Energy comes first
For a simplified estimate, multiply usable battery capacity by the desired change in charge percentage. A 60 kWh battery moving from 20% to 80% needs approximately 36 kWh added.
Turn energy into time
Divide the energy supplied by the average charging power. Allow for losses: at an assumed 90% efficiency, 36 kWh added requires about 40 kWh supplied. At a constant 7 kW, that is roughly 5.7 hours.
Why reality varies
Power may change with battery temperature, state of charge, the vehicle and the available supply. Charging commonly slows as the battery fills. Use the vehicle’s estimate for a journey plan; the calculator below is for learning.
Further reading: Official energy guidance ↗