Monday 2nd April 2012

Does temperature affect range? The ActiveE features a system to manage the temperature of the battery in a way the MINI E never did. Where the ActiveE has a water filled, heated and cooled jacket around the batteries to keep them all snug at the right temperature, the MINI E just sucked air from the inside of the car through vents to the batteries. This extra effort in the ActiveE is all to improve the consistency of the available range. The MINI E would swing from 120 miles range down to as little as 86 miles on a frosty morning.

For the past month or so I’ve been diligently recording the temperature and the available range in both regular and Eco mode to see if, despite our mild winter, there is still an impact on range. Guess what? There is…

This is a graph of ‘regular mode’ and ‘Eco mode’ predicted miles against temperature.

As you can see, as the temperature goes up and down, so does the range – it’s almost directly connected. You can also see from the trend lines that summer is on it’s way! With it, some more miles in the ‘pot’.

As time passes, the difference between regular mode and Eco mode is becoming less pronounced.  I drive in Eco mode all the time whereas Michael drives in regular mode, this shows that Michael’s driving is getting better.  Not sure you would see the same if he did this with the Tesla!

Update April 4th

Here’s another way to look at the data, this time using a scatter plot as suggested by John Briggs:

You can also download the data here.


SHOWHIDE Comments (8)
  1. Interesting. Would be nice to see it in an X-Y scatter plot rather than against time.

    1. Pamela tracked Date, miles range, miles range ECO and temperature. Not sure how to make an X-Y scatter plot – got any guidance?

      1. Perhaps plot range vs. temperature, and see a linear correlation; since the date is not really a relevant factor

  2. The correlation looks so close as I’d basically guess that the BMW is measuring battery and air temp and using those as the single biggest modifier to the battery charge level. There’s probably something about how the car was driven the previous day or two thrown in.

  3. Oh, excellent. Sorry I didn’t check back in on the discussion until now.

    Despite some significant (and to be expected) scatter in the data, the trendlines clearly shown the story.

    This data makes it clear that for about a 20C drop in temperature there is a 10 to 15 mile drop in range.

    We should keep in mind that ICE and hybrids have a similar problem. My Prius drops from 55 mpg in the summer to 45 mpg in the winter. Part of this is slightly higher air density in the winter, part is poor ICE efficiency in the cold. We should just know that this isn’t necessarily just a battery or heater issue.