Most of the time you should only charge an EV to 80% because charging rates slow down dramatically past the 80% mark and because the long-term health of the vehicle's battery pack is improved when kept below 100%.

If you're above 80%, the car will slow the maximum charging power to avoid the cell voltages exceeding their limit (which would damage the battery).

So, charging from 10 percent to 50 percent capacity will be much faster than when charging from 80 percent to a full battery. Tesla's in-vehicle 'Supercharging Tips' indicates that a battery with 20 percent or less charge will charge at the maximum charge rate.