The charging curve, explained
A charging curve is a graph of the maximum power an EV can accept at each state of charge. It's the single most useful piece of information for predicting how long a session will actually take — and it's the piece most calculators ignore.
How to read a charging curve
The x-axis is state of charge (0% empty, 100% full). The y-axis is power in kW. The line shows the most the car will pull at that SOC, assuming the charger can supply it and the battery is at the right temperature.
In a session, the actual delivered power is the lower of: the charger's max kW, the car's onboard limit, and the curve at the current SOC. The session lives along whichever line is lowest.
Three curves, three very different EVs
Kia EV6 — 800V, peak 240kW
Holds 220kW+ from 10% to 40% SOC, then tapers gradually. This is what an 800V architecture buys you: a long, flat-topped curve that uses 350kW chargers properly.
Volkswagen ID.3 — 400V, peak 175kW
Peaks at 175kW around 10% then tapers steadily. A 350kW charger gives no benefit over a 175kW one for this car.
Nissan Leaf — CHAdeMO, peak 50kW, passive cooling
A 50kW ceiling that drops further once the battery warms up over consecutive sessions. The lack of liquid cooling shows here.
What the curve tells you about your car
- Best stop window: arrive at the lowest SOC you're comfortable with (typically 10–20%) and end at the SOC where the curve drops below 50% of peak.
- When to upgrade the charger: if your car peaks at 100kW, a 150kW charger is wasted. If it peaks at 250kW with a wide flat top, only a 250kW+ charger captures it.
- Cold weather hit: below 10°C the entire curve scales down 20–30% on cars without battery pre-conditioning.
Want to see your own car's curve at a specific charger speed? Open the time calculator.