EV Charging Curve Explained: Average, Not Peak

The shape of the curve

Plot charging power against state of charge and you get a shape, not a line. Power typically rises quickly from a low state of charge, holds a plateau for a while, then tapers — sometimes gently, sometimes in abrupt steps — until it is a trickle near full.

The advertised figure is the highest point on that shape. It may be sustained for two minutes or twenty, and the specification sheet does not say which. That omission is the reason an EV charging curve explained by peak figure alone is close to useless. That single omission is why an EV charging curve explained properly is more useful to a buyer than any peak kilowatt number.

Average power is the number that matters

What determines how long you stand in a car park is the average power across the range you actually charge. Work it directly:

Two cars can share an identical 350 kW headline and sit in different rows of that table. The useful published metrics are 10–80% charging time in minutes and miles added in ten minutes, because both are averages over a real range rather than a peak at a single instant.

Why the taper exists

The taper is not a defect. Pushing high current into a nearly full lithium cell raises voltage and heat and accelerates degradation, so the battery management system reduces power as the pack fills. It is the car protecting the most expensive component you own.

Three factors move the curve on any given day:

• Battery temperature. A cold pack charges slowly until warmed, which is why preconditioning — heating the battery en route to a charger — is worth more in winter than a faster charger is.
• State of charge on arrival. Arriving at 10% puts you in the fast part of the curve; arriving at 50% skips it.
• Cooling capability. Sustained high power generates heat, and a pack that cannot shed it will derate. This is why repeated fast charges on one journey are slower than the first.

Efficiency changes the answer again

Charging speed in kilowatts measures energy per hour. What you care about is miles per hour of charging, and that depends on how far the car goes on each kilowatt-hour.

A car averaging 100 kW at 4 miles per kWh gains 400 miles of range per hour of charging. A car averaging 150 kW at 2.5 miles per kWh gains 375 miles per hour — less, despite charging 50% faster in raw power terms. Efficiency and charging speed multiply, and reviews that report only one of them are reporting half the calculation.

Why two cars with the same pack size differ

Architecture and chemistry move the curve before any of the day’s conditions do.

Pack voltage. Higher-voltage architectures move the same power at lower current, which generates less heat and allows a flatter plateau for longer. That is why some cars hold high power well past the halfway mark while others begin tapering early.

Cell chemistry. Lithium iron phosphate cells tolerate being charged to 100% and are often recommended to be filled regularly for state-of-charge calibration, but their flatter voltage profile makes charge estimation harder and their cold-weather charging is typically worse. Nickel-based chemistries carry higher energy density and prefer to live between roughly 20 and 80%.

So an EV charging curve explained for one model does not transfer to another with a similar-sized battery. Check the specific car.

How to read a published curve

Independent testers publish charging curves as graphs, and there are four things to check before trusting one.

1. Was the battery preconditioned? A cold-start curve and a preconditioned curve are different tests of the same car.
2. What was the charger’s capability? A curve is capped by the station; a 150 kW station cannot reveal a 250 kW peak.
3. Ambient temperature. Curves measured in summer and winter differ substantially.
4. Was it the first charge of the day? Heat-soaked packs from repeated stops perform worse.

A test that documents all four is comparable to another test that documents all four. One that documents none is an anecdote.

What it means in practice

The behavioral consequences are simple and they save real time. Charge 10–80% rather than to full on any journey with another stop available, because the last 20% frequently takes as long as the first 50%. Arrive lower rather than higher. Precondition whenever the car offers it. And treat two short stops as faster than one long one, which is counterintuitive until you have seen the shape of the curve.

At home, none of this applies — overnight AC charging is flat and slow by design, and charging to 100% there is fine unless the manufacturer advises otherwise for daily use.

The checklist

• Ignore peak kW. Look for 10–80% time and miles added in ten minutes.
• Multiply charging speed by efficiency to get miles per hour of charging.
• Check the test conditions on any published curve before comparing it to another.
• Precondition the battery before every fast charging stop.
• Stop at 80% when another charger is within range.
• Expect slower second and third stops on a long day; that is heat, not a fault.

With the EV charging curve explained this way, the specification that sells cars turns out to be the one that predicts your day least well — and the two numbers that predict it best, average power and efficiency, are the ones you have to go looking for.