# The charging curve: why fast charging slows down as you fill up

> Why your car pulls a lot of power at a fast charger at first and then eases off, with worked examples and tips to lose less time on a trip.

Published: 2026-03-03 · Language: en · Source: https://laadpaalvinden.be/en/blog/charging-curve-fast-charging-slows/

You pull up to a fast charger with a nearly empty battery and the screen shows an impressive power figure. A little later it drops sharply, and towards the end the counter barely moves. That is the charging curve, and every electric car has one.

## What is a charging curve?

The charging curve shows how much power your battery accepts at each charge level. When the battery is low, it can take a lot of current. As the cells fill up, the car reduces the power to protect the battery.

In many cars the power stays high until roughly the halfway mark, then falls gradually. Above 80 per cent the difference is large. The shape varies from car to car, so the figures below are examples.

## Why does it slow down?

A nearly full battery tolerates less current. Force a lot into it anyway and the cells get hotter and wear out faster. Your car's battery management handles this for you.

## A worked example

Say your car has a usable battery of 60 kWh. Say it takes an average of 90 kW from 10 to 80 per cent, and an average of 25 kW from 80 to 100 per cent. These are assumptions to calculate with, not measurements of a real model.

- From 10 to 80 per cent is 70 per cent of 60 kWh, so 42 kWh. At 90 kW that takes 42 divided by 90 hours, about 28 minutes.
- From 80 to 100 per cent is 20 per cent of 60 kWh, so 12 kWh. At 25 kW that takes 12 divided by 25 hours, about 29 minutes.

So those last 12 kWh take as long as the first 42. At 18 kWh per 100 km they give you roughly 67 km of extra range, which is rarely worth the wait.

## Two short stops or one long one?

If you are planning a long trip, it often pays to leave earlier. Take the same car. Going from 10 to 100 per cent keeps you at the charger for about 57 minutes (28 plus 29). If you stop at 80 per cent and add another 12 kWh at a second charger, starting from a nearly empty battery, that takes about 8 minutes at 90 kW (12 divided by 90 hours). The same 12 kWh took 29 minutes at the end of the first stop.

Do count the detour and the plugging in and out. If the next charger is almost on your route, you save time. If it means a twenty-minute detour, you do not.

## What to do in practice

1. On the road, usually charge to about 80 per cent and then leave. Why that limit exactly is explained in [charging to 80 per cent](/en/blog/why-charge-to-80-percent/).
2. If you arrive with 50 per cent instead of 10, you already start at a lower power. If you have the choice, let the battery run down a bit further before you stop, as long as you can safely reach the next charger.
3. Leave as soon as you have enough range for the next leg, with a safe margin.

If there is a charger at your destination, for example at your hotel or at home, you do not need to charge to 80 per cent on the way. Then charge only what you need to get there.

## A warm battery charges faster

A cold battery accepts less power, and you notice that mostly in winter. Many modern cars can pre-heat the battery, sometimes when you set a fast charger as the destination in the car's navigation. That does not work on every car or in every navigation app. Check the manual or the settings to see what yours does.

If you do not have that function, driving for a while before you reach the charger helps. A battery that has just been driven for an hour usually charges more readily than one that sat in the cold overnight.

## When does this not apply?

- When charging with alternating current (AC), at home or at most ordinary public chargers, the charger built into your car mostly sets the power. You therefore see little of the curve. You can read more about the difference in [AC vs DC charging](/en/blog/ac-vs-dc-charging/).
- A charger can deliver less than your car can take. You always get the lower of the two. A 150 kW fast charger will not give more than the car allows, and a car that can take 150 kW will not reach that at a 50 kW charger.

## How do you see your own curve?

The manufacturer usually states the peak power, but not always the full curve. The peak says little about the waiting time: a car with a lower peak but a flat curve can finish sooner. While charging, look at your car's screen or your charging card's app to see how the power develops, and note the percentage and time a few times. After a few stops you know how your car behaves.

You can find more on the difference between kW and kWh in [charging speed explained](/en/blog/kw-vs-kwh-charging-speed/). Looking for a fast charger on your route? Browse all [fast chargers](/en/fast-chargers/) or check the [map](/en/map/).