when the app updated to 85% (note 47kW rate, the 32kWh added and the heating? [3 S's] icon on the battery line):
Tesla_app_almost_done.jpg


I noticed that throughout the charging session the difference between what the car said was being delivered was 6-7kW lower than what the app indicated. However, the charge added to the car (kWh) was identical.

Tesla app charging history showing today's session (note 38kWh figure):
Tesla_app_history.jpg


And the invoice (again showing 38kW):
Supercharger_invoice.jpg


@AlanSubie4Life Is this enough info? I do have a series of photos and screen captures from the app during the entire session.
 

Attachments

  • Supercharger_invoice.jpg
    Supercharger_invoice.jpg
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AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
14,966
19,326
San Diego
Okay, so I went out to my usual Supercharger and documented what the car's screen displayed versus what the Tesla app showed for a charge from about 38% to 90%. Bottom line: Displayed cost changed from $16.22 to $15.20 when I disconnected, for a charge quantity of 36 or 38kW (depending upon where you look). Rate was $0.40/kWh so I'll go with 38kW delivered to the car (15.2/0.4 = 38). Contrary to all my previous data, the $1.02 difference is NOT an integer increment of $0.40; it's 2.55x. I sat in the car the whole time and did not run the climate system (I was listening to USB media). Temperature was 58F when I started and 63F at the end of the session (as indicated by the car's sensor). Here's some photos:

Car's screen just after hitting 90% and getting the Charging Complete message (note 36kWh added and $16.22 cost):
View attachment 876883

View attachment 876864

Car's screen a few seconds later when the charging screen changed:
View attachment 876865

Car's screen earlier in the session showing 85% charge (note 41kW charge rate and 32kWh added):
View attachment 876879

Tesla app showing 85% charge a few seconds later when the app updated to 85% (note 47kW rate, the 32kWh added and the heating? [3 S's] icon on the battery line):
View attachment 876880

I noticed that throughout the charging session the difference between what the car said was being delivered was 6-7kW lower than what the app indicated. However, the charge added to the car (kWh) was identical.

Tesla app charging history showing today's session (note 38kWh figure):
View attachment 876868

And the invoice (again showing 38kW):
View attachment 876881

@AlanSubie4Life Is this enough info? I do have a series of photos and screen captures from the app during the entire session.
Thanks. Would have been good to have rated miles rather than % for this, but it doesn't really matter.

So:
Added to vehicle battery pack: 36kWh*0.955 = 34.4kWh. (This is only approximate, actually 2 sig figs only, because the 36kWh is rounded - rated miles allow more precision.)

kWh provided by charge station: 38kWh

So since you were doing battery heating, looks like about 3-4kWh was used to heat the battery. And it looks like you are charged for kWh used, not the number added to the battery (as expected).

I can't explain the $16.22 number. Other than it being some sort of estimate prior to disconnecting. I don't know why it would have to estimate anything though, since it knows how much power it has used (and presumably can also ask the charging station to tell it how much has been drawn, though not necessary).
 

RayK

Safety Score 90 (Was 96!)
Apr 5, 2016
3,161
3,304
San Jose, CA
Thanks. Would have been good to have rated miles rather than % for this, but it doesn't really matter.
My 100% rated mileage is 300. I started out the charging session at 115 miles, which is where my 38% SoC came from. I ended the session at 90% and received an indicated range of 270. I'm assuming that all of the intermediate steps in my charging session (I logged 5% increments) were linear percentage-wise.

So:
Added to vehicle battery pack: 36kWh*0.955 = 34.4kWh. (This is only approximate, actually 2 sig figs only, because the 36kWh is rounded - rated miles allow more precision.)

kWh provided by charge station: 38kWh

So since you were doing battery heating, looks like about 3-4kWh was used to heat the battery. And it looks like you are charged for kWh used, not the number added to the battery (as expected).
I did do a few minutes of pre-conditioning prior to arriving at the SC; probably not enough time to make a real difference. It was my first time checking the Tesla app during a charge session in a very long time so I was surprised to see what I assume was a heating icon (the three orange curvy S figures).

I can't explain the $16.22 number. Other than it being some sort of estimate prior to disconnecting. I don't know why it would have to estimate anything though, since it knows how much power it has used (and presumably can also ask the charging station to tell it how much has been drawn, though not necessary).
This has been a fairly common event for me when Supercharging (cost adjustment downward when I disconnect). It hasn't happened every time I SC. Previous "discounts" has been an integer multiple of the cost / kWh. Since I now mostly charge using a CHAdeMO adapter around town, I only have used a SC when I'm at the hardware store (the station I use is next to the Outdoor Supply Hardware parking lot) or while traveling.

I did notice that most of the time where I have seen this cost adjustment was during the "cooler" months (see post #11). I purposely did not run the climate system this time. From my memory, I don't recall using the heater all that much when charging during the cold months but I do run the A/C almost every time I'm charging in the summer.
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
14,966
19,326
San Diego
My 100% rated mileage is 300. I started out the charging session at 115 miles, which is where my 38% SoC came from. I ended the session at 90% and received an indicated range of 270

Ok, so with a LR RWD that would be 76kWh/325rmi * (270displayed rmi - 115displayed rmi) *0.955rmi/displayed rmi = 34.6kWh

So right around what we estimated in this case.

Previous "discounts" has been an integer multiple of the cost / kWh.

I think we can say fairly definitively this is not any sort of "discount" now. We can see that you are likely being charged for the energy used. Why the car displays some estimated number based on a different prediction of kWh used which doesn't reflect reality, we can't say.

Everything seems to align. You added 34.6kWh to the car battery, you used 38kWh, and you were charged for 38kWh.

I did do a few minutes of pre-conditioning prior to arriving at the SC; probably not enough time to make a real difference. It was my first time checking the Tesla app during a charge session in a very long time so I was surprised to see what I assume was a heating icon (the three orange curvy S figures).
Out of curiosity (to figure out how much heating was needed), what was the peak charge rate you saw at ~38%?

I guess the other question is how long the charging session was (we could estimate the heating kW that way - presumably it was fairly constant)?
 
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