Plug into a fast charger at 15% and you may see high power for a while, then a steady drop as the battery fills. Past about 80%, charging can slow to a crawl. This shape is called the charging curve, and every EV has one.
Why charging slows down
Think of filling a crowded bus. When it is empty, people get on quickly. As it fills, everyone has to squeeze in, and boarding slows. Inside a battery, lithium ions move into the electrode material; as it fills, there is less room, and pushing in more at high power would raise heat and stress. The car's battery management system deliberately lowers the current to protect the battery.
A typical shape
- Low battery (about 10–50%): highest power, close to the car's maximum.
- Middle (about 50–80%): power gradually falls.
- High (above about 80%): power drops steeply until the battery is full.
Exact numbers vary by car, battery temperature and charger.
What it means for your trips
- Getting from 20% to 80% often takes about as long as going from 80% to 100%, or less.
- Two short stops can be quicker than one long stop to 100%.
- Arriving at 10–20% gives you the fastest part of the curve.
Other things that affect speed
- Temperature: a hot or cold battery charges more slowly.
- Your car's maximum power and the charger's output.
- Power sharing with another car at the same station. See why your car charges slower.
Good charging etiquette
At a busy fast charger, unplugging at 80% frees it for the next driver and saves you time. See charging etiquette.