What Is an EV Charging Curve?

An EV's charging curve is the shape of how fast it charges over time: rising quickly at the start, peaking somewhere in the middle, then tapering off as the battery approaches full. Charging speed is never a flat, constant number, regardless of the charger's rated power.

Why the Curve Isn't Flat

Batteries accept charge fastest in the middle state-of-charge range, roughly 20-70%, and slow down deliberately as they approach full to avoid excess heat and long-term cell damage. A 400 kW DC fast charger might only deliver a fraction of that power once a battery passes 80% state of charge, no matter how much power the charger itself can supply.

What This Means in Practice

Two chargers with very different peak power ratings can end up delivering similar energy in the final stretch of a charge, because the battery, not the charger, becomes the bottleneck. This is why real-world charging time from empty to full doesn't scale linearly with charger power the way a simple kWh-divided-by-kW calculation would suggest.

Why It Matters for Depot Scheduling

Fleets planning opportunity charging windows should plan around the energy actually deliverable in that window, not the charger's headline power rating. A short mid-shift top-up charging from 20% to 60% will be much faster per kWh than the last stretch from 80% to 100%, which matters when scheduling tight turnaround times between routes.

Neutron's Perspective

Understanding the charging curve is part of how we size Fleet DC Charging installations correctly, planning around real achievable charge times rather than theoretical maximums that batteries can't actually sustain.

Why does charging slow down near a full battery?

Lithium-ion cells can't safely accept high current once they're nearly full without risking excess heat and long-term degradation, so the battery management system deliberately tapers the charge rate as state of charge rises, regardless of how powerful the charger is.

How should fleets plan around the charging curve?

Plan charging windows around the energy actually delivered in that time, not the charger's peak power rating. A 30-minute session on a 400 kW charger won't deliver 200 kWh if the battery tapers well before then, which matters when scheduling vehicles for opportunity charging between routes.