Strange charge level percentage after charging

[mvrlogins]

My Model X was plugged in last evening to a street lamp charger at 10% with the target set to 90%.

Got a notification from the Tesla app this morning that the charge has been completed at 90%

The ubitricity (street lamp provider) invoice email shows a total usage of about 83 kWh (car is a 100 kWh model)

Tesla app (in Charge Stats) shows I added 71 kWh

Teslamate shows that the usage was about 83 kWh (matches invoice above) but car added 71kwh to go from 10% to 90% (?)

Get in the car this morning and dash shows charge level at 96% !!

So now I'm totally confused. I understand the difference in the ubitricity usage and actual added kwh as it relates to efficiency, etc.

But how did a 100 kWh battery car go from 10% to 90% with only 71 kWh added?

And why is the car now showing 96%?

 

[Dilly]

I get this occasionally in my M3 on my home charger. I suspect it’s down to temperature changes.

I always charge to 80% (234 miles). Sometimes I’ve ended up with 245 miles!

I wouldn’t worry. The car is calculating based on all the factors.

 

[mvrlogins]

I don't think it's do with mileage/temperature. I not using mileage in the calculations, only percentages and kWh - which are not affected by weather.

Adding 70kwh to a 100kwh battery is a 70% increase regardless of the weather.

The question is if you've ever set the charge to 80% and ended up with 86% while only adding 60% charge from 10%

I don't use mileage in general to see the range, only percentages, because mileage displayed is affected by too many factors. Having had the car for almost 7 years, I've gotten quite comfortable with it. But that debate has been had many times on this forum and elsewhere.

 

[qwickshot]

A 100kwh battery isn’t 100kwh usable, it’s 90kwh (ish).

There are charging losses when going from AC to DC. The car can also consume power doing any housekeeping on the MCU, reporting back to the mothership etc., heating and cooling the battery or charger. All of this can consume >10% of the power added, the charging losses are the biggest factor.

The Tesla API can return 2 values, power added to the batter and power consumed by the car. The former is what ends up in the batter and the former factors in any losses or power used by the car.

 

[btc1k]

It is affected by the weather, as temperature is a component of the weather.

When temperatures drop, the internal resistance of the battery is increased. This means that it requires more effort by the battery to charge, in turn lowering the capacity. The internal resistance of all batteries rises when cold. taking extra energy to overcome.

 

[mvrlogins]

A 100kwh battery isn’t 100kwh usable, it’s 90kwh (ish).

There are charging losses when going from AC to DC. The car can also consume power doing any housekeeping on the MCU, reporting back to the mothership etc., heating and cooling the battery or charger. All of this can consume >10% of the power added, the charging losses are the biggest factor.

The Tesla API can return 2 values, power added to the batter and power consumed by the car. The former is what ends up in the batter and the former factors in any losses or power used by the car.

May I ask where you got the first statement about the usable capoacity? I haven't seen that before. I'd like to know more about that

In the past, it's always been the case that when the API returns 10kwh added (not used from the charger, that's always higher) I've always seen an addition of 10% that implies a 100 kwh battery being used fully or almost fully.

I said in the first post that the charger used 83 kwh and the car added 71 kwh and that I expected that - that's the part that deals with your second paragraph

The 2 values in the API are what I mention in my 5th sentence of the first post

 

[mvrlogins]

It is affected by the weather, as temperature is a component of the weather.

When temperatures drop, the internal resistance of the battery is increased. This means that it requires more effort by the battery to charge, in turn lowering the capacity. The internal resistance of all batteries rises when cold. taking extra energy to overcome.

Again, that is dealt with in the diffence between 83 kWh and 71 kwh as I said in my first post.

The car api is stating that it "added" 71 kwh but "used" 83 kwh. I get that.

The problem is that the car battery percentage shows I added 80% from 70 kwh and then shows 96% after finishing charging at 90%

Unless my battery was made smaller overnight

 

[qwickshot]

My bad it’s about 95kwh.

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All lithium ion batteries have a ‘gross’ capacity and a ‘usable’ capacity. Tesla don’t actually advertise their battery capacities but it’s well known that the 100 pack is in fact 100kwh gross.

All car batteries have a reserved amount at the bottom of the pack which you can’t use. It’s there to protect the pack, if a lithium battery drops below a certain voltage it is damaged beyond repair.

Manufacturers assume people are dumb and will leave their cars are low SOC for long periods of time. If they don’t someone might park up on 2% with a warm and leave it a week. If they didn’t have the bottom reserve, the pack voltage could drop below the minimum safe level and degrade or even kill the cells/pack.

Some manufacturers also build in a reserve at the top of the pack to hide degradation and give the illusion of faster charging speeds at high SOC. In reality you are not charging it to it’s true 100% hence why it’s a bit faster. This of course comes at the expense of headline range.

 

[btc1k]

Again, that is dealt with in the diffence between 83 kWh and 71 kwh as I said in my first post.

The car api is stating that it "added" 71 kwh but "used" 83 kwh. I get that.

The problem is that the car battery percentage shows I added 80% from 70 kwh and then shows 96% after finishing charging at 90%

Unless my battery was made smaller overnight

Ok, and the % is measured by changes in pack voltage which changes depending on other variables, such as temperature

 

[LikesToys]

The power provider will display the amount of AC they provide, while the cars inverter could loose about 10% converting the AC to DC. So you put in a lot less into the battery than you are delivered by the power provider.

 

[Lockey]

I have a vague recollection that 70kWhr of my 75kWhr battery is it's usable range (for the reasons described above) which is backed up by the car taking approx an hour for 10% increase in SOC when I'm pulling 30A off a charger (I don't usually pull the full 32A as I've had chargers with flakey breakers trip in the past).

So if you have a 95kWhr battery with 90kWhr usable capacity 71kWhr is about 80%. It is a bit odd that the car then showed 96%, a couple of % difference for the battery being cold I could go with.