Yet another 100% charging question

[canbonbon]

MYLR 2023. Bought the car on Feb 28th and they charged it to 100% before handing off to me. It was on one of the Level 2 chargers located at the back of the pickup area. The miles were 330. I did not charge 100% again until sometime in August when I was driving long distance. The 100% charge showed 321 miles. Charged again to 100% during that trip and consistently got anywhere between 317 to 320. Did not charge again until December 2023. This time it only charged to 311 miles. I assumed all this was natural degradation and did not pay any attention. Other than those instances, I kept the car around 80-85% max charge and that was sufficient for my driving routine. Fast forward this week. I had to charge the car again to 100% for travel and for some reason it charged to 327 miles. I thought its a fake reading and drove to my destination which was around 180 miles. On the way back, charged again to 100% and this time its again did 326.

So now I am confused. Isn't it supposed to go down after a year? Or are the miles charged to 100% is totally unpredictable? If it went consistently down, that's acceptable. But it went down and then went up? Not sure what is going on. But I am losing faith in those numbers. I just wanted to post this so that people who have more knowledge than me about how charging works may comment on this. I think it might benefit the rest of us who are baffled with this behavior.

 

[shahryaran]

Is battery calibration pointless?!

Let's say your car has some amount of battery degradation and you can't get the range you want. You were told to calibrate battery and you may get some range back. Here is the thing... It doesn't matter and don't worry about it. The fact is that the actual amount of battery capacity is there...

teslamotorsclub.com

 

[Sophias_dad]

2% is noise. Be happy, and please don't start another thread when it goes down 3%

 

[father_of_6]

My phone says my battery is at 43%, but I'm almost certain it's actually 43.4% or 42.891%... lies... LIES!!!

 

[Resist]

MYLR 2023. Bought the car on Feb 28th and they charged it to 100% before handing off to me.

So Tesla charged it to 100%? They know better than to not do that!

 

[gsmith123]

But I am losing faith in those numbers.

Well they are just best guesses. You shouldn’t put too much faith in them.

 

[canbonbon]

2% is noise. Be happy, and please don't start another thread when it goes down 3%

I totally get that my post is worth making fun of (which a few folks did) but my point stands. The car is capable of going down and then coming back up. Which what I was I trying to say to others who might notice something similar. Yes its not that our life depends on 1% here or there but personally I did not know that it could also go up. The general feeling on the board is that it gradually goes down and during the first year, the degradation is max. Also saw this recent video on Battery degradation.

In the video he correctly says that charging to 100% should be headache for the manufacturers to solve instead of car owners worrying about it. They are short changing us by selling a product but saying oh you cannot use all of it because the very fact that you use it, could damage it and reduce its life. Imagine if an umbrella seller says this to you: "Oh my umbrella is the best in the world and it will last you a lifetime. Just save it from Rain and the sun because that will shorten its life." What the F***, that is the reason I bought the car so that I can drive it without having to charge it so often. I am lucky enough to have a charger at home, but if I did not, then I would have preferred to charge 100% (weekly) so that I am not making frequent visits to a charger (which is what we normally do with a gas car). So enough of this BS about don't charge your car to 100% all this sounds like folks are happy accepting an lower grade product.

 

[canbonbon]

So Tesla charged it to 100%? They know better than to not do that!

My home charger was not installed at that point, so he maximized it to avoid any issues. It was NOT done on my request as I did not know at that point that charging to 100% is such a taboo because I charge my iPhone daily to 100% and never worry about any battery loss due to it.

 

[nailer]

I totally get that my post is worth making fun of (which a few folks did) but my point stands. The car is capable of going down and then coming back up. Which what I was I trying to say to others who might notice something similar. Yes its not that our life depends on 1% here or there but personally I did not know that it could also go up. The general feeling on the board is that it gradually goes down and during the first year, the degradation is max. Also saw this recent video on Battery degradation.

In the video he correctly says that charging to 100% should be headache for the manufacturers to solve instead of car owners worrying about it. They are short changing us by selling a product but saying oh you cannot use all of it because the very fact that you use it, could damage it and reduce its life. Imagine if an umbrella seller says this to you: "Oh my umbrella is the best in the world and it will last you a lifetime. Just save it from Rain and the sun because that will shorten its life." What the F***, that is the reason I bought the car so that I can drive it without having to charge it so often. I am lucky enough to have a charger at home, but if I did not, then I would have preferred to charge 100% (weekly) so that I am not making frequent visits to a charger (which is what we normally do with a gas car). So enough of this BS about don't charge your car to 100% all this sounds like folks are happy accepting a lower grade product.

Think of it this way. A petrol engine can safely operate at 4-5000 RPM. But if you drove it like that all the time how long would it last.

It’s the same for your battery. You can charge it to 100% every day if you like but don’t expect 150k miles without any degradation. However if you keep it under 55% and charge to 100% just before you need it you might get 300k miles with less than 10% degradation.

It’s totally up to you how you charge/drive your car, same as an ICE. You can drive it like you stole it every day if you like.

I find it annoying that the manufacturers don’t explain clearly the effect of storage SOC on degradation. All I hear everywhere is 80%, which is possibly the worst storage SOC to use. You have to come to places like this for real world scientific advise.

 

[ucmndd]

I did not know at that point that charging to 100% is such a taboo

It’s not. If you want to charge to 100% once a week or multiple times a week that’s perfectly fine. It’s absolutely not “taboo” and the detrimental effects of doing so are vastly overstated.

I charge my iPhone daily to 100% and never worry about any battery loss due to it.

Your phone manages battery health too, if you let it:

 

[nailer]

I charge my iPhone daily to 100% and never worry about any battery loss due to it.

So do i and the battery is usually half dead after 2 years and I buy a new phone. I’d be hoping my car lasts a bit longer.

 

[HitchHiker71]

The GOM (Guess-O-Meter) is just that - an estimate. The estimated mileage doesn’t have anything to do with actual battery health or degradation. Only KWh matters when it comes to attempting to determine the amount of battery degradation. Switch to percentage and stop using the mileage indicator as it’s really not very accurate anyways.

 

[Big Earl]

The GOM (Guess-O-Meter) is just that - an estimate. The estimated mileage doesn’t have anything to do with actual battery health or degradation. Only KWh matters when it comes to attempting to determine the amount of battery degradation. Switch to percentage and stop using the mileage indicator as it’s really not very accurate anyways.

The rated range display on a Tesla is not a GOM. It displays the energy remaining in the battery in units of rated miles, which are calculated based on the EPA rated range. If you have a 100 kWh battery in a car that's rated at 300 Watt hours per mile with no degradation, 100% will show 300 rated miles. 50 kWh battery in a car rated at 400 Watt hours per mile = 200 rated miles @ 100%.

The rated range number will move around a little bit based on an imperfect calculation and overall battery degradation. Some fluctuation is to be expected, and the overall trend will be a slow decline over time.

Estimated range based on recent driving can be viewed on the energy graph. That's the GOM.

 

[shahryaran]

So do i and the battery is usually half dead after 2 years and I buy a new phone. I’d be hoping my car lasts a bit longer.

Phone batteries chemistry is different.

 

[E90alex]

So do i and the battery is usually half dead after 2 years and I buy a new phone. I’d be hoping my car lasts a bit longer.

A phone has much smaller battery and also the device itself has a much shorter expected life than a car.

Not charging to 100% would benefit the phone as well but it often is impractical as it may not last you the whole day and you’ll have to find a charger mid day.

And even when charging a phone to 100%, you typically use a majority of the battery capacity per day so it’s a large depth of discharge which is not ideal for battery health.

Compared to a car, the typical daily usage may only require 10-20% of the battery so it’s much easier to keep it at a lower charge without inconveniencing yourself.

 

[tga]

the energy remaining in the battery

But it's actually surprisingly difficult to determine this. Determining state of charge (ie, "energy remaining in the battery") from resting voltage is a bit of an estimate. You can measure the amount of power added with a full charge, but even that is an estimate, since no battery has 100% round trip efficiency (some power is lost in heating).

It's even harder on LFP's with a flatter discharge curve, which is why Tesla recommends once per week 100% charge on LFP cars.

 

[HitchHiker71]

The rated range display on a Tesla is not a GOM. It displays the energy remaining in the battery in units of rated miles, which are calculated based on the EPA rated range. If you have a 100 kWh battery in a car that's rated at 300 Watt hours per mile with no degradation, 100% will show 300 rated miles. 50 kWh battery in a car rated at 400 Watt hours per mile = 200 rated miles @ 100%.

The rated range number will move around a little bit based on an imperfect calculation and overall battery degradation. Some fluctuation is to be expected, and the overall trend will be a slow decline over time.

Estimated range based on recent driving can be viewed on the energy graph. That's the GOM.

It has all but been proven that north of 50% the Tesla GOM over estimates range and as the SoC decreases the estimator provides more accurate estimation - hence it really is a GOM - you can disagree of course - to each his own. There's an EPA investigation regarding this exact issue at present. The entire BMS is in reality an estimation game - it is very difficult to determine exactly what the true SoC is within a battery pack. Tesla's BMS likely does a better job than just about anyone else out there - but it's still all estimation at the end of the day. This is why some cars are able to go beyond zero battery percentage (or zero miles) whereas other cars actually die before reaching zero. The estimations of SoC are exactly that - estimations - whether in % or miles.

 

[HitchHiker71]

But it's actually surprisingly difficult to determine this. Determining state of charge (ie, "energy remaining in the battery") from resting voltage is a bit of an estimate. You can measure the amount of power added with a full charge, but even that is an estimate, since no battery has 100% round trip efficiency (some power is lost in heating).

It's even harder on LFP's with a flatter discharge curve, which is why Tesla recommends once per week 100% charge on LFP cars.

Exactly - well said.

 

[fholbert]

So Tesla charged it to 100%? They know better than to not do that!

Not an issue to occasionally charge to 100%, some say it’s needed to recalibrate everything. I do it when a trip is planned. In cooler temps I save the last 5% until I get in the shower so the battery is ready to go.

Sure beats the guy taking delivery with a 30% charge having to stop at a SC to make it home.

 

[David99]

Here are my range fluctuation over the first 4k miles.

The actual range does not fluctuate. Your battery doesn't get worse and then better. It's the BMS's best guess at any point in time.

The closer you drive to 0%, the more accurate the estimation gets. The BMS dynamically adjust remaining range based on realtime data from the battery.

The best estimate the car gives you is the energy graph when starting the navigation to your destination. It projects the energy usage based on the route you are going to drive on. It adjusts for elevation and uses a massive amount of fleet data collected by Tesla over more than 10 years.