Battery Pack Size Larger Than We Thought?

[THEbuz]

Took our first road trip in the 2023 Model Y (LR/AWD), and we barely made it to the first TESLA Supercharger with -4% SOC. (That is correct; NEGATIVE 4% SOC.)

This first TESLA Supercharger location recommended that we charge up to 80% SOC, but I charged a little longer (up to 85% SOC) as a precaution. It was a VERY fast Supercharger @ 250kW, but I could not help but notice that we charged a total of 81kWh (from -4% SOC to 85% SOC). The battery pack is supposedly only 78.1kWh, so, evidently, it is actually larger than that, in reality...??? If we charged 81kWh and the SOC went from -4% to 85%, then the battery pack must be more like 91kWh, no???

 

[Big Earl]

Took our first road trip in the 2023 Model Y (LR/AWD), and we barely made it to the first TESLA Supercharger with -4% SOC. (That is correct; NEGATIVE 4% SOC.)

This first TESLA Supercharger location recommended that we charge up to 80% SOC, but I charged a little longer (up to 85% SOC) as a precaution. It was a VERY fast Supercharger @ 250kW, but I could not help but notice that we charged a total of 81kWh (from -4% SOC to 85% SOC). The battery pack is supposedly only 78.1kWh, so, evidently, it is actually larger than that, in reality...??? If we charged 81kWh and the SOC went from -4% to 85%, then the battery pack must be more like 91kWh, no???

Don't forget the energy used for climate control and battery conditioning while charging. Both of those are included in what you're billed for.

 

[THEbuz]

Don't forget the energy used for climate control and battery conditioning while charging. Both of those are included in what you're billed for.

Thanks for that pro tip and good call out. I can attest that in this case, indeed, we had exited the vehicle within 1-2min of beginning our SC session and used facilities and crossed the street to obtain refreshments. We did sit in the vehicle for about the last 8-12min watching hulu, and I'm certain we did have the HVAC on during that time we sat in the car. (NOTE: Our Model Y is equipped with a heat pump.)

 

[BitJam]

The battery pack is supposedly only 78.1kWh, so, evidently, it is actually larger than that, in reality...???

Tesla increased the size of the battery in the LR and P Model Y almost two years ago. It's now around 82 kWh.

You can get a good estimate of the battery size from the energy consumption screen which shows your expected Wh/mile and range. It's best to do this with a battery SoC of 80% or more to reduce rounding errors.

Battery size (Wh) = Wh/mile x range (miles) / SoC (percent)

For example, if the energy consumption screen says your wH/mile is 250 and your range is 300 miles, and the battery SoC is 90% then your battery size is:

300 x 250 / 0.9 = 83 kWh

IIUC, the battery capacity below 0% is in addition to this.

In addition, the cars are sometimes not great at estimating the current state of charge. Here is a long thread about this:

How I Recovered Half of my Battery's Lost Capacity

Like many others, I have been concerned with loss of 100% indicated battery range on one of my Model 3s. My P3D (build date 9/13/2018, delivery date 10/8/2018) had gotten down to 270.3 miles at 100% charge on January 20, 2020, at about 30,700 miles, which is a loss of 40.8 miles since the car...

teslamotorsclub.com

If you think you are cutting it close to have enough range to get to the next charger then SLOW DOWN!

 

[THEbuz]

Tesla increased the size of the battery in the LR and P Model Y almost two years ago. It's now around 82 kWh.

You can get a good estimate of the battery size from the energy consumption screen which shows your expected Wh/mile and range. It's best to do this with a battery SoC of 80% or more to reduce rounding errors.

Battery size (Wh) = Wh/mile x range (miles) / SoC (percent)

For example, if the energy consumption screen says your wH/mile is 250 and your range is 300 miles, and the battery SoC is 90% then your battery size is:

300 x 250 / 0.9 = 83 kWh

IIUC, the battery capacity below 0% is in addition to this.

In addition, the cars are sometimes not great at estimating the current state of charge. Here is a long thread about this:

How I Recovered Half of my Battery's Lost Capacity

Like many others, I have been concerned with loss of 100% indicated battery range on one of my Model 3s. My P3D (build date 9/13/2018, delivery date 10/8/2018) had gotten down to 270.3 miles at 100% charge on January 20, 2020, at about 30,700 miles, which is a loss of 40.8 miles since the car...

teslamotorsclub.com

If you think you are cutting it close to have enough range to get to the next charger then SLOW DOWN!

Thanks for sharing this formula. Another user shared the same formula (or maybe it was you), and I calculated my battery pack size at 78.1kWh.

As for cutting it close, we drove 60mph basically the entire way, and the SPEED LIMIT was 70mph for much of it, so no doubt we made more than a few truckers angry!

 

[Stirfry]

I find that interesting about the negative SoC. That is crazy that you were able to drive past zero. I understand that it is an estimate by the computer, but still, I would have figured it would just keep it at zero. Probably a little stressful for you as well, glad to made it.

 

[THEbuz]

I find that interesting about the negative SoC. That is crazy that you were able to drive past zero. I understand that it is an estimate by the computer, but still, I would have figured it would just keep it at zero. Probably a little stressful for you as well, glad to made it.

Yeah, thanks. Definitely made it back home the same route with greater ease after knowing where I could charge in between the SC and home (at that RV park). I was pretty sure we would be okay for a short-ish distance past 0% SOC because I've seen YouTube videos where other TESLA owners have driven their TESLA's down to 0% and beyond. My takeaway from those videos was that TESLA definitely keeps a portion of the battery for "reserve", but best not to test that out, IMO.

 

[BitJam]

Kyle Conner demonstrated SoC < 0% in a range test recently. He said there was a 3 kWh buffer.

 

[THEbuz]

Took our first road trip in the 2023 Model Y (LR/AWD), and we barely made it to the first TESLA Supercharger with -4% SOC. (That is correct; NEGATIVE 4% SOC.)

This first TESLA Supercharger location recommended that we charge up to 80% SOC, but I charged a little longer (up to 85% SOC) as a precaution. It was a VERY fast Supercharger @ 250kW, but I could not help but notice that we charged a total of 81kWh (from -4% SOC to 85% SOC). The battery pack is supposedly only 78.1kWh, so, evidently, it is actually larger than that, in reality...??? If we charged 81kWh and the SOC went from -4% to 85%, then the battery pack must be more like 91kWh, no???

CLARIFICATION: My on-screen SOC never dropped below 0%, but the GPS directions that shows your SOC on arrival kept dipping lower and lower, eventually showing and remaining at -4% SOC there in the GPS. My SOC at the top of the screen never went below 0%. Sorry for any confusion; I didn't mean to misspeak on that.

 

[Big Earl]

Kyle Conner demonstrated SoC < 0% in a range test recently. He said there was a 3 kWh buffer.

I wouldn't count on that. One gentleman on this forum recently reported his Y shut down with 4 miles remaining. We have another member whose S100D has a tendency to shut down below 10%.

 

[Goobers]

I wouldn't count on that. One gentleman on this forum recently reported his Y shut down with 4 miles remaining. We have another member whose S100D has a tendency to shut down below 10%.

There was another random YTer that drove around their neighborhood until they ran out of power, it was well below 0.

As for the person with the S100D, I would be more inclined to believe they are an outlier than an indication of the general.

I recently got an adapter cable to connect my bluetooth OBD2 reader (OBLink MX+ which I bought for a previous vehicle) and used "Scan My Tesla" app. It shows an 81 kWH battery with a "nominal" max at 79 kWH.

That said, people really should avoid driving down to less than 10% anyway, as that is bad for the battery. And just in case anyone wants to say something about being able to use all the available power/fuel... ICE isn't much different, if you go too low a number of bad things will happen (fuel pump can overheat, for one).

 

[THEbuz]

I wouldn't count on that. One gentleman on this forum recently reported his Y shut down with 4 miles remaining. We have another member whose S100D has a tendency to shut down below 10%.

Thanks for weighing in. I agree that en masse, we shouldn't count on that. However, in my case with my specific Model Y, I know for a fact how far past 0% I was able to take it, which I wouldn't have otherwise done if I had no other choice. To me, that is validated, but I agree that others should proceed with caution and not assume that their Model Y would do the same thing. I can tell you that my Model Y is a 2023 production build, LR/AWD built in Austin, FWIW. I took delivery in NOV2022.

 

[ChrisMPK]

You know how much you could take it past zero that time. You have no idea what will happen next time you try this. The SOC meter is constantly adjusting. You really shouldn't plan any trips that have you arriving with less than 15%.

 

[ucmndd]

That said, people really should avoid driving down to less than 10% anyway, as that is bad for the battery.

Nah, it’s not.

 

[Iron]

Wondering how you ended up with that dilemma. Did the Nav system not tell you how much you'd have left arriving at each charger? What went wrong? Never took a long trip with mine so truly curious.

 

[hmadsen]

Havent seen anyone comment on it here, but please also remember that you are charged for the power you consume when charging.

The charger is not a lossless device, there will be small losses inside the charger, as it converts the 110/220V AC to 400V DC.

Nothing in this world is free, and that is also true for energy conversion inside of electronics.

When you charge your phone, the wall charger will also be "hot", as there are conversion losses, and the electrical company are also paid for the energy you use to convert, that is converted into heat energy instead of energy put into your phone

 

[HonchoNI]

Add 15-20% on top of the energy added to the battery due to inefficiencies in the conversion. I usually think of 1kw per 1%, which is not accurate, but more accurate than 1kw input per 1kw energy added to battery.

 

[THEbuz]

Wondering how you ended up with that dilemma. Did the Nav system not tell you how much you'd have left arriving at each charger? What went wrong? Never took a long trip with mine so truly curious.

When I input my ultimate destination into the GPS, it directed me to drive 2hrs the wrong way due to SC locations. On the normal route to my destination (when driving an ICE vehicle) the first SC along that route is 254mi from my home. Despite the GPS, I thought I could make it 254mi in my Model Y (LR/AWD) rated at 321mi, but that ended up not being the case. I arrived at an RV park along my route just 45mi before the first SC location with just 3% SOC. I charged up to 15% at 7kW, which took over an hour. We left the RV park @ 15% SOC and arrived at the SC with -4% SOC.

 

[AlanSubie4Life]

we barely made it to the first TESLA Supercharger with -4% SOC.

It doesn’t show negative SOC does it?

My SOC at the top of the screen never went below 0%.

Right.

arrived at the SC with -4% SOC.

Doesn’t sound like you did though.

Seems like around zero percent.

IIUC, the battery capacity below 0% is in addition to this.

That is incorrect. For Model Y/3, the 4.5% buffer (it is always 4.5% of the max) is included in this calculated number from the formula you gave. The formula you gave works great and is correct and matches the BMS unless the car is brand new (in which case the capacity may end up even higher than the calculation).

So usable is 95.5% of this value.

The Model Y LR AWD will end up with 79kWh with this formula when new (may actually be higher), while the Model Y P will give about 80.6kWh with this formula when new. (“When new” means: “showing max EPA range”.)

They both have apparently the same pack and start at similar capacities but this small discrepancy exists.

people really should avoid driving down to less than 10% anyway, as that is bad for the battery

No, it is fine.

You really shouldn't plan any trips that have you arriving with less than 15%.

This is way too conservative. Just make sure you have enough margin to arrive above 5% so you don’t have to worry about nags to slow down. And it is totally fine to aim for quite a low SOC if you are close. If you start a trip with 95% SOC and the estimated arrival charge is 5% - don’t do that. Get some margin, and then drive fast to cut into that margin.

The trip planner is kind of screwed up sometimes so dead reckoning may be a good option in flatter terrain rather than relying on the planner.

Some people seem to have shutdowns above 0% but this is very bad and typically (not sure if always) indicates some pack marginality (according to @wk057 recent statement). The whole purpose of the buffer (which you should not use unless you don’t mind being towed) is to avoid that scenario! It’s supposed to help avoid situations where there may be a couple % BMS error resulting in shutdown.

In the EPA test they drive all the way through this buffer until the car shuts down on the dyno (this is done with a steady state cycle which is quite low power output I think).

 

[THEbuz]

It doesn’t show negative SOC does it?




Right.



Doesn’t sound like you did though.

Seems like around zero percent.



That is incorrect. For Model Y/3, the 4.5% buffer (it is always 4.5% of the max) is included in this calculated number from the formula you gave. The formula you gave works great and is correct and matches the BMS unless the car is brand new (in which case the capacity may end up even higher than the calculation).

So usable is 95.5% of this value.

The Model Y LR AWD will end up with 79kWh with this formula when new (may actually be higher), while the Model Y P will give about 80.6kWh with this formula when new. (“When new” means: “showing max EPA range”.)

They both have apparently the same pack and start at similar capacities but this small discrepancy exists.



No, it is fine.



This is way too conservative. Just make sure you have enough margin to arrive above 5% so you don’t have to worry about nags to slow down. And it is totally fine to aim for quite a low SOC if you are close. If you start a trip with 95% SOC and the estimated arrival charge is 5% - don’t do that. Get some margin, and then drive fast to cut into that margin.

The trip planner is kind of screwed up sometimes so dead reckoning may be a good option in flatter terrain rather than relying on the planner.

Some people seem to have shutdowns above 0% but this is very bad and typically (not sure if always) indicates some pack marginality (according to @wk057 recent statement). The whole purpose of the buffer (which you should not use unless you don’t mind being towed) is to avoid that scenario! It’s supposed to help avoid situations where there may be a couple % BMS error resulting in shutdown.

In the EPA test they drive all the way through this buffer until the car shuts down on the dyno (this is done with a steady state cycle which is quite low power output I think).

The SOC at the top of the screen never dipped below 0% but stayed at zero while I drove another ~15mi or so after it actually hit 0% SOC. The reason I know I was at -4% SOC upon arrival at SC is because the on-screen GPS showed that I would arrive at the SC with -4% SOC, and then my SOC hit 0% approximately 15min from the SC destination.

I charged 81kWh when I arrived at -4% SOC and brought my SOC to about 85%. That means my total battery pack is at least 81kWh.