Am I looking at this wrong?

[Sprandt23]

So we have hit a good cold snap here in the Midwest, and I'm readily aware that it has significant impact on battery efficiency and degradation. However it has had me keeping a close eye on my usage the last couple weeks, and I want sure if I was looking at this correctly.

I started the day by pre conditioning the battery for more than 45 mins, going from 84 to 94% charge when I started my day. The attached shows my usage from yesterday, slightly more than 100 miles, the majority being commute miles (90ish) with the last being a trip to the movies where it sat outside for a couple hours, losing about 3-4% during that time.

My question is if you do the math, I used 43.7 kW to go 103 miles, not horrible (given it was single digit temps), but that was using roughly 70% of the battery, meaning my max battery capacity would be 62 Kw (43.7 / .70). I know the useable battery actually isn't the full 85kW, I've been reading it is really in the high 70s, but this seems quite a bit lower. Am I looking at something wrong or is there something I'm not considering?

I understand in cold weather my 78ish kW is going to be used faster to go the same distance, but it doesn't seem like I'm getting close to the full capacity.

Thanks in advance for your thoughts, I dont recall it being this noticeable last winter, but maybe I just want paying attention.

 

[AMPd]

I might be mistaken but vampire drain is not included in the energy used number.

 

[Zextraterrestrial]

pretty sure cold temp capacity is less for any(?) battery
probably helps explain a bit of the lower range in cold unless the battery is actually really warm...

 

[Sprandt23]

I might be mistaken but vampire drain is not included in the energy used number.

That makes sense, so 43.7 was what I actually 'used,' but more was definitely 'lost' during the day...surprises me that it might be up to 10-15kW in a given day - I feel like I would only notice a 3-5% drop, even with pre-heating during the day not plugged in. I will take some notes on it over the next few days to get some better data.

The interesting thing was that when I got to 50% charge remaining I switched from percentage view to mileage, and two different days I had 131-133 miles rated - so (theoretically) I would be at 262-266 range at 100% (once battery was warm)...not bad for almost 4 years old I guess.

 

[ewoodrick]

I believe that your starting sentence is where your disconnect is. Cold doesn't impact efficiency and degradation. Cold impacts battery capacity. You're car is going to have close to the same efficiency, just not as much battery as when it is warm.
I had a camera that I took to the top of a ski mountain, it wouldn't even turn on. Tested at the bottom, it worked fine. Next time, took it up to top inside my jacket, it worked fine. No charging, just temperature changes.
When warm, it had 100% capacity, when cold (-30f) it had 0%. Warmed it back up and back to 100%.

Just think of the energy in the battery as being frozen

 

[Sprandt23]

I believe that your starting sentence is where your disconnect is. Cold doesn't impact efficiency and degradation. Cold impacts battery capacity. You're car is going to have close to the same efficiency, just not as much battery as when it is warm.
I had a camera that I took to the top of a ski mountain, it wouldn't even turn on. Tested at the bottom, it worked fine. Next time, took it up to top inside my jacket, it worked fine. No charging, just temperature changes.
When warm, it had 100% capacity, when cold (-30f) it had 0%. Warmed it back up and back to 100%.

Just think of the energy in the battery as being frozen

Hmm...I was not thinking of it that way. I was definitely of the impression that it impacted the battery efficiency, given that my lifetime usage is slightly over 300 Wh/mi - and almost all day yesterday when we were in single digit temps I was barely able to get below 500 Wh/mi. Does that not reflect battery efficiency changing due to colder temps? No battery engineer or expert here by any means....

 

[JoeMartin]

I have a 2014 P85 and my battery maxes at 73.6 Kwh.
Unfortunately I bought mine at a little over 50k miles, so I can't say what it was when it was new.

 

[AMPd]

I believe that your starting sentence is where your disconnect is. Cold doesn't impact efficiency and degradation. Cold impacts battery capacity. You're car is going to have close to the same efficiency, just not as much battery as when it is warm.
I had a camera that I took to the top of a ski mountain, it wouldn't even turn on. Tested at the bottom, it worked fine. Next time, took it up to top inside my jacket, it worked fine. No charging, just temperature changes.
When warm, it had 100% capacity, when cold (-30f) it had 0%. Warmed it back up and back to 100%.

Just think of the energy in the battery as being frozen

That’s simply not true. The cold definitely impacts how efficient the car is

 

[tga]

That’s simply not true. The cold definitely impacts how efficient the car is

Yes, cold air is denser and results in more wind resistance. Plus the heater uses lots of power, especially when bringing the cabin up to temp. Last winter I was on a road trip with 15 mph headwinds in -3F temps. The car used more than 500Wh/mile on the highway.

On short trips around town (where the car has to heat up each time), I've seen 700-800 Wh/mi.