Charge an EV to the same percentage on two different days and the dashboard can show two different range numbers.
Nothing necessarily went wrong with the battery.
The number on the screen is an estimate of how far the car thinks the remaining energy might take you.
The car has to make assumptions
A battery stores energy, not miles.
To turn the amount of energy remaining into a range prediction, the car needs to assume how quickly that energy will be used.
Many cars use recent consumption, temperature and other information when making that prediction.
If your recent driving has been fast motorway work in cold weather, the estimate may fall. After slower efficient journeys in mild weather, it may rise again.
This is why people call it the guess-o-meter
The nickname is slightly unfair because the car is doing a real calculation, but it captures the point: the figure is a forecast.
It is not the same thing as measuring the battery's energy capacity.
Look at percentage and consumption as well
For a journey you know well, battery percentage used can be more informative than watching the predicted miles change throughout the trip.
That is also why MyEVRange asks drivers for:
- miles travelled;
- battery percentage at the start;
- battery percentage at the end.
From those three values we can calculate an equivalent full-battery range without relying on the dashboard prediction.
See how MyEVRange calculates a journey.
A falling prediction does not automatically mean battery degradation
Cold weather, recent motorway driving or towing can all pull the forecast down. If the car then returns to easier conditions, the estimate can rise again.
A permanent battery-health issue needs better evidence than one pessimistic range prediction on the dashboard.
