The forecast of how far the car can go before it runs out of electricity is a question many owners get frustrated by. It's rarely a consideration on a ICE as the available miles can be easily and quickly replaced at a fuel station, however when you are in an electric car with a displayed range below 100 miles or 150 km, if you are a long way from home then the thought of charging soon starts to be a real consideration.
Firstly, there is no 100% accurate way of knowing future range because its predicated on how the car is driven and the environment in which its driven.
Just like an ICE car, an EV will have a formal quoted range/efficiency. This will be based on EPA, NEDC or WLTP depending where you are in the world and even when your car was made and they all differ to a greater or lesser extent. ICE are the same, few cars get the published MPG or l/100km figures.
One element often causing confusion is whether the range reflects the driving style or efficiency of the owner. It does not except on the Energy use screen, it is based on a fixed amount, the definitions of which are explained below.
The Rated range is based on the testing standards in country the car is sold in. The figure will vary by model as the efficiency varies, the Performance MX on 22" wheels being the worst with a Model 3 on 18" Aero wheels being the best, the EPA and WLTP being the most realistic with the NEDC being the most optimistic and unrealistic. This is a fixed consumption rate and the miles displayed is the battery management system (BMS) estimate of available kwh divided by the consumption rate.
Increasingly it seems the cars now only show the EPA range irrespective of which country they are in.
This is virtually identical to the Rated range in concept, except the figure used by Tesla is a more realistic guess of the efficiency for the car and universally worse than the Rated range. The benefit is that the range on the dash is closer to a realistic range but it is still inaccurate being more realistic if the car is driven at around 65mph or 110km/h in reasonably good weather.
Rated Range is only an option on older cars in countries where the NEDC ratings were used as a counter to the wildly optimistic figure from that testing system. Cars classed against the WLTP system which replaced the NEDC don't have a Typical range option.
To change between Typical and Rated, you select which you prefer in menu, although increasingly cars now only show the rated range.
This one is used less today and was a version of the range when driven in Ideal conditions, thought to be around 50mph. As battery sizes have increased in general, the need to know the maximum you could eek out of a car has become less important.
The only place you can see a range based on recent driving behaviour is to display the energy screen and look for the projected range figure. This uses the average energy consumption over the distance range selected and uses this and the BMS reported available kwh to work out a range. There is also an option to show this on instantaneous consumption but this is of little benefit.
In addition to the range figures, the car can show the economy of the car, this is typically the economy on the last journey, spanning short stops and the economy since last charged. It's worth knowing what your car used for Typical consumption as a mental reference against which you can compare, for instance a Model S is around 300 wh/m unless it's a performance which is nearer 330 wh/m. You can then mentally gauge whether you're exceeding this considerably or not.
One of the most hotly debated topics is whether you should show a range at all on the dash or just show a percentage. The argument is that as the range is always wrong, don't display it, The counter argument is the percentage doesn't really tell you anything either, and at least a rough mileage is better than no mileage. Miles of range is a direct proxy for the number of kwh in the battery (typically about 3 miles is 1kwh although the exact ratio varies by model) whereas the % is just the fraction of the battery pack that's available and any loss of battery capacity reduces what a % stands for.
We display range, we let the battery icon give us an indication of the fraction of how full, but there is no right or wrong.
We've mentioned previously that the range displayed may now be that under the WPA rating system while cars outside the America often use the WLTP system and as a consequence the 'rated range' is not the number owners were expecting, however in this situation the difference is not battery degradation.
If you are concerned or want to know the degradation we have created a guide to calculating your battery degradation which helps you calculate the degradation with just a few simple pieces of information.
One aspect of Tesla ownership that surprises some people is the car uses electricity even when not being driven. This is called Vampire drain. This can range from a few miles per day to quite significant amounts of energy that could deplete the battery within a week.
To reduce vampire the following steps are recommended
A combination of the above will minimise the vampire drain in the car and reduce the amount of battery loss over night or whenever you leave the car.