Daily charging

No, I can see on the graph it drew electricity 4 times long after completion. A full recharge for my Prime is only 5.75 kWh and I may have had a little electricity still when I plugged in.

 

So, the graph on the bottom is for the actual draw since the completion of the charge on 12/24 at 3:34 PM?
If that is correct then 4 draws correspond to
12/25 0:00AM
12/27 10:00AM
12/28 4:00AM
12/29 unknown time

Since the graph does not show the last 12:00AM marking, I can't tell when the last draw happened. But it seems to be on 12/29 assuming that the first 12:00AM is marking is 12/25 0 AM (midnight). If this interpretation is correct, then the car is drawing electricity, presumably for the traction heater function, somewhat randomly about once a day even after 3days past the completion of the charging.

That means there is no switching off the traction battery heater functioning after 3 days. But that still leaves the question of what purpose this function is serving? Is it better to keep the charging cord plugged in the extreme cold even if it risks draining the 12v battery or should it be unplugged sooner?

 

I was able to drive to get dinner with electricity, despite the cold... which i captured a photo of.

 

So, do you think if it was not kept plugged in, the car would have started the engine upon the staring due to the cold soaked battery and inability for the car to use the heat pump? Did you have the heat ON when you started the car?

From my experience, even if the car is plugged in overnight and still plugged in until right before the departure, the engine would start on a cold morning as soon as I start the car with the heater ON. If the heat was kept OFF at the time when the car is turned on, then even at extreme cold down to single-digit F, the car starts and can be driven on 100% EV mode. I think this is true regardless of the car having been plugged in for longer than 3 days or kept unplugged after charging. So, I really don't see the benefit of spending extra electricity to keep the battery warm after the change was completed.

 

That misses the point. Think about why BEV also have a battery-heating system, despite not having a gas-engine. It is because the chemistry of the battery takes an efficiency hit when temperatures are below freezing. Electrical resistance within increases quite a bit. To avoid that penalty, the battery is warmed. Ideally, it is above 10°C (50°F).

There is a secondary benefit to warming the battery. To enable super-charging (those really fast DCFC speeds), the battery must be warmed quite a bit. Ideally, it is above 50°C (122°F).

 

I think heating the battery in the Prime is “good practice” for its maintenance in extreme cold but is not essential to the overall functionality of the car. For a BEV, it’s vital.

 

So, are you saying that prewarming traction battery by the battery heater plugged into the wall for more than 3 days using 1.51kWh of electricity (7.26kWh - 5.75kWh by your own stated numbers) performed better than cold-soaked traction battery? Have you ever been able to show the efficiency difference in miles/kWh on battery heated vs cold-soaked? If the efficiency difference is not more than what you spent on heating the battery, then again you are wasting the kWh needlessly.

The notion of enabling super-charging is total nonsense for our discussion. Our PP is not equipped with a fast charger.

 

Purpose of our discussion is to educate about plug-in benefits. Omitting information intentionally would be cherry-picking. Remember, Toyota's underlying purpose of Prius Prime was to gain real-world EV experience that could be applied to the rest of the fleet. That is why high-volume sales were not a priority. To spread a sampling of data-collection opportunity across a wide variety of owners has been achieved. If you look at the cold-temperature system in RAV4 Prime, you can see how that knowledge gained was already applied. With the upcoming bZ4X, having experience already is priceless. Look up feedback related to LFP batteries from owners in China for perspective.

As for your question, there is simply no way to perform such a comparison. There are too many variables at play... more so than the margin-of-error would inform. Statistically, it is a moot point for some anyway. During my 5.5 years of ownership, that was the first time the car has remained unused for that long while not on vacation.

With regard to needless waste, what about pre-warming the vehicle just prior to driving? That may give you more bang for the buck. It is an option which should be part of this discussion.

 

OK, I was just hoping to see real evidence that the traction battery heater has some benefit other than wasting electricity. It is one of the features along with the battery cooler function, that Toyota slapped onto PP without much explanation as to what function it serves. If it is an essential functioning part of the battery management, I would think Toyota will not let the owner to turn this feature on and off. The fact that the battery heater feature can be turned off is the most puzzling part.

If you are asking my opinion on that subject, then I think the PP's climate pre-conditioning feature is a total waste and an utterly useless feature of the car. I tried using it several times back in 2017 when I first got PP, but very quickly realized that it serves no useful function for my needs and use case. I have not used that feature ever since. This goes the same for the Remote Climate functionality either by a fob or via phone app.

 

I was wondering if you would ask for detail in one regard and dismiss anecdotally in another, since it it a super easy trap to fall into.

 

Not exactly sure what you are trying to say here. But if you are asking me why ask questions about the traction heater and not about the climate pre-conditioning, then here it is...

I used climate preconditioning, experimented with it, and tested its functionality for my needs, and concluded that it serves absolutely no function for my needs and my use cases. I was able to experiment with the feature since I know for what it is being used and what function it is supposed to serve. With the traction battery heater, I do not know what function or benefit it is providing other than the basic fact that it turns on when the car is plugged and it uses electricity (presumably to heat the battery, but I have not confirmed this myself). Since I don't know what it is used for, I can't even conduct meaningful experiments, thus asking questions to other members that may shed a light on this mysterious feature.

 

OK, as an experiment, I just switched off the Traction Battery Heater feature to OFF on my PP. I always kept this switch to ON for all my three PPs I have owned. We are expecting an arctic blast bringing the low temp to sub-zero next week. I will report if I see or feel any changes in the way my PP operates. For sure, it should use less kWh per charge but may take longer to finish charging due to the inability to heat the battery pack quickly.

 

It will still use kWh to warm up the pack prior to charging. An anecdotal "feel" assessment won't tell us how much extra kWh was consumed later due to cold-battery inefficiencies.

 

Here is an example of what happens to an extremely cold battery-pack prior to charging. Notice how it drew electricity several times before starting the actual charging.

 

And here's a better layout of that graph.

 

True. But it also goes another way as well, as you said it is also impossible to tell how much kWh was saved due to warmed-battery efficiency by having the Traction Battery Heater option ON. With my experiment, at least I can document how much less kWh is consumed from the wall during a regular charge session on cold days without the Traction Heater ON. I plan to keep the Battery Heater OFF for the month of JAN and compare it with Dec when I had the Battery Heater ON.

If the Heater OFF has no perceivable effect on the overall efficiency and performance of the car, but the amount of kWh saved from the wall is large enough, then I will probably keep this option OFF from now on. On the other hand, if the Heat OFF shows obviously perceivable loss of efficiency and/or performance, then I will likely turn the option back ON.

If the Battery Heater is always beneficial or required for battery management, then Toyota would not give an owner a choice to turn this on and off. The fact this feature is owner selectable tells me that it is not necessary. I am still not sure what this feature's function and merit are.

 

Why do all that to save a trivial amount of electricity? It's just another form of hypermiling few will ever care to follow. A back-of-the-napkin estimate is you'd spend about $20 for the entire season.

Put into perspective, that is just a single DCFC charging session or roughly 4 full sessions on a public level-2.

 

So, why do people hypermile? Saving may not be the ultimate goal. It is just fun to experiment. With regard to the battery heater, Toyota makes no specific recommendation to use this feature, other than the fact that this feature exists and can be turned on or off. I am just curious to find out why this feature exists.

 

Know your audience. The "people" that do are enthusiasts, not ordinary consumers. As an enthusiast, indulge yourself. That can be a very rewarding & informative experience. You see the data I provide. Mainstream shoppers couldn't care less. We do though, here... as a group of those seeking detail well beyond what most owners ever learn about their own vehicle.

Go for it. Let us know what you discover.

 

Agreed. This topic would not even get a single response if I posted in a "Mainstream shoppers" forum. LOL