Range Loss Over Time, What Can Be Expected, Efficiency, How to Maintain Battery Health

[3sr+buyer]

When the eventual day comes I decide to move on from this car, I will probably change my charging habits away from an "80% every day" strategy.

For an NCA battery, it is likely that the optimal battery preservation charging method for daily use is something like:

• Charge to finish shortly before you start driving.
• Set the target charge to B + D, where B is your safety buffer to avoid running out completely, and D is the amount you use that day. For example, if your B = 10% and D = 45%, set the target charge to 55%. If B + D < 50%, then set the target to 50%, since that is the lowest allowed.

For an LFP battery, the above should theoretically be optimal for battery preservation, but could run the risk of running out completely due to the BMS potentially getting inaccurate, and the lesser rate of capacity loss of LFP batteries makes it less necessary. However, if using the above method with an LFP battery, it is probably a good idea to use a significantly higher B value to reduce the risk of running out completely due to BMS inaccuracy, as well as occasionally charging to 100% to resync the BMS.

 

[Steve446]

You can see from the graph that the Projected Range really took a nosedive last summer. Is this coincident with the onset of warmer weather? Is the same thing happening this year? Notice the recent step down.

My car also shares a garage with an ICE. It's not vented to the outside and it gets HOT in there during the summer months.

When the eventual day comes I decide to move on from this car, I will probably change my charging habits away from an "80% every day" strategy.

I tend to agree with @AAKEE post #5096. So, actually, if you look at the trend rather than absolute values then it appears that the downwards slope started at or around 2021-01 (draw a straight line downwards from 2021-01 to at least 2022-06). IMO you can even go back to 2020-03 with the same slope... Ignore the odd ups and downs as @AAKEE suggests. Also, did anything change around 2021-01 regards your car?

 

[andy92782]

I tend to agree with @AAKEE post #5096. So, actually, if you look at the trend rather than absolute values then it appears that the downwards slope started at or around 2021-01 (draw a straight line downwards from 2021-01 to at least 2022-06). IMO you can even go back to 2020-03 with the same slope... Ignore the odd ups and downs as @AAKEE suggests. Also, did anything change around 2021-01 regards your car?

Nothing noteworthy I can think of. The only interesting part of the graph from a driving perspective happened in 2020-03 when mileage accumulation dropped off. That was the beginning of the pandemic.

 

[AAKEE]

For an …

Very good post, you did your homework

 

[3sr+buyer]

Very good post, you did your homework

Of course, probably what a lot of people really want to know is how much of a difference in battery life different charging methods make in actual cars (as opposed to cells in a lab that may not be identical in behavior to those in a car).

 

[andy92782]

Current stats:

2018 LRAWD with 19s (10/18 build)
~27.5K on the odometer
260 Wh/mi lifetime (trip computer)
SoCal (not cold)
80% daily charging for much of its life w/ infrequent Supercharger visits (<1x/mo over the car's lifetime).

Current 100% estimated range is ~268. I'm changing my routine away from daily charging and trying the BMS calibration procedure outlined in this post to see if it helps recover any range although I'm not terribly optimistic it will.

I've used Teslamate to track data for the past ~2.5 years. Here's a chart showing predicted range vs. odometer since I started using it:

View attachment 828173

Quick update: I stopped charging the car to 80% every day. Lo and behold, Projected Range is starting to creep back up:

 

[Apprunner]

Quick update: I stopped charging the car to 80% every day. Lo and behold, Projected Range is starting to creep back up:
View attachment 829576

View attachment 829578

Projected range doesn't have much to do with your max daily charge. Just means your BMS is making its best guess with this change in your routine. Your battery is the same as it was prior to this change. The only thing that changes now due to your process change is that your car has an average lower SoC which slows down battery degradation from this point on.

 

[andy92782]

The only thing that changes now due to your process change is that your car has an average lower SoC which slows down battery degradation from this point on.

That is not the only change that's happening as a result of the new routine. The other change is that the BMS is doing a better job of estimating 100% range, which, as I hoped, is starting to move upwards. I'm well aware that the battery itself is not magically increasing in overall storage capacity. That would be physically impossible.

 

[Apprunner]

That is not the only change that's happening as a result of the new routine. The other change is that the BMS is doing a better job of estimating 100% range, which, as I hoped, is starting to move upwards. I'm well aware that the battery itself is not magically increasing in overall storage capacity. That would be physically impossible.

I don't know if I agree with that assumption of the BMW doing a better job. I think its doing the best it can all the time and the only way its truly more accurate is when you calibrate it by getting the battery to a low SoC and letting it sit there to adjust and then charging it to 100% to retrain the BMS. Is there any evidence that not charging everyday to 80% yields in a more accurate BMS over time?

 

[andy92782]

I don't know if I agree with that assumption of the BMW doing a better job. I think its doing the best it can all the time and the only way its truly more accurate is when you calibrate it by getting the battery to a low SoC and letting it sit there to adjust and then charging it to 100% to retrain the BMS. Is there any evidence that not charging everyday to 80% yields in a more accurate BMS over time?

When I charge to 80% daily, the car almost never falls (and stays) asleep at any other charge level. The BMS had very few opportunities to calibrate itself at lower (or higher) states of charge.

 

[Andy Do]

Did my first road trip today and the range was terrible. I was surprised to see 73% for only 169 miles. That’s approximately 232 miles full range. This is with 40lbs lighter after market 19” wheels. The ride was 95% highway and I was using Autopilot most of the ride. I actually got there with less than the estimated percentage. I know the advertised 315 miles is not accurate but more than 25% less is just ridiculous.

This combined with slow peak-hour super charging made the Tesla more expensive and a lot more time consuming than an efficient ICE.

 

[Andy Do]

Welp. Looks like 85mph is the culprit. I was really hoping for at least around 270-280, but unless I drive 60-70 mph, I’m stuck with <250.

 

[AlanSubie4Life]

Welp. Looks like 85mph is the culprit. I was really hoping for at least around 270-280, but unless I drive 60-70 mph, I’m stuck with <250.

Yes, this is normal. Going over a couple hundred miles between charges is rare on a road trip. First leg it can happen but beyond that it is unlikely.

All can be calculated. You were getting about 330Wh/mi. You need to get about 242Wh/mi indicated on the trip meter to get 315 miles from 100% (at 315 rated miles) to 0 rated miles, assuming you have a brand new car with no capacity loss.

Your after market lighter wheels are likely marginally hurting your efficiency to the extent they are less aerodynamic than stock (the weight does not matter; it has negligible impact on this sort of drive). However, depending on the tires you have, they could be slightly better than the 20” tires (though they really are not bad). Hard to say. Aero probably worse but rolling resistance might be better.

 

[3sr+buyer]

Did my first road trip today and the range was terrible. I was surprised to see 73% for only 169 miles. That’s approximately 232 miles full range. This is with 40lbs lighter after market 19” wheels. The ride was 95% highway and I was using Autopilot most of the ride. I actually got there with less than the estimated percentage. I know the advertised 315 miles is not accurate but more than 25% less is just ridiculous.

This combined with slow peak-hour super charging made the Tesla more expensive and a lot more time consuming than an efficient ICE.

View attachment 829654

85mph will greatly worsen economy and range.

Blasting the AC in 105F weather doesn't help either.

 

[Andy Do]

Yes, this is normal. Going over a couple hundred miles between charges is rare on a road trip. First leg it can happen but beyond that it is unlikely.

All can be calculated. You were getting about 330Wh/mi. You need to get about 242Wh/mi indicated on the trip meter to get 315 miles from 100% (at 315 rated miles) to 0 rated miles, assuming you have a brand new car with no capacity loss.

Your after market lighter wheels are likely marginally hurting your efficiency to the extent they are less aerodynamic than stock (the weight does not matter; it has negligible impact on this sort of drive). However, depending on the tires you have, they could be slightly better than the 20” tires (though they really are not bad). Hard to say. Aero probably worse but rolling resistance might be better.

I thought less wheel surface = more aero?They’re both lighter and smaller. I didn’t expect anything to be less efficient than the chonky uberturbines haha. I was averaging 270Wh/mi, this should’ve given me at least 270 miles. The little peak at the end is me driving in the city.

 

[AlanSubie4Life]

I was averaging 270Wh/mi, this should’ve given me at least 270 miles

Have to look at the trip meter. This is just 30 miles of the trip. Hard to know what your actual average was. If you used 73% of your battery going 169 miles it was 330Wh/mi or so.

And you didn’t get 270Wh/mi at 85mph unless it was substantially downhill or you were following 1-2 seconds behind a big rig going 85mph.

Next time get that data. It’ll all make sense.

 

[Andy Do]

Have to look at the trip meter. This is just 30 miles of the trip. Hard to know what your actual average was. If you used 73% of your battery going 169 miles it was 330Wh/mi or so.

And you didn’t get 270Wh/mi at 85mph unless it was substantially downhill or you were following 1-2 seconds behind a big rig going 85mph.

Next time get that data. It’ll all make sense.

Yeah I should’ve tracked from the beginning. The whole trip was on the same highway at the same speed. Probably some parts were uphill.

 

[ElectricNerd]

Using Autopilot should help a little bit with the efficiency. We've driven that section of I-35 though and you have to be going nearly 85 MPH to not get ran over.

 

[Andy Do]

Using Autopilot should help a little bit with the efficiency. We've driven that section of I-35 though and you have to be going nearly 85 MPH to not get ran over.

Haha yep! I was on Autopilot at 85 and so many people tailgated me

 

[AlanSubie4Life]

Yeah I should’ve tracked from the beginning. The whole trip was on the same highway at the same speed. Probably some parts were uphill.

Under “Trips” or something in the newish UI you can access your trip data since you got in the drivers seat, and since your last charge. That’s the data to look at. I think if you do this again it’ll show closer to 330Wh/mi.

I thought less wheel surface = more aero?

Depends on the surface! The stock wheels at least attempt to be somewhat aero.

Tires are super important too. Just as important as the wheels (though at 85mph the wheels start to be very important).