Tesla Range & Seasonality

Originally published on the Tesla Motors Club forum.
By FlasherZ

I posted some rough data in the 90% thread and the 90D thread, but felt it might be appropriate to pull another thread here when discussing range and degradation.

It’s starting to get colder here in the midwest, and my displayed range after charge (at 90% and 100%) has been dropping again, as it has for the past few years when the colder weather rolls in. I’ve also noticed it picks back up in the spring.

So I put my database of information from my car to good use (it dates back to October ’13, data corruption destroyed the DB prior to that date) and graphed my range for both 90% and 100% charge levels.

Here are the two graphs. First, 90% (selection criteria – all points, API battery_level = 90):

Tesla range

Next, 100% (selection criteria – all points, API battery_level = 100 (that’s right, I am not afraid to range charge!):

Tesla charge

As I noted in the other threads, I have not done any correlation with temperature, distance from range charge / rebalance, or software updates. I did go back and look at the anomaly that occurred on late Feb, 2014, when the graph does a correction upward. After thinking about it – this was the date that my rev A battery pack was replaced with the refurbished rev D pack following the contactor failure.

Note that this is not the same thing as the snowflake that “reserves” some range in ultra-cold temps – this is the car’s interpretation of the range of the battery.

Conclusions to reach here: range display is seasonal and as you enter winter months, you may not be experiencing the degradation that you think is appearing… it’s likely that it comes back in spring.

Addendum (in Response to a Question/Request)

Here’s what a moving-average overlay looks like. Blue is 2/25/2014-2/24/2014, Green is 2/25/2015 onward:

tesla range temps

Another view… here is the monthly average range at 90% charge (mean of all values within a month beginning with the date on the X axis). EDIT: I completely forgot I had an easy source of comparison with regard to temperature. I have the car’s “outside_temp” data. Here’s an overlay of the average outside temperature (as registered by the car, deg C, unheated garage) with the average range:

Tesla Range Temperature

One more — the full data series for range vs. temp, rather than average. There are roughly 55,000 temp samples and 11,000 90% range samples over the time period:

range vs temp
(You can also see where the holes in my data are due to the sampling getting “stuck”.)

In a quest to find tighter correlation, I did some more work. This time, I pulled temperature samples only within 30 seconds of the 100% SOC range samples I had pulled.

range vs temp 30sec

The correlation is now tight, with only two explainable areas of disconnect: 3/2014, just after the new pack had been installed; and 8/2015, just after my car’s energy data had been reset due to the accident repairs from colliding with a deer.

Reprinted with permission.

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