Real Prime Battery Capacities

Toyota app sucks in so many ways that I don't know where to begin with.

For Gen 4, the battery-SOC readings are fairly random.

The app stalls and has connectivity issues.

 

4.6 mi/kWh = 155 mpge (multiply by 33.705 kWh/ge), which is reasonable. On Gen 4, the eco diary on the display shows mi/kWh.

Level-2-charging loss should be about 4–5%.

 

What is 7.21? Is it mi/kWh? Is it kWh? Where is it shown and what is it claimed to be?

If it is kWh, it is perhaps the kWh output of the battery during a 24-hour window. Eco diary on Gen 4 shows mi/kWh on a 24-hour window. Perhaps in your case, it is also showing the miles driven and kWh.

And, no, the Toyota app does not show how much kWh goes into the total mechanical dissipative drag force on the car (by drivetrain, tires, and air)—there is no easy way to estimate it. EPA estimates through models run in the field and then on a dynamometer. So, if you are looking for a place to find the overall electromechanical efficiency of the system, you won't find it.

 

Oh no, you do not. Regenerative braking is of course naturally included in the mi/kWh on the display. You have never used the eco diary on your Gen 4?

The BEV charging capacity is 11.7 kWh. That gives 11.1 kWh on what is actually stored in the battery if you assume a 5% Level-2-charging loss on the charger and battery fan, which is probably about right. But then, who cares on what is exactly stored in the battery? You are paying for what you exactly put in from the wall outlet, not what is exactly stored in the battery.

By the way, 10.9 kWh given by Car and Driver, which is incorrect (should be 11.7 kWh), is the Level-2-wall-outlet-meter kWh. They give 6.2 kWh for Gen 4, which is approximately correct. (The true value for a new Gen 4 battery is more like 6.34 kWh.) The Car and Driver blog has no means of measuring what is actually stored in the battery.

 

That’s right regen is included on the data screen, of course. Thats what I said. So it is subtracted out of the 52x4.6 for useable capacity after charging without using the car. The mpg figures are based on driving tests. But miles driven in an ev include regen. Gas cars don’t get added gas during the epa tests, but ev cars can’t avoid adding electrons to the battery during testing due to regen.
When they say 25 miles in gen 4 this includes regen, yes or no. So if it does include regen 25 can’t be used in the calculation, right? Energy was added. If it doesn’t include regen well that’s a strange way to tell the public how far their car can go, because in ev there is always regen in a driving cycle.
I am just trying to dig a little deeper, as Toyota would keep more buffer than 2 kwh imo. 3 would still not be much divided top and bottom. 3 would leave 10.6 on the battery useable capacity.

 

Regenerative braking is always hidden/included in every mpge and kWh figure, and you never subtract it. It is pretty huge in city driving by the way, like 50% of the energy. That is why hybrids have twice the fuel efficiency of nonhybrids in city driving. Without regenerative braking, you would only get about half the BEV range in the city, like twelve miles.

 

If the goal is to find out the useable battery capacity, I don’t know why regen wouldn’t be subtracted. They don’t add gas when testing gas cars.
Also I know about hybrid reasons for increased fuel efficiency having bought a new 2007 Prius for those reasons.

 

On more sober (literally--it was Saturday night) reflection, I believe I was correct the first time, you shouldn't remove regeneration from the equation. If you do a lot of regen, then the kw/m goes up, and so does the actual EV range. Just as if you do a lot of regen and EV usage in HV mode, the MPG and range go up. We don't rate the Prius at 25MPG because the other 25 is on the electric motor courtesy of regenerative charging. We rate it 50mpg.

It's the amount that the Toyota App shows a full recharge being, which is obviously wrong because you're putting 11.6 into the vehicle per the charger not to mention the cars range is too high for it to be only 7.21kw. But I can't stop wondering where the hell Toyota is getting that number from.

 

Accounting for regenerative braking would neither help you nor is needed in determining the kWh stored in the battery vs. kWh put into the charger or the kWh output from the battery. You can easily measure the actual input and output currents from the battery with ammeters or calibrated current sensors and determine all these values in that way. There is no other precise way.

The way the EPA testing is as follows. First, the vehicle is coasted down with no power applied from the drivetrain in the field. That helps you determine the air drag as a function of speed by plotting acceleration vs. speed. Drag force is acceleration times mass (Newton's second law). Then, the dynamometer in a laboratory is calibrated with the same coast-down acceleration without drivetrain power as a function of speed so that the air drag vs. speed is accounted for. Once the dynamometer is calibrated to account for air drag as a function of speed, vehicle is run with its own power at a precise test-driving pattern to determine the gallons of fuel or kWh of electricity used. None of this is exact science but all is an approximation.

There is no way to precisely separate the various energy gains or losses during the EPA tests. As I said, the only way to know what is going on inside the battery is to use ammeters in the battery input and output.

 

Exactly! Regenerative braking has nothing to do with useable battery capacity or charging capacity. In principle, you can turn regenerative braking on or off, which would change the fuel efficiency and driving range, but it would not change the useable battery capacity. In fact, the battery doesn't even have to be installed in the vehicle to determine the charging capacity or useable battery capacity.

I just looked at my Toyota app and all kWh values exactly correspond to 6.3 kWh @ 100% SOC, which is the same as the 6.34-kWh charging capacity obtained from the EPA equation I provided here. Note that the kWh in the app is not measured but calculated from the SOC change, as each value corresponds to exactly 6.3 kWh @ 100% SOC. So, the app database lists 6.3 kWh for Gen 4 Prius Prime, and that's what the app uses to calculate the kWh from the SOC change. Yours should work, too. Update to the latest version of the app and make sure that you are scaling the kWh to 100% SOC. If you are still getting the wrong capacity, contact Toyota to have the app database corrected for Gen 5 Prius Prime. The correct capacity for Gen 5 Prius Prime is about 11.5–11.7 kWh according to EPA as I explained here.

 

Of course the useable battery capacity is some specific value that starts with a full battery after charging. The second the car is driven and slowed down, bye bye original useable state of charge value. More energy added. Temp also plays a factor I read, but you know what, all one needs to do in a Prius is drive. I often use B to increase regen but it has a perfect normal feel regen without B and I see no button to turn it off. It’s got pretty strong regen without B. EPA “coasting” is regenerating. That extra has to be subtracted to get the original useable charge.
How long will this go on here, months? I think I have said it clear enough. One more answer from you which says no you’re wrong, no way, and it’s done, ok? Fine.
I did a 2014 Volt and the calc is too high for useable charge. So this left questions.

 

No, there is no regenerative braking during EPA coast-down because the vehicle is put into neutral. It is not a coast-down if the vehicle is braking—frictionally or regeneratively. Coast-down means the vehicle is in neutral gear without braking of any sort.

 

What you calculate from the EPA formula I gave here is the charging capacity using a certain EVSE read at the wall kWh meter. For 2014 Volt, the EPA formula gives 13.1 kWh. Back in 2014, chargers were less efficient. On top of that, perhaps EPA used Level-1 charging, which is less efficient than Level-2 charging. If it is actually 10.9 kWh stored in the battery, then it is a 17% loss for an older Level-1 charger, which sounds about right. For Gen 4 Prius Prime, Level-1 charging loss is about 14%. However, a modern Level-2 charger has a loss of only about 4–5%. Good DC charging is over 99%-efficient in the vehicle, as there is no AC/DC conversion. In any case, people are not interested in what is actually stored in the battery, but they are interested in how many kWh they are being charged for (no pun intended) on their wall kWh meter.

It is a misconception that you need to subtract regenerative braking to calculate useable battery capacity, which makes me think that the concepts of kinetic energy and energy conservation (first law of thermodynamics) are not understood, as regenerative braking does not actually generate energy but recycles the energy that already came out from the battery back and forth between the battery and motor–generator. It is also a misconception that the EPA coast-down has regenerative braking, while in reality it is done in neutral gear to estimate the aerodynamic drag, not regenerative braking.

 

Reclaiming, recycling, it’s all energy added back into the battery. You don’t add gas in the epa tests, and reclaim, or add, energy. Reclaim=add, recycle=add.
I stick with 10.6 kwh as my guesstimate. That’s my bet. Pretty low buffer at 3 I would say, even at 10.6. I see no misconceptions in anything I said. I lasted pretty good not replying but sometimes it just has to go there when personal stuff is said. It’s your opinion, and I have mine that’s it.

 

What matters is the kWh at the meter. Car and Driver got the kWh at the meter wrong—it is 11.5–11.7 kWh, not 10.9 kWh—and I corrected it in my first post in this thread.

As for the actual kWh stored in the battery, assuming a 5% drop on the Level-2 charger from 11.5–11.7 kWh at the meter, it would be 10.9–11.1 kWh. Your value is about 0.5-kWh-lower, but that's not a very large amount. The exact value will be speculation on everyone's part because we have no data for it. If you are right and the Toyota charger is less than 95%-efficient, then you guessed it right, which is not good for the owners, as they would be paying more at the plug than they should.

I don't think you understand the concepts of inertia and energy conservation. Inertia is programmed into the dynamometer in EPA testing as F = ma (Newton's second law), as the vehicle itself has no inertia because it is stopped in the laboratory. That programmed inertia causes the battery being discharged during acceleration (positive acceleration a) and being charged through regenerative braking during deceleration (negative acceleration a). Regenerative braking is not added or subtracted in the mpge results—mpge is directly calculated from the kWh meter at the plug and miles on the odometer. Of course an EV is more efficient than a non-EV thanks to regenerative braking, but that's one of the great things about EVs. There is nothing personal here—I am a physicist and know the laws of physics well, and it gets my attention when someone tries to turn the laws of physics upside down. What is confusing you on regenerative braking, and perhaps I could explain it?

@Numtini, have you checked your SOC and kWh numbers in your Toyota app? Could you share a screenshot?

 

Certainly. The 30%->100% for 7.21kw are "empty" to full. The public one was measured by Chargepoint at 11.65kw. So something is definitely not right.

 

If you scale it to 100%, you get 10.3 kWh for every charge shown in the history. For example, (100% / 70%) × 7.21 kWh = 10.3 kWh etc. This means that the app assumes that 100% SOC corresponds to 10.3 kWh. Note that the app only measures SOC, and it does not actually measure kWh but calculates it from SOC.

For Gen 4, the app assumes 6.3 kWh for 100% SOC, which is what you get at ChargePoint as well as what you get from the EPA formula. EPA formula for Gen 5 gives 11.5–11.7 kWh, and you said that you got 11.65 kWh at ChargePoint. So, I don't know why the app is not agreeing here. I would say, try ChargePoint again from 0% to 100% and see what happens. Also, if EPA used Level-1 charging, it would be a higher kWh, but they say 4 hours; so, it should be Level-2 charging.

 

edit: dang, I missed the whole last page of this discussion.

One of the reasons the app shows different numbers from some of the the dash displays is that the app is not optimized to the Prius. It's got a wide range of Toyota vehicles it supports. The same is true to one degree or another for any app that supports a wide range of hardware that are not always programmed the same.

The key that I take from mismatched data points is, know at very least the top and bottom differences as soon as possible in real world application, than detect over time if the full range of difference is linear, curved, or something else..

continued from edit at the top: I hope this post makes sense to someone else, anyone else, beside me. lol

 

All the app does is to scale the SOC according to the official EPA kWh for 100% SOC at the 240-V plug, which is 11.6 kWh.

So, if you charge from 50–100% SOC, it will show 11.6 kWh / 2 = 5.8 kWh.

[2023 Prime] Watts, Watt-Meter, and Not What | PriusChat

PS: Apparently, they corrected the EPA kWh for 100% SOC at the 240-V plug in the app, which was previously being shown as 10.3 kWh. 11.6 kWh for 100% SOC at the 240-V plug is the correct value.

 

That’s what my math suggests too.

I can’t stand this calculation because 100% in the app is 100% in the car, but all of the rest of the values are off for no reason other than this scaling. But the range of the EV is pulled directly from the car’s estimate. So theoretically they could have done the same thing with the state of charge estimate.