A metric used when comparing how fast electric vehicles charge is range replenishing speed. This is usually measured in the average amount of range gained per minute while charging from 20 to 80 percent.
The first I heard of range replenishing speed was from InsideEVs. They have great fast-charging analysis on many electric vehicles with a wide range of metrics used and is currently the best (only?) place to find tests measuring this metric.
Pro: Simple and familiar
While perhaps not as simple as just time, it is also relatively simple and familiar to understand a rate over time.
Time and distance are both familiar concepts that we use in other parts of our lives. Understanding how much distance is gained over time is an additional, but subjectively simple step.
Pro: Efficiency is taken into account
Two vehicles that charge at the same power for the same amount of time will have the same amount of energy added. This energy will result in a different amount of range for each vehicle depending on its efficiency.
This metric is simply the average charging power multiplied by the vehicle’s efficiency.
Pro: Battery size does not matter
Compared to some other metrics, the size of the vehicle’s battery does not matter and is taken into account.
This means you do not need to look at battery size in addition to this metric when evaluating a vehicles charging experience.
Pro: Easier to compare to other fuels
Some other metrics are measured in kilowatts (kW) and are very specific to electric vehicles. These can be useful when comparing electric vehicles to each other, but not so useful when comparing to other types of fuels.
It may not be as easy as time, but replenishing speed could be compared to other fuels and not just electricity.
Con: Does not capture the complexity of charging curves
There are many variables that affect how much power an electric vehicle receives at a given time.
Some vehicles have a fairly [linear curve], with power being higher at a lower state of charge. Other vehicles have a [weird, non-linear curve] that is much less predictable. With these different curves, arriving at a charger with the same state of charge could result in very different charging experiences for different vehicles.
This metric has the same downfall as average charging power and does not capture this complexity.
Con: Efficiency is difficult to predict
There are several standards around the world for determining the efficiency and range of vehicles. No matter the fuel type, efficiency depends on a number of variables that are difficult to test and control across all vehicles.
Since replenishing speed depends heavily on efficiency, it shares all of its unpredictability as well.