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Percentage battery charge is a percentage of what? (2021 MIC M3LR)

JonB

Member
Oct 31, 2021
306
195
UK
Sorry if this has been asked before, I did search.

Regarding the battery charge percentage as displayed in the Tesla App or car display - what is 100% in terms of KWh? Not as straightforward as it looks. For example, I read that Tesla keeps back some of the battery capacity to account for degradation over time, so if my battery is 70KWh, does this mean that "100% charge" is actually 63KWh?

My car is a 2021 M3LR MIC , so I believe the battery's quoted capacity is either 75 or 82KWh (that is from Wikipwedia, but how do I tell for sure?).

Reason for asking is, I get an increase in charge percentage showing in my app, and given the capacity would like to work out how much electricity has been used during a home charging session.
 
Tesla don't say.. they deliver a car that will give at least the advertised range at 100% when new. Beyond that, batteries change, technology changes.. it's a good tactic, as they're not forced to use a specific size battery, they can use whatever is available (in practice due to increasing capacities, it means that the cars are getting longer range over time - something other manufacturers can't do without introducing a new model).
 
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JonB

Member
Oct 31, 2021
306
195
UK
Tesla don't say.. they deliver a car that will give at least the advertised range at 100% when new. Beyond that, batteries change, technology changes.. it's a good tactic, as they're not forced to use a specific size battery, they can use whatever is available (in practice due to increasing capacities, it means that the cars are getting longer range over time - something other manufacturers can't do without introducing a new model).

"At least the advertised range" - a fair point, except it seems like the 360 mile range advertised for my car is a lie, becasue I have not read of anyone achieving that.
 

Fred2

Member
Sep 12, 2019
103
87
Uk
As to your root question, you're in luck - the latest version of the mobile app will show the energy added during a charging session. You can also get a historic view of this data with teslamate, teslafi etc.

Note that in general there are 3 numbers, which won't all be the same
- energy added to the battery
- energy used by the car (so before losses due to the charger in the car, or energy spent on warming battery etc)
- total energy consumed (included losses inside your charge point).

Teslsmate splits out the first 2. Very occasionally it reports energy added > energy used - I think this is when you start with a cold soaked battery, and it is counting the extra energy available from the battery now longer being cold at the end as being energy added
 
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JonB

Member
Oct 31, 2021
306
195
UK
When tested using whatever standard applies where it's sold. They're not allowed to quote anything else.

..which is unfortunate but I guess is the only way for us to compare range between different EV models. Blame the standard, then - much as one might do with ICE cars and their claimed mpg figures (only with them, the discrepancy between claimed and actual is much less).

You will have a 75KWh battery. On your V5 it will show as E5CD battery.

Ah-ha! OK, so E5CD shows in the V5 "Variant" field. Thanks!

As to your root question, you're in luck - the latest version of the mobile app will show the energy added during a charging session. You can also get a historic view of this data with teslamate, teslafi etc.

Note that in general there are 3 numbers, which won't all be the same
- energy added to the battery
- energy used by the car (so before losses due to the charger in the car, or energy spent on warming battery etc)
- total energy consumed (included losses inside your charge point).

Teslsmate splits out the first 2. Very occasionally it reports energy added > energy used - I think this is when you start with a cold soaked battery, and it is counting the extra energy available from the battery now longer being cold at the end as being energy added

That's just the kind of reply I was looking for. I don't plan on using any apps though, becasue I don't want to give 3rd party developers access to my car.
 
Cold is a right battery capacity killer, but I suspect it's not that hard to achieve the advertised range at 25C at a consistent low speed (to minimise drag) with no braking or acceleration -- basically driving for hours round and round a flat test track with no other traffic on it. Standards of this nature need to be really basic to rule out variables, and in this case it makes the test quite hard to replicate in the real world.

For what it's worth, I never came remotely close to any petrol MPG advertised ranges in my real world use either.
 
..which is unfortunate but I guess is the only way for us to compare range between different EV models. Blame the standard, then - much as one might do with ICE cars and their claimed mpg figures (only with them, the discrepancy between claimed and actual is much less).

As with ICE cars it's very much dependent on both the external conditions and the type of driving.

Last week, for example, My 11 mile journey too work without pre-heating the car took 5% of the battery - giving me a theoretical range of ~220 miles from a full charge. The return journey with pre-heating took 3% - giving me a theoretical range of ~360 miles (exactly as advertised).

Fundamentally ICE cars tend to do better with extra-urban driving because that allows the engine to run at better efficiency but EVs tend to do better with urban driving because they recoup energy normally lost to ICE vehicles when braking and they don't use energy while stationary.

All vehicles get worse beyond about 50mph because air resistance becomes a significant factor. James May put it quite well, air starts to get real substance at those speeds around 50 it's like whipped cream and by the time you get to 150 it's like fruit cake.
 
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init6

Active Member
Oct 16, 2020
1,469
904
Scotland
Reason for asking is, I get an increase in charge percentage showing in my app, and given the capacity would like to work out how much electricity has been used during a home charging session.
|It doesn't matter what the % refers to or the size of the battery if what you are trying to work out is how much electricity has been used.

The amount of electricity added to the battery will be less than the amount of electricity used. There are losses in the transfer of the energy from your supply to the battery - especially if you are using an AC charger such as at home. IIRC I get about 11% loss when charging.
If you want to be accurate you should use the amount used by the charger. My podpoint charger gives me that info in the app. I'd be surprised if you don't get that in any other chargers - unless you're using the 3-pin plug type charger.

See also this thread:
and this one:
 
If you want to know more about your battery/ car you have need of Scan my Tesla App, obd adapter and obd module.
 

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Adopado

Well-Known Member
Aug 19, 2019
5,822
4,423
Scotland
"At least the advertised range" - a fair point, except it seems like the 360 mile range advertised for my car is a lie, becasue I have not read of anyone achieving that.

This "lie" accusation is just hyperbolic nonsense. The WLTP range is the only official range that can legally be advertised by Tesla. Of course it's rare to achieve in the real world but nevertheless it is done from time to time.
 

Adopado

Well-Known Member
Aug 19, 2019
5,822
4,423
Scotland
Cold is a right battery capacity killer, but I suspect it's not that hard to achieve the advertised range at 25C at a consistent low speed (to minimise drag) with no braking or acceleration -- basically driving for hours round and round a flat test track with no other traffic on it. Standards of this nature need to be really basic to rule out variables, and in this case it makes the test quite hard to replicate in the real world.

For what it's worth, I never came remotely close to any petrol MPG advertised ranges in my real world use either.

Yes, I have slightly exceeded WLTP in my SR+ on some rare summer days if my actual 50% range was to be doubled. (Obviously I've not started at 100% and run the car until it stops and in need of being trailered home!) I have never achieved official MPG figures in my petrol cars even when really trying.
 

Adopado

Well-Known Member
Aug 19, 2019
5,822
4,423
Scotland
Regarding the battery charge percentage as displayed in the Tesla App or car display - what is 100% in terms of KWh? Not as straightforward as it looks. For example, I read that Tesla keeps back some of the battery capacity to account for degradation over time, so if my battery is 70KWh, does this mean that "100% charge" is actually 63KWh?

Put an added 50% of charge into your battery and note the kWhs that it takes to do that ... then double it. It won't be super accurate but it should give a reasonable idea if done a few times and at different temperatures.
 

JonB

Member
Oct 31, 2021
306
195
UK
It's an intersting illustration but does it include the 2021 LR? Last refreshed Sep 2019. Anyway, I take the point and hope for better when Summer comes.

Regarding my spreadsheet, I will use 75KWh as the capacity for the purposes of working out how many KWh is added, given percentage gain. That is all I really wanted, but of course this does not take account of charging inefficiencies / overhead. I was thinking of adding 10%, does that sound typical for a 230v single phase supply?
 

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