Watch the power on a fast charger and you will see it change throughout the session. It rises quickly, holds high for a while, then falls as the battery fills. This pattern is called the charging curve.
Why the curve exists
A lithium-ion battery can accept energy quickly when it is low. As it fills, pushing energy in at the same rate would stress the cells and raise their temperature. The battery management system reduces the current step by step to protect the battery. Near the top, charging slows to a trickle while the cells are balanced.
What it looks like
| Battery level | Typical charging behaviour |
|---|---|
| Very low | Power ramps up |
| Roughly 10–50% | Usually the fastest charging |
| Roughly 50–80% | Power steadily falls |
| Above 80% | Much slower |
Every car has its own curve, and temperature changes it too.
How to use it
- On trips, arrive with a lowish charge and leave around 80%. You spend less time in the slow part.
- Charge to 100% only when the next leg needs it, ideally on AC at your destination.
- Make two short stops rather than one long stop if the route allows.
Going from 80% to 100% can take nearly as long as going from 20% to 80%. On a road trip, that last 20% is usually the most expensive time you spend.