A charger’s advertised power is not a promise that your EV will receive that power throughout a stop. To compare charging times meaningfully, ask how much energy was added, over which battery-percentage range, and under what conditions.
Start with kW and kWh
Kilowatts (kW) describe power: the rate of energy transfer. Kilowatt-hours (kWh) describe an amount of energy. Confusing the two makes charging claims difficult to compare.
A useful calculation is:
Time in hours = energy added in kWh ÷ average charging power in kW.
This calculation needs an average over the session. Substituting an advertised peak can produce an unrealistically short estimate.
An illustrative 30-minute calculation
Imagine a battery with 70 kWh of usable capacity. Moving from 20% to 80% represents 60% of that capacity:
- 70 × 0.60 = 42 kWh added.
- If average power into the battery were 84 kW, 42 ÷ 84 = 0.5 hours, or 30 minutes.
- At an average of 60 kW, the same simplified calculation gives 42 minutes.
These are invented, round-number scenarios for explaining the arithmetic, not measured performance of a vehicle. They assume a simple relationship between displayed battery percentage and usable energy and exclude queues, connection time, and other overhead. Charger-meter energy can also differ from energy stored in the battery.
Why power changes during a stop
The Australian Government’s charging-equipment guide explains that charging rates depend on the vehicle, battery condition, and existing charge level. Charging can slow as the battery approaches full charge. For AC charging, the vehicle’s onboard charger also matters; DC fast charging bypasses it.
Consequently, a high peak reached briefly tells you less about a full stop than the average over a stated charging window. Do not compare a 10–80% claim directly with a 20–80% claim as though the energy added were identical.
Compare the complete stop
Ask for the battery window, usable capacity, charger conditions, and vehicle configuration behind a quoted time. Follow the vehicle manufacturer’s preparation and charging instructions, particularly where conditions differ from the advertised test.
The Australian Government’s practical charging guide advises checking charger compatibility, location, and possible idle fees. It also notes that charging beyond 80% can be slower and recommends consulting the vehicle’s own instructions.
An 80% stopping point is therefore a planning consideration, not a universal rule. Your route may require more energy, and the manufacturer’s instructions take precedence.
Budget for the whole stop
Consider a hypothetical session that delivers 30 kWh in 20 minutes. The average delivered power during that session is 90 kW: 30 divided by one-third of an hour. If waiting takes 10 minutes and connection and payment take another 5, the total stop is 35 minutes. Those extra minutes change the journey plan without changing the session’s average charging power.
These are invented figures for arithmetic, not measured results from a vehicle or network. Record queue time, setup time and charging duration separately when comparing your own stops. Do not describe energy divided by the entire visit duration as the charger’s measured session power.
For the money side of the same stop, use our public charging cost checklist to account for applicable fees. Time and cost are separate comparisons.
Use a consistent comparison
Write down four things for each vehicle: energy added, charging window, elapsed time, and test conditions. If one is missing, describe the comparison as incomplete instead of declaring a winner from the biggest kW number.
The underlying arithmetic applies internationally. Connector standards, electricity supplies, tariffs, and equipment labels vary by country; verify them locally. Explore more ownership guidance and EV coverage.
