Battery Drain, Low Range, Range Math

[drg_mx]

car- 21-month old 2017 MX, 90D, 19500 miles, OAT 70-75, ac setting 73.

from day 1, i have felt that i am not getting enough range, at times barely 130 miles when the energy meter goes red (<40 miles remaining). since most of my driving is local, this has not been an issue but the numbers have been bugging me.

so i have been watching numbers like miles, range, watt-hr/mi etc. see the 2 attached shots, for this test, the starting point was 100% charge, range prediction was 254mi.

from interpretation of the numbers, the math does not add up. it says...

Q1...driven= 81.3, remaining 123. that is a total of 204.3... happened to the missing 50 miles?

Q2. watt-hr/mi numbers are 375 and 359 (from the energy curve) and energy consumed = 30.3 KWH, so remaining battery is 59700 watt-hr (90-30.3). so the remaining range should be 158mi ( 59700/375=158). missing 35miles (158-123) .....what happened to the 35mi ?

Q3 . is power-usage by a/c or heater not included in the displayed prediction? note the weather during this test been CLOUDY and very moderate so a/c use should be little.

any thoughts or correction to my math/interpretation?

thanks

 

[srachamallu]

are these drive stats from same day? try using teslafi and see what is causing the drain. @100% 254mi shows that no battery degradation happened and something else is causing the drain. On my M3D if I leave sentry mode depending on the traffic in parking lot it drain any where from 8 to 10mi in 8 hours, also cabin overheat protection also causes drain as it wont let car to go into deep sleep mode.

 

[Saghost]

Tesla uses rated miles, unlike most of the rest. That means the range of 254 miles is 254 miles if you drive like the EPA test.

Drive faster, accelerate harder, you'll get fewer miles.

So the missing miles in the first question are the mostly the difference between how you drove and how they tested. Getting 375 Wh/mile is further indication of this - I think rated range for that car is at about 320 Wh/mile.

For your second question, you're assuming that you are using 100% of the physical capacity of a battery pack that has exactly 90 kWh of storage.

Neither of these is true. Tesla keeps about five percent at the bottom as a bricking reserve - otherwise when you ran the battery to zero it would have to be replaced.

When new, I think the nominal capacity of the 90 kWh cars was around 86 kWh, and you've probably lost around five percent to degradation from there.

It's a little unclear how HVAC is factored in to Tesla efficiency numbers. I'm not quite certain, but I believe it includes HVAC while the car is in Drive, but not otherwise. Certainly HVAC turned on by the App before you get in the car is not included.

 

[animorph]

The number of miles/km by the battery icon is not a "range prediction". It's a simple measure of the energy available in the battery in terms of official EPA consumption. If you drive like the EPA it might be accurate. Just like any car, it's range depends on how you drive, speed, elevation changes, weather conditions, temperature, load, the roads you are using, and more. The car has no idea what you're going to do, unless you enter a destination in the nav. In that case the nav will give you an estimate of the charge remaining at the destination. That is usually a pretty good estimate, but still can still be off if you decide to floor it all the time or conditions are different than the last 10's of miles.

The "90" batteries were optimistically named. There is a buffer. There are internal losses that are not measured by the car. There may be energy usage not included in the trip info. There are vampire losses. Lithium batteries can output more energy per charge at slower discharge rates than higher rates.

You can probably find 100 threads on this subject on TMC. It seems to be especially popular recently. Here's my favorite one:
Car’s energy consumption (lack of) accuracy

I haven't seen anyone completely reconcile the trip consumption info to battery capacity and charge energy. Pretty much like trying to do the same with an ICE car. A full tank of gas in my Porsche was always a gallon or two short of claimed capacity because a gallon or so was used to fill the fuel system and was basically unusable. And I never got anywhere near EPA mileage.

 

[drg_mx]

are these drive stats from same day? try using teslafi and see what is causing the drain.

thanks SRACHAMALLU ...these are over 2 days...but following your suggestion, i will try doing a test in one run of 60 - 70 miles and retest.

So the missing miles in the first question are the mostly the difference between how you drove and how they tested. Getting 375 Wh/mile is further indication of this - I think rated range for that car is at about 320 Wh/mile.

For your second question, you're assuming that you are using 100% of the physical capacity of a battery pack that has exactly 90 kWh of storage.

thanks SRAGHOST
ok and ok...so even using 85 KWH as total energy available, i should get "remaining=146 miles" ((85-30.3)/0.373) as i am using MY ACTUAL consumption. (not using the rated). isn't the 373wh/mi calculated by the car based on my ACTUAL driving?

the nutshell is-- my usage (based on my driving) is about 373wh/mi...i will stretch it to 400. then using the reserve you mentioned (say 5KWH) , i should be getting 212 miles (85/.4) from a full charge....in reality, the best i ever got (from full charge) was about 177 miles (estimating the last few miles) as the meter showed remaining down to 20 miles.

NOTE- before this MX, i had model S, and did not have this kind of discrepancy in range math.

 

[drg_mx]

I haven't seen anyone completely reconcile the trip consumption

you can add me to the list for MX...however, as mentioned, i had very little discrepancy with MS.

the question is why is it more popular now? is it because people like me are finally taking note or tesla has changed the way they calculate/predict?

appreciate the link animorph..will do some more digging