Estimated battery capacity

Faults and Technical chat for the CUPRA Born
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daverik
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Joined: Sun Jan 08, 2023 2:53 pm

Post by daverik »

I have a cupra born with 10000 km. Recently I had the chance to have long trips and tried to calculate/estimate the 0-100% capacity. I have calculated it using the following equation

100%/used% * km driven * consumption in kWh/km

Example: 100%/68% * 221 km * 0.167 kWh/km = 54.3 kWh.

Is it possible that this is due to the following? Nominal capacity 62 kWh, usable capacity 58 kWh but the 0-100% is a few kWh less?

What is your experience?

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Daveion
Posts: 430
Joined: Wed Jun 08, 2022 8:32 pm

Post by Daveion »

Hi Daverik. I wish I could help but have never looked at the capacity versus stated design capacity. I would have thought though there is something a ittle more scientific by way of formula and gathered data to estimate this.
Do you feel that the batteries have degraded?
Born V2-Tech L collected June 22
BMW Z4 e89 sDrive30i Highline
BMW Z4 e85 3.0i SE
Cliffjp
Posts: 53
Joined: Fri Sep 02, 2022 8:12 pm

Post by Cliffjp »

It’s very difficult to determine the percentage capacity of a battery at any point in it’s charging/discharging cycle so any figures displayed by the car are not likely to be very accurate. It should be easier for the car to work out the kWs per unit distance since it can measure the current flow in real time and it knows the distance travelled. I guess the car could calculate the percentage used based on the current drawn over time but it would then be assuming the nominal battery capacity.
TheBornIDentity
Posts: 192
Joined: Mon Jul 18, 2022 5:55 pm

Post by TheBornIDentity »

I made a spreadsheet to help me calculate range and the minimum I can add at faster chargers to get home etc, and there is constantly either a 9% error in the mi/kWh the car indicates or in the battery capacity.

My guess is the trip computer is inaccurate as with petrol cars even though you’d think it would be much more accurate.

My calculator multiplies the mi/KWh by 0.91and is pretty much bang on within 1 or 2 % the prediction unless the conditions change.
Elea4
Posts: 205
Joined: Fri Jun 10, 2022 5:19 pm

Post by Elea4 »

TheBornIDentity wrote: Wed May 17, 2023 11:26 am I made a spreadsheet to help me calculate range and the minimum I can add at faster chargers to get home etc, and there is constantly either a 9% error in the mi/kWh the car indicates or in the battery capacity.

My guess is the trip computer is inaccurate as with petrol cars even though you’d think it would be much more accurate.

My calculator multiplies the mi/KWh by 0.91and is pretty much bang on within 1 or 2 % the prediction unless the conditions change.
Are you including the charging losses? There aren't displayed for the end-user.

For example, the German automobile association club ADAC recorded the following AC charging losses:

2,3 kW / 13,6 %
5,5 kW / 9,2 %
11 kW / 9,0 %

https://www.adac.de/rund-ums-fahrzeug/e ... to-studie/


Re. 54kWh capacity - that matches up with a few other Born and ID.3 reports using Aviloo:

https://www.heise.de/hintergrund/Elektr ... 25021.html
https://aviloo.com/home-en.html

A random google search also came up with someone's Born Aviloo certificate which also says "Available in new condition: 54kWh"

AVILOO-Certificate-Cupra-Born_58_kWh.jpg

Elea4
Posts: 205
Joined: Fri Jun 10, 2022 5:19 pm

Post by Elea4 »

fwiw I've seen various reports (eg. Bjorn Nyland, Chris from the Battery Life channel on youtube, etc.) of the MEB platform having an initial battery degradation of 4-5% in the first year followed by much lower amount in subsequent years.

Why are the 58kWh MEB batteries showing less new capacity, ie. 54kWh instead of 58 kWh? Maybe it's due to reserves somehow not being counted, maybe it's marketing BS... I dunno.

At least the MEB range is in the middle of the pack when compared with vehicles from other manufacturers with similar advertised capacity. Last night I looked at over 100 Aviloo test results from T*slas (thanks Google search lol) and 5-11% battery capacity reduction over the first 1-4 years seemed the norm with only a few outliers showing lesser capacity losses.

All of that said, I'm still a little bit uncomfortable with Aviloo's test methodology when it comes to measuring the total SoH capacity. Fundamentally it's a black-box measurement that's stymied by the fear of manufacturers letting consumers know the real value to potentially prevent battery warranty claims - assuming that number is measurable by the internal systems. Let me be the first to award a prize to a manufacturer that lets consumers easily see the true SoH.

The real value in Aviloo however is in the standardized testing and relative comparison.
TheBornIDentity
Posts: 192
Joined: Mon Jul 18, 2022 5:55 pm

Post by TheBornIDentity »

Elea4 wrote: Wed May 17, 2023 9:13 pm
TheBornIDentity wrote: Wed May 17, 2023 11:26 am I made a spreadsheet to help me calculate range and the minimum I can add at faster chargers to get home etc, and there is constantly either a 9% error in the mi/kWh the car indicates or in the battery capacity.

My guess is the trip computer is inaccurate as with petrol cars even though you’d think it would be much more accurate.

My calculator multiplies the mi/KWh by 0.91and is pretty much bang on within 1 or 2 % the prediction unless the conditions change.
Are you including the charging losses? There aren't displayed for the end-user.

For example, the German automobile association club ADAC recorded the following AC charging losses:

2,3 kW / 13,6 %
5,5 kW / 9,2 %
11 kW / 9,0 %

https://www.adac.de/rund-ums-fahrzeug/e ... to-studie/


Re. 54kWh capacity - that matches up with a few other Born and ID.3 reports using Aviloo:

https://www.heise.de/hintergrund/Elektr ... 25021.html
https://aviloo.com/home-en.html

A random google search also came up with someone's Born Aviloo certificate which also says "Available in new condition: 54kWh"

AVILOO-Certificate-Cupra-Born_58_kWh.jpg
I’d decided that would be too hard to account for so eliminated it. It works on predicted capacity as a percentage. So it will estimate percentage on arrival and percentage required for the next destination. E.g. if the battery is at 37% then the battery capacity should be 58*0. 37 = 22.46 kWh.

The other day it was a lot closer to being correct without the adjustment but it was a warmer day. Could be the battery capacity is only 58 kWh in perfect conditions.
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