When talking about how quickly an electric vehicle replenishes its battery, two different concepts need to be examined. The first is the maximum charging power, measured in kilowatts (kW), and the second is the charging speed, which measures how many miles of range are added in an hour.

Put simply, you can liken charging power to the rate at which water flows through a hose while charging speed is the rate at which it can fill a barrel. So, when talking about charging power, we’re referring to the rate at which energy is being transferred into an EV’s battery pack. The higher the power, the quicker the vehicle will charge, and the less time you will have to spend waiting for it to finish charging.

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Charging power and speed are connected but different

Charging power is how much juice an EV can put into its battery pack while charging speed is how quickly it can add miles of range.

Charging power is a straightforward concept (you get it by multiplying voltage and amperage), and manufacturers list this as one of the headline figures to help sell an EV. Even though most buyers rarely see the maximum advertised charging power because many conditions need to be met for it to be achieved, the fact that their vehicle can charge at, say, 350 kW will help seal the deal and ensure charging station bragging rights.

The fastest way to charge an EV is by using a Level 3 DC (direct current) fast charger, whose power typically ranges between 50 and 350 kW. You can find this type of charger only at a public charging station, and you can’t have one installed in your garage because its power requirement is very high, it needs a strong electrical connection to the grid, and it’s very expensive.

You can install a Level 2 AC (alternating current) charger, though, whose power rating ranges from about 3 kW to 19.2 kW (or 22 kW in Europe). For anything over 11 kW, you will need a special three-phase electrical connection, which isn’t cheap to install, and your local electricity grid may not even be able to support it. But even a 7 kW charger is enough for an overnight top-up.

Charging speed is not as simple to calculate as power because it depends on several factors. The most important factor is charging power, but the size and state of charge of the battery pack being charged are also important. The EV’s battery thermal management system and outside temperature and battery temperature also play a role in how many miles of range can be added in an hour.