It’s that time of year again, when we start getting those panicky calls for help:
“What happened to my electric car — I’m sure in the middle of summer my range was much greater than this! My batteries must be dying*already* or my motor, or something!”
So, let’s go over again all the reasons — some controllable — why electric cars “lose range” in the fall and “lose range”:
1) Tire pressure. Tires represent about 5X more of an electric cars “energy budget” than a gas car — because electric cars are alreay about 5X more efficient in the first place. Tires naturally lose 1-2% of their tire pressure every month. And tire pressure varies about 1% for every 10 degrees temperature change. In the spring and summer increases in air temperature tend to offset the normal monthly loss in tire pressure, and you may not have had to put air into your tires. But now, at the end of summer, your tire pressures are probably already about 10% lower than they should be, and as temperature drops off, you lose even more tire pressure. What to do about it? Get a good large dial pressure gauge, and set your tire pressures at least 10% higher than the numbers shown inside the driver’s side door. Some people set their tire pressures even higher than this.
2) Cabin heat. Cabin heaters use a lot of energy. Wear a winter jacket and hat instead, preheat your car while it is still plugged into the car charger, and store it in a garage if possible. Set the cabin heat, if you use it, on the low side. Cabin heat can be taking much more of your energy budget than you might realize.
3) Window defoggers. Window defoggers take a ton of energy. Turn them on for a minute while they defog your windows, and then turn them back off. It is easy to forget and leave them on. Or invest in a good microfiber cloth, and wipe down your windows by hand.
4) Fresh air intake. Most cars default to continuously bringing in outside air — which you keep having to heat up again and again using your precious battery energy budget. Try setting your car to recirculate cabin air. If your windows start to fog up, you may have to turn on outside air intake again for a while.
5) Cabin air filter. If your windows always seem to fog up, then maybe you need a new cabin air filter instead of running the window defogger all the time.
6) Seater heaters, steering wheel heaters. While more efficient than cabin heat, these still take a ton of energy. How hot do you need your hindee? Preheat your car while it is still plugged in, and/or garage it.
7) Car lights. While a smaller part of the budget, contrary to everyone’s expectation, daylight running lights *do not* make cars safer. Leave your lights off during the daylight hours — which are shorter now — so you will be running with your lights on more of the time anyway.
8) Car battery charge reduction with temperature. When car batteries are colder than their ideal temperature, they have less ability to store energy. Your battery effectively, temporarily, gets smaller during the colder months. Garage your car if possible to keep the battery warmer.
9) Car battery ability to give up its charge. Likewise, the car battery is less happy to give its charge to power your car when it is cold. Garage your car if possible to keep the battery warmer.
10) How fast you drive. It may be that you were encountering more road traffic during the summer, meaning you were driving at lower average speeds. At freeway speeds a 10% increase in speed means a 20% increase in wasted energy. A 10% decrease in speed means a 20% decrease in wasted energy — which means a 20% increase in range. Only if you are actually really really stuck in a traffic jam will your cabin heat energy costs exceed the aerodynamic costs of pushing your car through the air. Air resistance pushing back against your forward motion grows as the cube of your car speed. Drive on the slow side if you are worrying about range “zen mode.” Drive 70 mpg “road rage” style only if you don’t care about your range — or the size of your ticket.
11) Traffic jams. If you are really really stuck in a traffic jamb, you may have to consider turning off cabin heat while stuck to preserve your range. Even gassers have to turn off their cars if stuck in a traffic jam “forever.”
12) The thickness of all your car lubricants. Yes, even they don’t have gas engines, electric cars do have 100’s of lubrication points. Over years time, these lubricants all start to break down and become thicker. And in the cold they also, temporarily, become thicker, causing more resistance against forward motion.
13) Your car’s charge setting. Perhaps you are a “hilltop dweller” like myself, who routinely sets your car to only charge to 80% or 90% in order to be able to “regen down the hill?” Perhaps on those cold days you should think ahead and charge your car instead to 100% ?
In my 2011 Nissan Leaf I ran a “controlled test” on a cold day, flat and level on the freeway, exactly 60 mpg, no traffic, “everything turned off” using the advice I offer above, and I found that my energy consumption per mile was remarkably similar to the middle of summer. In short, most of that “winter range loss” is do to things that *you* choose to do, or choose not to do, perhaps without even noticing it. No your battery did not just die, and neither did your motor.
-James Adcock, SEVA Member