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Does this make sense? Fall day in a 70D

David29

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Aug 1, 2015
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Does this make sense?

I have had my Model S 70D for six years, so you would think that I understand how the battery operates in cool or cold weather. But a couple of days ago, I had an experience that makes me think it has either degraded, or I have forgotten how tough cold weather can be.

Here is how the afternoon went, as I remember it.

It was chilly overnight, with low temps in the 30s (F). My car is always parked outside, and I did not have the charging set for preconditioning. The battery was recharged by about 20-25%. In the morning, I only ran one short errand, so the battery was not warmed up by early afternoon, and regenerative braking was very restricted. The air temp by then was in the mid-40s. We made a trip of 13 miles, about 4 miles at freeway speeds and the rest at 30-40 mph. That trip did not result in much change in the restriction of regenerative braking, if any.

We stopped to see a grandkid’s basketball game, so we were there close to an hour. The next leg of our trip was 35 miles, nearly all highway, at freeway speeds, where we stopped at a supercharger. I noticed that the heater seemed to be struggling to keep the cabin warm. It just did not feel as warm as the setting called for. I was surprised that the regen limit did not disappear by the time we arrived. The battery SOC was somewhere around 40%, I think, not very low but we needed some charge to finish our trip and to get back home. Our charge rate was only around 28 kW when I checked it. I thought that was ridiculously low, probably because the battery was cold and it needed to warm up.

Key question -- Shouldn’t 35 miles at 70 mph have heated up the battery enough to get a decent charge rate?

After we charged for a while, the battery was up to about 65 or 70%, I think, and we left. Now the regen limit was gone and the heater worked well, noticeably better.

Our next trip was another 13 miles. We were at that location for a good hour, and then returned home, a distance of 55 miles. During this last leg, the heater worked fine and we had no regen limit for the entire trip.

So, does this make sense? It seems as if the regen limit should have disappeared before the stop to supercharge, and that we should have gotten a better charge rate. And the car heater should not have struggled to keep the cabin warm when the air temp is in the mid-40s. We had plenty of charge. If we were having this behavior at 45F, I dread to think what it will take to drive in real winter weather with temps below freezing! It could be my memory is poor and that this is typical of fall weather, but it seemed worse than I recall from previous years. We got no warning messages, so I doubt there was anything seriously wrong with the heater or the battery heating, but still...

There was another anomaly, too. When we got to our next-to-last destination, the trip data showed we had averaged about 325 Wh/mile, which seemed about right for the speeds and temperatures we were in. But when we came back out, I looked at the energy app, and it said we had averaged only 290 Wh/mi for the last 30 miles! That made no sense. I looked again at the trip data, and it had changed to the lower amount. It does not make sense that we would have gotten efficiency of 290 Wh/mi on a cold fall day at highway speeds! I seem to recall someone posting about erroneous trip data a few weeks back, but this is the first time I have noticed it.

It could be this is perfectly normal and I am in denial about past years, but it did not seem normal.
 

DerbyDave

Active Member
Jul 2, 2020
1,761
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Kentucky
Perhaps your coolant needs to be changed? There used to be scheduled maintenance for this, I believe it was 4 years. Now there is no specified change interval, but the car is out of warranty, so Tesla probably doesn't care. It is now lifetime coolant.
 

ucmndd

Well-Known Member
Mar 10, 2016
7,707
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California
Do you have range mode enabled without realizing it? That would help explain the lackluster HVAC and slow battery heating.

As for the key question - “Shouldn’t 35 miles at 70 mph have heated up the battery enough to get a decent charge rate?”

My observation is a resounding “no”. Steady-state freeway cruising in cold weather does not do a whole lot to heat the battery.
 

Tam

Well-Known Member
Nov 25, 2012
10,121
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Visalia, CA
My observation is a resounding “no”. Steady-state freeway cruising in cold weather does not do a whole lot to heat the battery.

Older Tesla still has a traditional heater for its own battery so, in theory, 35 miles at 70 MPH should do it.

I think the issues here might be related to the age of the battery. I think a battery replacement would help out all the numbers cited.
 

ucmndd

Well-Known Member
Mar 10, 2016
7,707
14,991
California
Older Tesla still has a traditional heater for its own battery so, in theory, 35 miles at 70 MPH should do it.
My "older Tesla" experience says otherwise. In fact, I regularly conduct a very similar trip to what OP describes, About 30 miles at freeway speeds with a cold-soaked battery in the 30-40 degree Central Valley mornings to a supercharger. If I don't navigate to the supercharger so the battery can precondition and actually use that "traditional heater" you mention, I definitely experience reduced charging speeds. Driving there alone doesn't cut it.


I think the issues here might be related to the age of the battery. I think a battery replacement would help out all the numbers cited.
lol, of course if would, but "hey, just go ahead and spend $20k to fix it" isn't a reasonable or useful solution to most people.
 
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ucmndd

Well-Known Member
Mar 10, 2016
7,707
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California
I can't comment on the battery anomalies, however, I do recommend using the heated seats rather than the cabin heater in cold weather. YMMV
This is completely unrelated to anything in this thread, but fun fact, I just noticed you have exactly as many posts as likes.

Screen Shot 2021-11-22 at 8.21.20 PM.png
 
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David29

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Aug 1, 2015
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@David29 : just to confirm: did you navigate to the SuC (which should trigger battery warming) ?
Yes, I did. Good point. All the more reason why I am surprised we got such a wretchedly low charge rate. Or maybe that is a "normal" rate at 40% SOC in a battery with 55,000 miles on it these days....? I guess i will have to go back to keeping more careful records, as i tried to do when the car was new. I have been rather casual about recording details like this in recent years.
 
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David29

Active Member
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Aug 1, 2015
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DEDHAM, MA
Perhaps your coolant needs to be changed? There used to be scheduled maintenance for this, I believe it was 4 years. Now there is no specified change interval, but the car is out of warranty, so Tesla probably doesn't care. It is now lifetime coolant.
Interesting. No idea. I did bring it in for annual service (brakes and so on), but no mention was made of coolant.
 

David29

Active Member
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Aug 1, 2015
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DEDHAM, MA
Do you have range mode enabled without realizing it? That would help explain the lackluster HVAC and slow battery heating.

As for the key question - “Shouldn’t 35 miles at 70 mph have heated up the battery enough to get a decent charge rate?”

My observation is a resounding “no”. Steady-state freeway cruising in cold weather does not do a whole lot to heat the battery.
I'll check that. I have rarely ever used Range mode, but just perhaps....
 

David29

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Aug 1, 2015
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DEDHAM, MA
I can't comment on the battery anomalies, however, I do recommend using the heated seats rather than the cabin heater in cold weather. YMMV
I would, but I have an after-market seat cushion because i have a bad back and the Tesla seats are not comfortable for me, so I normally can't take advantage of the heater. My spouse does, though. Good reminder, though.
 
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AustinP

Active Member
Apr 6, 2015
1,405
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Belgium
Yes, I did. Good point. All the more reason why I am surprised we got such a wretchedly low charge rate. Or maybe that is a "normal" rate at 40% SOC in a battery with 55,000 miles on it these days....? I guess i will have to go back to keeping more careful records, as i tried to do when the car was new. I have been rather casual about recording details like this in recent years.
My 2015 85 SuC charge curve (nerfed like yours I guess) equates to "%SoC + kW = +/-100". So at 40%, I'll see around 60kW (if battery warm indeed)
 

Rocky_H

Well-Known Member
Feb 19, 2015
7,321
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Boise, ID
I'll check that. I have rarely ever used Range mode, but just perhaps....
Both of those symptoms sounded to me like Range Mode turned on as I was reading your post before even getting to any of the comments. It will not turn on the battery heater much, and it will restrict the power of the heating system quite a bit. I find it's not very useful most of the time, so I keep it turned off too. But yeah, maybe it got accidentally enabled by some software update. It wouldn't be the first time a setting like that got changed by an update.
 
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I have a Model S75D with 61K miles. Battery degradation from when new is about -10%. Ive never used range mode. can I expect an increase in range if I do? If so do you have any idea what percentage increase is typical. Also, if I take it out of range mode say 20 miles from arriving at the SC will that activate battery conditioning? Thanks,
 

David29

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Aug 1, 2015
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Both of those symptoms sounded to me like Range Mode turned on as I was reading your post before even getting to any of the comments. It will not turn on the battery heater much, and it will restrict the power of the heating system quite a bit. I find it's not very useful most of the time, so I keep it turned off too. But yeah, maybe it got accidentally enabled by some software update. It wouldn't be the first time a setting like that got changed by an update.
I did check later, and no, Range Mode was not on.

Sounds like I need to do some more testing, or at least to take some notes the next time I do a similar trip in similar weather.
 

FlatSix911

Porsche 918 Hybrid
Jun 15, 2015
7,206
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Silicon Valley
I did check later, and no, Range Mode was not on.

Sounds like I need to do some more testing, or at least to take some notes the next time I do a similar trip in similar weather.
Hi David, have you considered using a Tesla tracking app for more detaileded information on energy usage trends and history.

 
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David29

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Aug 1, 2015
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DEDHAM, MA
Hi David, have you considered using a Tesla tracking app for more detaileded information on energy usage trends and history.

Sounds good. But is it only for Apple phones? it mentions the Apple app store but not the Google Play Store for Android.
 

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