- Capacity of the battery
- Cold weather
- Driving mode, style and speed
- The efficiency of the car’s motor and control system
*BMW doesn’t use kWh to indicate the battery capacity. Instead they use Ah (amp/hours)! BMW i3 120Ah battery = approx 42 kWh.
2. Cold Weather
Cold temperatures have a negative effect on battery performance. ALL batteries perform poorly in cold weather, regardless of whether they are lithium or lead-acid. In winter temperatures, say up to around 7 deg C or 45 F, range will typically reduce by around 25% but below freezing this can increase further. In a gas/petrol car you get free cabin heat via the waste heat from the engine, but in an EV that heat needs to come from the battery which is a futher drain.
If you are planning to rely on your car in the winter for a specific trip (e.g. daily commute) you need to take this into consideration. There are however ways to improve and mitigate this during the winter.
3. Driving mode and style
Electric cars have different modes (minimum of 2) which provide differing levels of regeneration. Instead of using the brakes to slow down the vehicle uses the braking effect of the electric motor, which then transfers power back into the battery. In this way you can maximise the amount of range available.
There will also be an ‘ECO’ (or similar) mode, which typically reduces the amount of power by limiting the throttle response. Disengaging the eco mode provides more performance, which you will probably need on the highway, but in urban/city environments most people will be quite happy cruising around in ECO.
As with any gas or diesel car, if you are really heavy on the accelerator and brake sharply you’ll find this reduces your range. But because electric cars are much smoother and quieter than gas/petrol cars you’ll most likely adopt a more relaxed driving style, which helps your range. Your EV display will show you how much power is going into the battery and you quickly learn to drive so that this is maximised. High speed continuous freeway / motorway driving also affects range.
4. Efficiency of the battery and motor system
All manufacturers are competing with each other for the most efficient car, but this isn’t something that is widely advertised. The EV equivalent to MPG (or l/100km) is miles per kW (m/kWh). The higher the number of miles, the more efficient it is, which means more miles from the same battery pack. And usually slightly better 0-60 times as well.
In general you can expect a worst case of around 2.5m/kWh (heavy footed fast driving in the depths of winter) to 5m/kWh best case (smooth driving in summer). Most car & driver combinations will fall into the 3.5-4m/kWh range. I’m ‘captain slow’ these days and we average 4.10m/kWh.