Here is my data so far about seasonal changes in battery range for my 2021 Premium Mach-E (RWD, extended range battery). I took delivery in February 2021 in my home city of Windsor, Ontario. For several months I only drove locally due to COVID restrictions at the US-Canada border. When the restrictions were lifted, I began driving longer trips to visit friends in 'the States'. I also began taking consistent data whenever I charged, both at home (Level 2 AC charger) or on the road (usually DC fast chargers). Normally, I charged to 80%.
READER BEWARE: THE DATA AND ANALYSIS PRESENTED HERE IS BASED ON THE INDICATED VALUES OF RANGE AND STATE OF CHARGE. THE RELIABILITY OF THE RESULTS CAN BE NO BETTER THAN THE RELIABILITY OF THE INPUTS.
To get a sense of the battery capacity change over both winter/summer cycles and vehicle lifetime, I devised a variable called 'Full Range Estimate'. FRE can be calculated at any time (while driving or charging) by dividing the Range indicated on the Mach-E instrument display by the 'State of Charge' percentage on the same display. For example, if Range is 150 miles and SOC is 50%, then FRE is 300 miles.
From late August 2021 until late December 2022, I have driven over 22,300 miles and charged 225 times. I recorded Range and SOC at the start and end of each charge, and so have two FRE measurements for each charge. FRE, at each charge start and end, is plotted against calendar date in the first chart attached below.
A seasonal decline in range is evident, with up to 50% FRE lost in winter. Some range loss from battery aging may be indicated by the lower peak FRE in summer 2022 compared to summer 2021. There is also a small but consistent difference with FRE typically higher at the end of a charge compared to the start of a charge. This may an indication of improved (indicated) battery performance due to battery heating during a charge. The higher frequency of charging with time in September 2022 was during a 2,800 mile road trip to the eastern US, and in December 2022 a 7,900 mile road trip from Windsor, Ontario to the west coast of the US.
The second chart attached below plots the same data against distance traveled.
A significant range loss is again evident. The loss is not explained by the distance data alone, but can be explained by independently comparing odometer to calendar date from my charging records. For example, I reached 5,000 miles traveled in mid-November 2021 and 7,500 miles in early April 2022. My road trip in September 2022 ran from 11,600 miles to 14,500 miles. My road trip in December 2022 ran from 16,500 miles to 24,400 miles.
The gradual loss of FRE is also evident in this chart, if one considers separately the summer driving from 10,000 to 15,000 miles and the winter driving from 16,000 to 24,000 miles. The higher FRE at the end of each charge compared to the start is also evident.
For both long trips, I used the 'A Better Route Planner' online app to find chargers along my route. APRP provides a list of chargers and a recommended final charge level at each stop, usually less than 80%. Regardless of those recommendations, I almost always charged to at least 80%.
To more clearly define the temperature effect on FRE, the third chart attached below shows FRE at the start of about 80 charges during the December road trip and a few charges during the September road trip. The overlapping cluster of 5 points with temperatures near 70 F are September data. The linear trend-line and its slope were calculated by the spreadsheet.
The temperature effect can be quantified as the trend-line slope of 1.9 miles FRE increase per each degree Fahrenheit increase. So, if your FRE at 70 F is 300 miles, and you plan to drive in 20 F weather, you can expect to lose about 95 miles FRE ((70F -20F)*1.9 = 95) or about 32% of summer range. That is not an exact value, since there is some scattering in the data.
I plan to continue recording this data and to post occasionally with any interesting results.