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Battery reserve and real world range

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My unscientific impression thus far is that in mixed city/suburban driving where the speed never exceeds 50 mph, the S consumes about 285-290 Wh/mile, on average, which means that the actual range will exceed the rated range by a few percent. I'm pretty good about staying off the binders, but the seat of my pants is still tuned to the Roadster's stronger regen braking, so I generally do have to use the friction brakes a little more than I'd like. Still, the stop-and-go range seems pretty impressive.


Started the day with ~240 and gave a few test drives to some friends; it was as I parked at lunchtime that I noticed this:

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Note that Sarasota is flat as a pancake (this isn't from running downhill at all). This comes from driving around the city and coasting with regen up to stop lights. I always have good city mileage in my Roadster, despite showing off when the lights turn green.
 
I'm finding that secondary roads / city driving produce *worse* results than consistent 65 MPH highway driving. ...

Which brings up a point. What is everyone's experience with city driving? The general EV/regen lore is that you should get better mileage than on the highway. I always doubted the EPA 88 city/90 hwy. numbers.
 
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Took another long drive today and got home with 10 miles of range remaining. Went out to dinner and back and I was down to 2 miles. The parking lot behind my building was empty so it seemed like a good time to see what happens when you get down to zero. I cranked the heater up to high and drove around the lot. BTW Tesla is right about the heater using way more juice than the seat heaters. Both seat heaters and rear defrost barely moved the Kw needle but the cabin heater sure did. Anyway I circled the lot until I got to zero and at that point the range indicator in the speedo changed from "1" to "Charge Now". I took a few more laps around the (small) parking lot, nothing else happened. ...

Looking at the screen it shows you used 76.9 kWh, so you started with a standard charge? Otherwise I assume it would have read closer to 85?
 
I took a 400-mile trip yesterday. For about half of it, I had cruise at ~63mph where traffic allowed, and I was getting very close to the EPA-rated range; just a couple of percent below. (Weather was so-so: mid 50's, a small amount of rain so roads were mostly just kind of damp, we were using what seemed to be a tiny amount of heat, and I periodically turned on the front defroster).

For the other half, I had cruise at ~72, and of course range was lower. Maybe 10%? Dang, should have written the numbers down. Overall I think I used 430 miles of range to go 400 miles.

About 2 weeks ago we took a 160-mile trip that went over a mountain pass twice. Weather was better, except it was 42 degrees at the pass so we did use the heater when crossing that. Probably never got over 65mph; in fact for a fair bit we were around 57mph. We got very near the rated range for that trip, too.
 
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That is very encouraging and impressive, Chad! As we both know, that is certainly better than one would get in the Roadster, relative to rated/ideal range, under the same conditions.

Hmm, just read post #17. If your car is "rated" at 265 mi, then this is still pretty good, but not really better than the Roadster, I suppose.

I actually wish that Tesla would offer a firmware upgrade to the Roadster to recalibrate "Ideal Miles" to the 5-cycle test, so those of us with both cars do not have do do all this compensation in our heads all the time! It could be settable as a "Setting" on the VDS, so traditionalists could still have it the old way if they wanted.

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Took another long drive today and got home with 10 miles of range remaining. Went out to dinner and back and I was down to 2 miles. The parking lot behind my building was empty so it seemed like a good time to see what happens when you get down to zero.

Hmmm, interesting. I was wondering how they handled the very low SOC compared with the Roadster. So it looks like they say range is zero at about 5% SOC, like the Roadster does at 10% SOC, but the Roadster annoyingly just says "Range Uncertain" and reports "---" for the range. I think that, based on @vbsdan's experience, the red bar left in the indicator is real capacity, but very limited. As someone who has once had to tow my Roadster up my driveway because it hit "true" zero 100 yards from the garage, it is a good thing you stopped lapping the parking lot when you did! Also be aware that the estimate of remaining SOC can be unstable at very low levels (at least with the Roadster). A number of us have had the experience of squeaking home or to a charge stop on the road, and then watching the range gauge drop 3-5% after a few minutes sitting still, or after cycling the power off and then on. Careful in that red zone!!
 
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I did my first mini-roadtrip of 160 miles roundtrip. Even checked out the new Texas autobahn where the legal speed limit is 85 mph. I should have taken a picture but since I was driving, I didn't. Even at 85 mph I was getting around 380 Wh/mile I believe. On the way home going 70mph it was around 350 Wh/mile.

This car is unbelievably smooth and quite at 85mph. I couldn't believe it.
 
Today I drove my Model S until it was showing two miles of range remaining.

So when you get this low, or even fairly low, I'm assuming that you have to be looking at projected range, right? Given that projected range is almost always somewhere below rated range (a little to a lot below depending on driving habits and other factors), what happens to rated range as you get really low in projected range? Could it still show that you have 100 miles of rated range while projected (and actual) gets down to virtually none? Or do the rated and projected range converge as you approach empty?
 
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On a serious note - driving the car like a performance vehicle will give you a driving range about 70% of the rated range.

And 1/3 to 1/4 of EPA range playing race car driver on a track. :biggrin: See Model S vs Roadster on the Track

At the end of the day, we convinced the track folks to stick around while I accumulated a total of 97 rated miles in the battery for the 82 mile drive back to home. The track and my house are at about the same elevation with only gently rolling hills and valleys in between. Remember to correct elevation changes at 6 mi/1000'. Because the Roadster accumulated many more miles on another RV plug (same charging power, fewer Wh/mi) while we waited, and it was after dark, I had my friend drive my Roadster behind me with the flashers on as I started a very conservative drive home.

While charging, I looked up RV parks between the track and my house on my iPhone. There were 6 and I called them all. A KOA nearby answered, but had just reserved their last 50 Amp spot, 4 did not answer, and one RV park hung up on me when I mentioned electric car. :frown: I was on my own with 15 spare, rated miles.

I started the drive very conservatively on cruise control at 47 mph. As I drove through the dark, I decided my rules to get me home with a high confidence were to keep a 20-25% reserve of rated miles with a minimum of 10 reserve miles. Following that rule, I slowly increased the speed up to 55 mph halfway home. As I got into central Denver, I was able to resume a moderate driving style, transitioning to aggressive for the last 10 miles. I parked in my garage with 9 rated miles left!
 
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.... As I drove through the dark, I decided my rules to get me home with a high confidence were to keep a 20-25% reserve of rated miles with a minimum of 10 reserve miles. Following that rule, I slowly increased the speed up to 55 mph halfway home. As I got into central Denver, I was able to resume a moderate driving style, transitioning to aggressive for the last 10 miles. I parked in my garage with 9 rated miles left!

Great technique and information! This is exactly the kind of strategy ("conserve early, then spend when you've got it make") that I use in jet flying.

My first trip as pilot to Hawaii (6 hours over water) I asked an experienced airline pilot how much fuel reserve we will have on landing. His answer: exactly what you plan! Why: because you will slow down on the first few hours until you have your predicted planned reserve "made" plus some, then power up and go as fast as you can to land with just what you planned.

Works great!