A friend asked, "What is the range [of your Tesla Model S]? Do you have the smaller battery or bigger one? Have you taken it on road trips where there is mountains and how does that affect the batteries?" Range is a very common question among electric vehicle potential buyers, and the short answer is "it depends". I have the 90kwh battery with a rated range of 265 miles, which is one of the larger sizes available. The largest battery size available is currently 100kwh, and the minimum from a new vehicle is 75kwh. Keep in mind that I have the P (Performance) model, which tends to be less efficient than the non-P. I get ~265 miles (especially with highway driving) during most of spring/summer/fall and a small portion of winter when it's around 50+ degrees; in fact, I've gotten over 300 miles range out of my car--not that I actually drive it to 0 miles remaining. What I mean is my efficiency was good enough to get that much range. For example: I just took a road trip to St. Mary's County (75 miles each way) and averaged under 250 Wh/mile. Given that my car has a 90kwh battery, if I charged it to 100%, then here is the math to determine my actual range at 250 Wh/mile: 250Wh/mile * 4 = 1kwh. My car has 90kwh, so multiply 4*90 = 360 miles of range. Since I believe my actual efficiency was 239 Wh/mile, I could do 360 miles with a little to spare. The best I've seen was on a road trip to Shenandoah Valley (I did the 100 mile Skyline Drive) where I saw 190Wh/mile and routinely in the 200's for almost the entirety of the drive. As far as impact on range due to mountains/hills, what one needs to consider is Net Elevation Gain. As long as you go back down a mountain, you'll regain most of the energy spent to get up it. I've heard online that the regenerative braking system is better than 80% efficient; in other words, if the car speeds up to 40mph then allows the regenerative brakes to take it to a complete stop, it will regain ~80% of the energy spent. I'm sure that some of that ~20% energy is lost to friction from tire rolling resistance, electric heat, running the vehicle electronics, etc. The smaller the wheel and less heavy it is, the less rotational weight the car must overcome. You'll see an improvement in range when running 19" wheels on the Model S vs 21" wheels on the Model S. My car started with 21" wheels, which I swapped out for 19" wheels. I saw an improvement from efficiency around 400-450Wh/mile on average to into the 300's. In addition to the wheels, the tire tread compound has a large impact on range due to rolling resistance. A less grippy tire will be more efficient but suffer worse cornering capability. I'm pretty happy with my 19" wheels with all-season Michelin Sport tires as a compromise somewhere in the middle of grip/rolling resistance. It's also a pain to swap out wheels + tires twice a year, so even though the 21" wheels are beautiful, I plan on selling mine soon and keeping the 19" wheels all year. The Model S gets the best efficiency on the highway; in the city, I'll see ~350-400 Wh/mile, which is a little worse than the rated 265 miles ideal range. How do I know that? Read below... So, what efficiency must be driven to get 265 rated miles out of a 90kwh battery? Another math equation: 90kWh/265 miles = .339 kwh/mile. Convert to Wh/mile as follows: .339kwh/mile * 1000 = 339Wh/mile. So, as long as you drive at 339Wh/mile or better efficiency for the entirety of a drive, you will see at least 265 miles rated range. During the winter is when you'll notice a very significant drop in range due primarily to the following factors: 1. The heater uses up to 6kw of energy. Run that for an hour at full blast, and that's 6kwh of a 90kwh battery used up just to heat the cabin. 2. The battery's energy density decreases when it is cold, like during the winter--especially in sub-50 degree weather. How to compensate for these factors? Pre-heat the cabin using the phone app before driving. This will not only make the car comfy from the start, but it will save your range AND preheat the battery to a certain extent. Instead of using the cabin heater, use the seat heaters (standard on all models) and steering wheel heater (winter package). It also helps to dress warm with gloves and hat! Keep in mind that for long distance driving, you only need enough range to get to the next supercharger. The superchargers tend to be spread out at a max of ~125 miles between chargers. Since you're unlikely to pull into a supercharger with 0 miles remaining, let's say you need to charge enough to get 150 miles to easily reach the next supercharger. The superchargers currently charge at up to 135kw/hour, but the speed at a supercharger depends on a few factors: 1. Usually a supercharger stall has up to the max charge rate, but that charge rate is shared between two outlets from the given stall. 2. The car significantly limits the charge rate from the supercharger once the battery has reached ~80% capacity. If I'm getting 135kwh/hour from the supercharger, then it's possible to charge from 0-72kwh (80%) of my car's 90kwh battery in 72kwh/135kwh = 0.533 hours, or a little over 30 minutes. So generally speaking, ~20-30 minutes at a supercharger is enough time to get to the next one with some range to spare.