State of Charge plummeting in cold weather

[jsmay311]

The specific heat of the pack is in the range of 850 J/Kg*K. From Bjorn's videos, I think active pack heating is in the range of 6 kW. A - 80 kWh pack weights about 800 Kg

So you tell me: how many degrees C will the pack heat up per minute with directed pack heating ?
My arithmetic says 0.5 C/min if 6 kW of heat is directed to the pack. If cabin heating is splitting the heat, then the pack heats up 0.25 C/min

Idk how reliable the weight numbers floating around online are, but I’ve seen it posted that the Model 3 pack is 1060 lbs (480kg) and the Model Y pack is 1700 lbs (770kg). I find it surprising that there’s such a big difference since they have similar kWh capacities, so idk what to believe.

But your math is right, albeit simplified, if you use your assumed battery pack weight and specific heat. But, in addition to heat loss to the environment, you also need consider that the drive units and the coolant itself have to heat up before they can deliver heat to the battery, so that’s more thermal mass that will require additional energy not going to the battery.

Here’s one real-world example where my 2018 Model 3 LR-RWD used ~8% of its battery capacity over the course of 97 minutes while parked just to heat the battery before a scheduled departure. Unfortunately at that time I had no way to see actual battery temps (I relied on TeslaFi to see power and energy usage and SOC drop) so idk how many degrees the battery heated up. And a RWD sans heat pump would perform differently than an AWD with heat pump.

 

[KenC]

It says "going downhill saved 1.2%".

Actually no. Uphill cost 1.4% and downhill cost 1.2%, that's just the ups and downs of normal driving. I went to the gym, and it's actually uphill in the last section.

 

[sgmstr]

I'm just entering my 4th winter with my 2020 M3LR. Yesterday I parked the car at 12:30PM. It had 154 miles of range. The temperature was just above freezing. Overnight the temperature got down to about 26 degrees(F). Now, after being parked for about 22 hours the car is down to 140 miles of range. I don't remember the cold having this much of an impact on my cars range in previous winters and am wondering if something else could be contributing to this sharp drop in range. Any thoughts???

Did the loss of range shown anywhere on the screen in addition to SOC level? I started parking my car outside (usually lowest is above freezing) and have been experiencing loss of about 2% a day as opposed to closed to zero when parked inside (usually 55F). That loss is shown as used on "Vehicle Standby". I didn't change any settings when I started parking outside (other than just now turning off wifi completely thinking that may be the cause). This leads me to think it is using energy to keep up the battery warm when cold at night, but I thought the battery doesn't precondition/heat/keep warm when car is NOT in use. Weird.

 

[Shelburne]

The battery only preconditions when you schedule it to via the app

 

[Maki22]

The battery only preconditions when you schedule it to via the app

It also preconditions if you turn on the HVAC through the app.

 

[MikeRTX]

It also preconditions if you turn on the HVAC through the app.

Isn't that CABIN preconditioning, as opposed to battery preconditioning?

 

[surfrasch]

by the way, I think all these battery range indicators changed with 2023.44.30.5.1. This is when my fully charged range dropped immediately, and also my car is exhibiting the same range drop in cold behavior. I think it's all related.....though I'm a little surprised....my garage is holding in the mid 40's F and my battery range is still dropping. I would think it would have to be much colder, but apparently not. Mid 40's is summer in a NH winter!

 

[Maki22]

Isn't that CABIN preconditioning, as opposed to battery preconditioning?

It does both if the battery is cold, you will notice a heating icon next to the battery indicator in the app when it preconditions the battery.

 

[sgmstr]

The battery only preconditions when you schedule it to via the app

You're right. I deleted/forgot wifi for the home and it stopped draining battery. Turns out temperature was not the issued. I remember watching YouTube video of a a guy testing his MX in 0F temperature and didn't use any energy on "vehicle standby".