I'm missing 14% of my battery capacity...any ideas?

[BoilerG]

I decided to run down my battery to <20% on my April build S75. I can't figure out why, but I'm missing 14% of my battery capacity and was wondering if anyone here had any insight. Here are my numbers:

Capacity: 75kWh (verified by sticker under car)

Charged to 90%: 10% capacity
Usage Since Last Charge: 58% capacity (43.2kWh)
Remaining on battery: 18%

Total: 86%

Where is the remaining 14%?!

 

[oneday]

A/C, heater, pre conditioning, and vampire drain is my first thoughts.

 

[eye.surgeon]

That's not how it works. You don't have access to the full capacity of the battery.

 

[chillaban]

The trip meter does not count any of the power consumed when you're stationary (e.g. cabin overheat protection, vampire losses, AC revving up when you just unlocked your car, etc etc etc.)

 

[BoilerG]

A/C, heater, pre conditioning, and vampire drain is my first thoughts.

Pre conditioning is off.

A/C is factored into my Wh/mi (which is why it’s so high).

This was over about 60hrs so that would be faster vampire drain than what I’ve read from others.

If I can’t access my full battery, the car shouldn’t be rated for 249 miles.

75kWh/(300 Wh/mi) = 250. Car is rated for 249 so pretty darn close to all capacity is used for rating the range.

 

[markwj]

Here's an example for an 85kWh battery. Short answer is the percentages shown don't include the top and bottom reserves.

 

[BoilerG]

The trip meter does not count any of the power consumed when you're stationary (e.g. cabin overheat protection, vampire losses, AC revving up when you just unlocked your car, etc etc etc.)

This makes some sense but 14% for cabin cooling is a lot considering the car was almost exclusively parked in the shade. Given that the AC draws about 10A at 240V when plugged in (at max power) that’s about 2.4kW for every hour it’s run. I know the cabin didn’t precool for 4.4hrs since it never reached 105 inside. I watched from my phone

 

[BoilerG]

Here's an example for an 85kWh battery. Short answer is the percentages shown don't include the top and bottom reserves.

View attachment 248868

Good chart. If we can’t access a portion then they shouldn’t show it as part of the range, right? If ~5% is held for brick protection than shouldn’t it be rated for 238 miles max? On a trip charge I get 247 miles shown so my battery degradation is theoretically low too.

 

[GasKilla]

Did you look between the seat cushions?

 

[BoilerG]

Did you look between the seat cushions?

I think I heard it under the floor.

 

[eye.surgeon]

This makes some sense but 14% for cabin cooling is a lot considering the car was almost exclusively parked in the shade. Given that the AC draws about 10A at 240V when plugged in (at max power) that’s about 2.4kW for every hour it’s run. I know the cabin didn’t precool for 4.4hrs since it never reached 105 inside. I watched from my phone

Your question has been answered twice already and it has nothing to do with vampire loss or cabin cooling. You don't have access to the full capacity of the battery.

 

[BoilerG]

Your question has been answered twice already and it has nothing to do with vampire loss or cabin cooling. You don't have access to the full capacity of the battery.

Then why does Tesla rate the mileage as if we do? My car should not be rated at 249miles of range if we can’t access all of it. That’s a false claim then.

 

[stan23]

Then why does Tesla rate the mileage as if we do? My car should not be rated at 249miles of range if we can’t access all of it. That’s a false claim then.

because if you drive in a perfectly flat surface with no wind and going 45 mph, technically it's possible to get 249 miles of range.

 

[eye.surgeon]

Then why does Tesla rate the mileage as if we do? My car should not be rated at 249miles of range if we can’t access all of it. That’s a false claim then.

Rated range correlates only to the usable capacity of the battery.

 

[stopcrazypp]

Then why does Tesla rate the mileage as if we do? My car should not be rated at 249miles of range if we can’t access all of it. That’s a false claim then.

The EPA range is based only on usable range. The EPA test does not care at all what the actual full capacity of the battery pack is. When the car is unable to keep up the cycle, the test stops (does not matter what the dash says, even if it says it reached zero many miles ago).

 

[Max*]

Here's an example for an 85kWh battery. Short answer is the percentages shown don't include the top and bottom reserves.

View attachment 248868

That's a very outdated image. There is no zero mile reserve. People keep posting this, someone will run out of juice and say "hey, I read there's a zero mile buffer at the bottom of the pack".

 

[Max*]

Then why does Tesla rate the mileage as if we do? My car should not be rated at 249miles of range if we can’t access all of it. That’s a false claim then.

Take a road trip, you'll get close to 249 miles if you drive 55-65mph in 70F weather.

Doing the trip over 60 hours is a horrible test for many reasons
1. Vampire drain. I think my car loses about 3% per 24 hour period. That wont be reflected in the "kwh" used or the available miles for you to use.
Extrapolate that out to 60 hours, and you'd lose about 7.5% or 18miles. Just from being parked.

2. Doing a lot of short trips is much harder for "range" than 1 long trip. So over those 60 hours, how many trips did you take? Each trip needs to warm the battery (though in Dallas, your lows look to be in the 70s, it might not be warming the battery). Cabin cooling/warming I believe is included in the total kwh number, though I can't remember.

3. The biggest issue is with that kwh calculation number. It's not valid for what you're testing. Do a road trip. Seriously. You'll see that kwh number show that you got a lot more kwh out of the car on a single charge (even though in reality, the true kwh out of the car would be the same). Since you're taking out all the loses over time that the kwh number is not calculating, you'd get a lot more range out of it too.

 

[hill]

That's not how it works. You don't have access to the full capacity of the battery.

also as previously discussed, 75kWh term is just advertise rounding. A new 60kWh pack has 62kWh's & a 75 only has 72kWh's. it wouldn't sound as cool to advertising a 72kWh pack. think about it, if you upgrade from a 60 to 75, it just doesn't feel like you gat as much bang for the buck if you only get 10kWh's verses 15kWh's on an upgrade.
.

 

[Max*]

also as previously discussed, 75kWh term is just advertise rounding. A new 60kWh pack has 62kWh's & a 75 only has 72kWh's. it wouldn't sound as cool to advertising a 72kWh pack. think about it, if you upgrade from a 60 to 75, it just doesn't feel like you gat as much bang for the buck if you only get 10kWh's verses 15kWh's on an upgrade.
.

So updating his math using 72kwhs. And there's an anti-bricking buffer of what, 4kwh? So the total usable battery capacity is 68kwh.

Charged to 90%: 10% capacity
Usage Since Last Charge: 64% capacity (43.2kWh)
Remaining on battery: 18%

Total: 92%

So he "lost" 8% from vampire drain over 60 hours, seems reasonable based on my experience.

 

[Zaphod]

Do you have any of the power savings on? Also, if you are constantly checking it with your phone, you are waking it up (if it was asleep) all the time and further compounding the power drain.