Battery charges to 80% then jumps to 83% 30 mins later

[gottagofast]

I have my charging set up to stop charging at 80% and it does stop charging at 80%, it shows the car is at 80%

But then 10 to 30 mins later it’s now at 83% and it wasn’t even charging, I looked at it and no power was going through the charger after it finished at 80%

So is the car really still at 80% and it just had more range than it thought so it’s displaying more even though it’s at 80%? Or is it really at 83%

 

[Candleflame]

thats normal. means the battery isnt calibrated and you have to wait to the next battery calibration. If it charges to 80% but then compares itself to the voltage table and jumps to 83% the car presumes you have more range than you actually do. I would just keep driving, eventually the car will run a recalibration event. This happens every 2-4 months usually.

 

[ewoodrick]

80% 83 %? It really doesn't matter. 3% extra isn't going to cause the battery to blow up or fail early.

 

[cmaster]

Wow! The car charges itself! Great car!

I see this happen when the temperature increase or sometimes during charging. I set it to 90 for my limit, but, ended being 91 or 92. At first, I thought it was a ghost in the car so I went out to get some ghost charms and put in my car. Then, when I had my car parked at work in the morning, noticed that the car SoC went up. Went out again, and got some more ghost charms.

I just think it's likely a ghost inside the car.

 

[rlsd]

Wow! The car charges itself! Great car!

I see this happen when the temperature increase or sometimes during charging. I set it to 90 for my limit, but, ended being 91 or 92. At first, I thought it was a ghost in the car so I went out to get some ghost charms and put in my car. Then, when I had my car parked at work in the morning, noticed that the car SoC went up. Went out again, and got some more ghost charms.

I just think it's likely a ghost inside the car.

After a good night sleep the car gains more energy.

 

[gottagofast]

So is it really at 80% and it’s just displaying 83%? Or is it actually at 83% I’m confused

Is it telling me my range at 80% is higher than it thought it was before

 

[Rocky_H]

So is it really at 80% and it’s just displaying 83%? Or is it actually at 83% I’m confused

Is it telling me my range at 80% is higher than it thought it was before

The car's estimation of the amount of energy is taking a lot of factors into account, and one of these is the temperature of the battery pack, because this really is how batteries work, that you can get different amounts of energy out of them by how efficient the chemical reactions are, which is dependent on the temperature.

So while it was charging, it stopped at what the estimate thought was the amount of energy to be 80%. But then after it was done, over a half hour or so, the temperature of the battery may drift some, warmer or cooler, and the car's estimation algorithm is adjusting to that newer temperature, and the energy estimate may move a little bit. Trying to measure the amount of energy in a battery isn't as fixed or solid a thing as looking at the level of sugar in a measuring cup. It's a lot of complicated judgements. So yes, this happens all the time, that the battery % may move by 2 or 3 % up or down as the car has been sitting for a while after charging.

 

[Sophias_dad]

Get over the minutiae of charge level! Would you notice or care if your gasoline powered car had 3% more or less gasoline in the tank?

Fun fact, gasoline expands and contracts with temperature too! If I did my math right, gasoline takes 2.85% more volume as it goes from 0C(32F) to 30C(86F).

 

[gottagofast]

The car's estimation of the amount of energy is taking a lot of factors into account, and one of these is the temperature of the battery pack, because this really is how batteries work, that you can get different amounts of energy out of them by how efficient the chemical reactions are, which is dependent on the temperature.

So while it was charging, it stopped at what the estimate thought was the amount of energy to be 80%. But then after it was done, over a half hour or so, the temperature of the battery may drift some, warmer or cooler, and the car's estimation algorithm is adjusting to that newer temperature, and the energy estimate may move a little bit. Trying to measure the amount of energy in a battery isn't as fixed or solid a thing as looking at the level of sugar in a measuring cup. It's a lot of complicated judgements. So yes, this happens all the time, that the battery % may move by 2 or 3 % up or down as the car has been sitting for a while after charging.

Ok so when my battery was cold it said I had 227 miles range at 80%

But since the battery warmed up it displayed 236 miles of range

So that means when my battery is cold I have 227 miles of range at 80% and when the battery is warm i have 236 miles of range at 80%? Even though it’s displaying 83%

 

[ewoodrick]

Ok so when my battery was cold it said I had 227 miles range at 80%

But since the battery warmed up it displayed 236 miles of range

So that means when my battery is cold I have 227 miles of range at 80% and when the battery is warm i have 236 miles of range at 80%?

That's the way batteries work, all batteries.

 

[Rocky_H]

So that means when my battery is cold I have 227 miles of range at 80% and when the battery is warm i have 236 miles of range at 80%? Even though it’s displaying 83%

Well, no. The % calculation is simple math, based on what it thinks the amount of energy is divided by the possible total, which is generally a fixed value. So it will not think that both 227 or 236 rated miles are both equal to 80%. A ratio doesn't work like that. It thought there was some amount of energy in there, which equaled to 227, which is 80%. Then, later, it kept looking, and there seemed to be more, and that new value it estimated was 236, which was 83%.

That's the way batteries work, all batteries.

The estimated energy shifting would be, but it can't think two different energy values equal the same % like that.

 

[gottagofast]

Well, no. The % calculation is simple math, based on what it thinks the amount of energy is divided by the possible total, which is generally a fixed value. So it will not think that both 227 or 236 rated miles are both equal to 80%. A ratio doesn't work like that. It thought there was some amount of energy in there, which equaled to 227, which is 80%. Then, later, it kept looking, and there seemed to be more, and that new value it estimated was 236, which was 83%.


The estimated energy shifting would be, but it can't think two different energy values equal the same % like that.

I should gain miles with a warm battery though not actual kWh which means the battery should still be at 80% after it warms

I didn’t gain 3 kWh (which is around 3%) of energy just from the battery going from 55 degrees to 70 degrees, but I should gain more miles per %

 

[davewill]

I should gain miles with a warm battery though not actual kWh which means the battery should still be at 80% after it warms

I didn’t gain 3 kWh (which is around 3%) of energy just from the battery going from 55 degrees to 70 degrees, but I should gain more miles per %

Ideally, I suppose, but the calculation of the percentage simply uses the estimated overall total capacity of the battery, not adjusted for temperature that I can tell. Part of the reason for that is that it takes multiple charge/discharge cycles for the BMS to come up with a good estimate of the total capacity of the battery.

In fact, habitually charging to anything below 90-100%, especially if paired with not discharging the battery very much, tends to throw off that estimate, and an occasional charge to 100% is one way to recalibrate that. Note that we're only talking about calibrating the estimate of the capacity. The actual capacity is always there, so charging to 100% doesn't really increase the capacity, it merely allows you to see it better.

 

[gottagofast]

Ideally, I suppose, but the calculation of the percentage simply uses the estimated overall total capacity of the battery, not adjusted for temperature that I can tell. Part of the reason for that is that it takes multiple charge/discharge cycles for the BMS to come up with a good estimate of the total capacity of the battery.

In fact, habitually charging to anything below 90-100%, especially if paired with not discharging the battery very much, tends to throw off that estimate, and an occasional charge to 100% is one way to recalibrate that. Note that we're only talking about calibrating the estimate of the capacity. The actual capacity is always there, so charging to 100% doesn't really increase the capacity, it merely allows you to see it better.

So I need to charge to 100% if I want to see what the actual capacity is

And that 100% charge will be higher or lower depending on the battery temp

 

[E90alex]

The charge level % is just the computer’s estimate of the battery SOC based on various factors as already mentioned.

The amount of energy stored in the battery did not change. But it did more measurements while it was at rest and determined there was more energy than it had originally estimated.

The battery computer (BMS) can’t accurately measure the battery level when it’s in use (charging or discharging). So based on previous data, it saw that you charged xx kWh which from its internal calculations that should mean it was at 80%. After it was done charging and sitting, the computer was able to make more measurements to refine its estimate and realized it actually had 83%.

The computer can also artificially reduce the displayed % when cold. You’ll see this as a blue section on the charge level slider.

 

[Rocky_H]

I should gain miles with a warm battery though not actual kWh which means the battery should still be at 80% after it warms

No. All of that is the opposite. I just explained all of this.

I didn’t gain 3 kWh (which is around 3%) of energy just from the battery going from 55 degrees to 70 degrees,

The car's estimation algorithm does think exactly that! It is recalculating, and it DOES think there is an extra 3 kWh of energy available in there because of the temperature shift from 55 to 70 degrees (for example).

but I should gain more miles per %

NO! It's not an efficiency adjustment. It is re-evaluating and now has a different estimate of the amount of energy.

but the calculation of the percentage simply uses the estimated overall total capacity of the battery, not adjusted for temperature that I can tell.

It does also include temperature in its evaluation/estimation.

 

[gottagofast]

something that strange to me is if I go by how many miles the car has at 50% then it appears my degradation is slightly more than 8% but if go by how many miles I have at 80% then my degradation is 10%

My miles at 50% is 143-144, 8% loss
Miles at 80% is 226-227, 10% loss

Original full range is 315

 

[davewill]

So I need to charge to 100% if I want to see what the actual capacity is

And that 100% charge will be higher or lower depending on the battery temp

It's a little more complicated than that. Charging to 100% isn't enough by itself. The BMS needs to see the battery in various levels of charge. so it helps to run the battery level down well below 50%, too.

All of this is further complicated by the fact that even in the coldest weather, the battery will warm as you drive, so a lower reading when you start driving in the morning will adjust as you drive. People don't notice it because they are also consuming power, so the percentage just goes down like normal.

My advice is to not obsess over this stuff too much. Tesla's BMS is actually very good, and you can afford to kind of let it do it's thing, generally. If you want to charge to 100%, and run the battery down a ways every 1-3 months, it might improve the accuracy of the battery gauge by a bit, but if you don't it will work well enough.

 

[ewoodrick]

So I need to charge to 100% if I want to see what the actual capacity is

And that 100% charge will be higher or lower depending on the battery temp

Charging to 100% (and letting it sit to allow the BMS to balance) will only tell you what the car's BMS thinks that the full charge is.

TO see what it really is, you have to take it to 0%. And then you will have the amount available for that charge under those specific conditions. The next time you try it, you will probably get a different number.

While the math of calculating all of this is exact, the batteries themselves are not exact. All of this is the result of highly educated GUESSES!

I remember years ago with a digital SLR camera taking it to the top of the ski slopes and the battery was so dead that the camera didn't even think about turning on. I put the camera away and then skied down to the lodge, where I got the camera out to check it. It turned on with no issues and showed a good charge. I took it back up this time but kept in under my jacket and it worked perfectly.

That's all without charging the battery. The only difference was battery temperature. At the top the first time, the battery obviously had 0% in it. But at the bottom, it was back over 75%. Same battery, same camera, no charging involved.

Battery capacity is more of an art than a science. It's really hard to know where all those electrons are and what they want to do.

 

[ewoodrick]

something that strange to me is if I go by how many miles the car has at 50% then it appears my degradation is slightly more than 8% but if go by how many miles I have at 80% then my degradation is 10%

My miles at 50% is 143-144, 8% loss
Miles at 80% is 226-227, 10% loss

Original full range is 315

Is it less than 70%? If not, nothing can be done, just live with it and enjoy the car as opposed to worrying about it. I really don't know, nor care what the current degradation of either of my cars batteries are, because I know that I can get where I want to. And even 20% difference isn't going to change anything that I do.