At about 7:30AM, ambient of 21F/-6C, with my bike cold-soaked in a unheated garage to ~35F/2C, I rode 21.8 miles (~35 minutes). I plugged in at work, and the kill-o-watt registered 3.2 kWH to charge to 100%. By 4:00PM, with the ambient up to 62F/16C and some sunshine on the bike, I rode the exact same route, and plugged in at home. This time, only 2.4 kWH. No wind today, no significant change in elevation, just different temperatures.
In the cold it took 33% more power to go the same distance! I knew there was an effect, but I never really measured it, pretty dramatic. Where does the extra power go?
"Cold temperature increases the internal resistance and diminishes the capacity. Batteries that would provide 100 percent capacity at 27°C (80°F) will typically deliver only 50 percent at –18°C (0°F)."
http://batteryuniversity.com/learn/article/discharging_at_high_and_low_temperaturesSo I guess this means that the extra 800 Wh that was used in the cold went into heat dissipation in the battery through the "increased internal resistance" mechanism? I find this a little bit hard to imagine as that's a lot of heat - like a hair dryer running for 40 minutes. I would think the battery pack would have been pretty toasty at the end of the ride, even with the ambient of 21F/-6C.
Does anyone have any insight into this? I'm curious to learn more.