The purpose of this post is to report some practical experience with a Model S 70D in winter. The focus is on energy consumption and real range, not on other aspects of performance. When I ordered my 70D last summer (July 2015), the model had only been available for a few months, and no one had experience with one in winter. I had been following Tesla for more than a year, had test driven cars two or three times, and had read a great deal, especially in the TMC and Tesla Motors forums. In addition, I had watched quite a few videos, mainly those created by Bjorn Nyland in Norway. Most of the videos reported experience with the 85 kWh battery models. My judgment from what I had read and heard was that the 70D would be a practical car for me. I was newly retired, and thus have no regular commute. I really did not know how much driving I would do but I did not expect to be driving further than the 70D’s range very often. In terms of winter battery range, I think I was influenced in my expectations by Bjorn’s videos. I can recall Bjorn saying that the cold did not have very much effect on his car’s range, and that rain and snow had more effect. What I now realize I did not appreciate was that Bjorn’s videos are mostly about very long trips, not the sort of local travel with multiple short trips that is most of what I do. In retrospect, I also think I was wearing rose-colored glasses to some degree. After all, I was smitten with the Tesla and was going to get one regardless! Now that we are a few weeks into winter, I thought I would offer some statistics on my experience with the 70D in winter. I have seen plenty of reports of individual trips in winter by various models, but not of average consumption over a period of time. And just to be clear – I am not suggesting that the 70D would perform significantly differently from the other battery configurations. It is just that I have a 70D, and it is the first year for this model. Weather -- Here in the Boston area, we had a very mild winter until just recently. December and January both ran well above normal averages. In January there were 4 days with high temperatures in the 50s, and many in the 40s. Daily low temperatures were mostly in the 20s, with only 5 days with a daily low below 20. February has been colder so far, but still somewhat warmer than usual, until this past weekend when we had a severe cold snap. I limited my statistics to January and February (through February 15), because December was so warm it would not be representative. In the 6 weeks of January and early February, I drove 1,045 miles. I tracked the kWh added each time I charged, and calculated the average Wh/mi. (In the interests of full disclosure, there were 3 data points for which I failed to record the kWh added by a charge, so I inferred the energy added from the reported change in rated range, using the figure of 292 Wh/mi, which corresponds to the rated range of 240 miles for the 70 kWh battery.) On average, my car used 549.7 Wh/mi. This seems quite high, and is equivalent to saying that the effective range I achieved was 127.3 miles, or 53.1% of the rated range of 240 miles. The consumption rate (Wh/mi) or effective range varied by date, of course, because of both weather variations and differences in my trips. The highest I saw was 725 Wh/mile for the frigid cold in this past weekend. But the cold weather was not the only factor at play here. The other factor, and maybe the most important factor, is that most of my travel is short trips, 5 miles or less, with occasional longer trips. So my energy efficiency is likely much lower than someone who commutes a long distance, for example. Every time I get into my car, it uses energy to heat the cabin, and then that energy is lost while the car sits idle between trips. Thus I probably use a lot more energy than many other owners because of how I use the car. So my statistics may well not be representative of others’ experience. One other comment I will offer, especially for people considering a purchase, relates to the effective battery capacity. Tesla refers to the 70D as having a 70 kWh battery, but then recommends that you charge only to 80 or 90% unless you are going on a long trip. In addition, the battery starts to encounter restrictions in performance when its charge level drops to about 20% (or even before). So the consensus among owners seems to be to maintain the battery between 20 and 80% if you can. This means that the effective useable capacity is 60% of 70 kWh, or 42 kWh. When you combine that practice with the higher consumption in winter, you can find yourself quite restricted. E.g., using my average value of 549.7 Wh/mi and 42 kWh, that implies a driving range of only 76.4 miles. And in fact, my average distance traveled between charges was 70 miles, with 111 miles being the longest I drove between charges in this period. (That 111 mile interval included a pair of trips of 20+ miles, so the energy use per mile was reduced.) Obviously, you can obtain much higher practical ranges by charging the battery to 90% or more when you need to, and driving until the battery charge is less than 10% if you are certain of where you can charge. And your range will be higher for longer trips – again, my driving pattern may be on the extreme end of inefficient, short trips, and thus unrepresentative. My own conclusions from this exercise are: 1. Short trips are a huge factor in energy consumption in winter, because of the energy spent to heat the cabin, for each trip no matter how short. 2. The battery limitations at less than 20% charge (on regenerative braking and preheating), combined with the limitations of cold weather (restricted battery reserve and reduced charging rate) are strong incentives to avoid discharging the battery that much if you can avoid it. 3. By the same token, if the cold is severe, consider charging to 90% or more to ensure you have the range you need. 4. The advice to “buy the largest battery you can afford” is even more important for people living or travelling in cold climates. What I would like to do is to take some longer trips on a cold day and compare the energy use of the 70D with the data reported by other people for models with the 85 Kwh battery. I will try to do that if time and weather permits and report the results. The intent of this post is to inform. This is not a criticism of the car – I love my Model S! But I think it is important for people to understand the facts of cold weather effects on range. Side note: Each time I charge, I record the data from the Trips screen for “Since last charge.” I found in doing this analysis that that data is sometimes incorrect. I have seen other posts that noted issues with the Trips screen since the version 7.0 software release so I did not use those data in my analysis.