Automotive Research

How EV charging works & what you need to know

As electric vehicles grow in popularity, it's becoming more important to understand how to charge them at home and on the road.

A few key concepts are all you need to know to navigate EV chargers and estimate your charge times like a pro. 

How electricity is measured

  • Kilowatts: Electrical power is measured in watts, with a kilowatt (abbreviated kW) being equal to 1,000 watts. EV charging speeds are measured in kW. The more kW, the faster the charger.
  • Kilowatt-hours: A kilowatt-hour (abbreviated kWh) is equal to 1 kilowatt of power delivered for 1 hour. You've likely seen kWh metered out on your electric bill. EV chargers use kWh the same way gas pumps use gallons to measure gas. 
  • Miles per kilowatt-hour: Where gas cars use miles per gallon (MPG) to describe efficiency, EVs use a similar metric called miles per kilowatt-hour (mi/kWh). Sometimes this number is converted into miles per gallon equivalent (MPGe) to allow direct comparison between gas and electric vehicle fuel efficiency.

Understanding EV charging speeds

Charging speeds are measured in kW, and the quantity of charge that is delivered is measured in kWh. For example, a 50 kW fast charger can deliver 25 kWh of energy in a half-hour, whereas a slow 2 kW charger would only deliver 1 kWh in the same period.

To simplify things, chargers are divided into 3 broad categories:

Level 1 chargers are portable and can be carried inside the vehicle to charge wherever a standard household outlet is available.

Level 1

Charge rate: 1 to 2 kW

Typical range added per hour: 2 to 5 miles

Level 1 chargers often come with an EV when you buy it. They plug into standard 120-volt household outlets and are meant to be easily portable, requiring no installation.

For those who drive less than 50 miles daily, Level 1 charging at home every night may be enough to provide a full charge each morning. Adding more range can take a very long time on Level 1, though, with a full charge from empty potentially taking days. Those who consistently drive more may be better served by a Level 2 home charger.

Level 2 chargers are usually installed, either hardwired or with a NEMA outlet, at a home or a public charger.

Level 2

Charge rate: 3.3 to 19.2 kW

Typical range added per hour: 10 to 35 miles

Level 2 chargers operate on a 240-volt source, either hardwired or on a NEMA outlet like household appliances use. Level 2 chargers are available publicly and can also be installed at your home.

While Level 2 chargers can charge anywhere from 3.3 to 19.2 kW, most modern ones are rated between 6 and 12 kW. That's enough to refill most EV batteries overnight, though slower Level 2 chargers may not be able to refill larger batteries completely.

During the day they're best used as destination chargers at places where you'll be spending at least a few hours, such as a restaurant or mall.

Common Level 2 charger speedsTypical range added per hour1
3.3 kW11 miles
6.6 kW23 miles 
7.2 kW25 miles
9.6 kW34 miles
11.2 kW39 miles

1For a hypothetical EV that gets 3.5 mi/kWh. Different EVs will see different amounts of added range per hour depending on their efficiency.

ADVANCED TIP: Range added per hour differs by vehicle

People often talk about range added while charging, versus kilowatt-hours. It’s more intuitive, after all. But remember that miles added while charging depends on how efficient your EV is.

If 2 EVs both add 20 kWh at a charger, but one has an efficiency of 2.5 mi/kWh and the other has an efficiency of 4 mi/kWh, then the first will add 50 miles of range and the second will add 80 miles.

Level 3 DC fast chargers are only found at public charging stations.

Level 3 (DC fast charging)

Charge rate: 50 kW to 350 kW

Typical range added per hour: 180 to 240 miles

Level 3 chargers, also known as DC fast chargers, run at 480 volts or higher and are currently only available at public charging stations. Capable of adding up to 10 miles of range per minute, they’re the chargers that make longer-distance EV trips practical. All Tesla Superchargers are Level 3. 

Not all EVs can use DC fast chargers, and those that can aren’t always able to accept the charger’s highest rate of charge.

Common Level 3 charger speedsTypical time to charge from 10% to 80% 
50 kW60 minutes 
100 kW45 minutes 
150 kW30 minutes 
350 kW20 minutes 

Though Level 3 chargers have high outputs, EVs typically only charge at their fastest on Level 3 when their batteries are mostly empty. At higher charge levels, Level 3 charging slows down to avoid excessive battery heat.

This is known as the "charging curve." The specifics of your vehicle's charging curve will depend on its programming and a few other factors, such as ambient temperature and whether your battery is already warm when fast charging begins. 

It may take your EV as long to charge from 80% battery to 100% battery as it does to charge from 10% to 80%. Thus, on an EV road trip, it saves time to charge at DC fast chargers only when your battery is running low, and then depart after reaching 80% charge.

Charging rate vs. acceptance rate

Just as chargers differ in how quickly they can deliver charge to an EV, EVs differ in how quickly they can accept charge. The highest rate at which an EV can charge is known as its “acceptance rate.”

When a charger’s maximum speed and an EV’s acceptance rate differ, the EV will charge at the lower of the 2 speeds.

Charging station ratingEV acceptance rateActual charging speed
9.6 kW7.2 kW7.2 kW
9.6 kW9.6 kW9.6 kW
9.6 kW11.2 kW9.6 kW

This is most important for Level 3 charging, where there is a lot of variance in acceptance rates. Some EVs have a Level 3 acceptance rate as low as 50 kW, while others go as high as 350 kW. This can be the difference between a 10%-to-80% charge taking an hour or taking 20 minutes. 

Level 2 acceptance rates also vary. Many plug-in hybrids only have a 3.3 kW acceptance rate since they have relatively small batteries. Full battery electric vehicles typically have a Level 2 acceptance rate of at least 6.6 kW, with newer models offering a 9 to 12 kW acceptance rate.

In practice, this is a small difference—a car that can charge at 6.6 kW might add 23 miles of range in an hour of Level 2 charging, compared to 34 miles for a car charging at 9.6 kW.

Understanding EV charging connectors

In North America, there are 3 main types of EV plugs:


Also known as the “J-plug,” this is the current standard Level 1 and Level 2 connector for all EVs in the U.S. other than Teslas.


Short for Combined Charging System, this plug is essentially a larger version of the J1772 plug and is used for Level 3 DC fast charging. In the U.S., almost all non-Tesla EV models use CCS for Level 3 fast charging.


Often referred to as the “Tesla plug” but now officially known as the North American Charging Standard, this connector is used by all Tesla models for all charging, whether Level 1, 2, or 3.


Many other automakers have announced plans to adopt the NACS connector in their future cars, moving away from the J1772 and CCS standards.


While common in Japan, this Level 3 charging plug is only compatible with a few vehicles in the U.S.

Which connector can you expect on which vehicles?

Non-Tesla EVs:

  • All use J1772 for Level 1 and 2 charging. 
  • The vast majority will use CCS for Level 3 charging. A few (most notably the Nissan Leaf) use CHAdeMO.
  • In addition, there are aftermarket converters that allow J1772/CCS-standard EVs to use Level 1 and 2 Tesla NACS chargers. 

As of 2023, non-Tesla EVs cannot use the vast majority of the Level 3 Tesla Supercharger network, even with a converter. The exception is a small number of Supercharger locations that have an integrated NACS-to-CCS converter called Magic Dock, mostly in New York and California. These can be identified in the Tesla app.

Tesla EVs:

  • All use the NACS connector for Level 1, 2, and 3 charging.
  • Aftermarket converters allow Teslas to use J1772 and CCS chargers as well.

Finding & using chargers

Whether buying a home charger or looking for a public charger, knowing what plug your EV uses and how fast it can charge (the acceptance rate) lets you pick the right one for your needs. 

Home chargers

When buying a home charger, you'll want a model that has the right plug for your EV and that can provide charge or near your EV's acceptance rate. Home chargers are often marketed by their amperage rather than charging speed in kW.

Before having a charger installed, find out what amperage is available in your garage. If there's already a sufficient circuit, you'll want a charger that doesn't exceed 80% of its amperage (e.g., a 40-amp charger for a 50-amp circuit). If you need to have a circuit installed or upgraded, you'll want to know how many amps it should have. 

Charger amp ratingCharger maximum speedMinimum electrical circuit amperage needed
16 amps3.8 kW20 amps
24 amps5.7 kW30 amps
32 amps7.6 kW40 amps
40 amps9.6 kW50 amps
48 amps11.5 kW60 amps

It's easy determine a Level 2 home charger's kW speed by multiplying its amperage by 240 volts. For example, a 40-amp charger will have a maximum charging speed of 9.6 kW (240 volts x 40 amps = 9,600 watts). 

RELATED: A how-to guide to buying a home EV charger

Public chargers

Public charging stations advertise their available chargers by plug type and kW charging speed. This makes it easy to find a compatible charger as well as estimate how long you need to charge, or how much range you can expect to see for a given charging session.

There are a few different tools for finding public chargers:

  • Charging network apps: Most public chargers are part of a major charging station network such as EVgo or ChargePoint. Each of these networks has a mobile app so you can find their stations, and see if they're out of service or currently in use. 

Save on charging with EVgo: AAA members save on EVgo standard charging rates, with no monthly membership or session fees.

Learn more and save on EV charging

The PlugShare app lists public charging stations across all major networks and is widely used as a one-stop resource for finding charging locations. | Image courtesy of PlugShare

  • PlugShare: This free app bills itself as "the most accurate and complete public charging map worldwide." It lists charging stations from all the major networks, as well as non-network public chargers at destinations like hotels.
  • In-car navigation: Many EVs have built-in mapping that shows charging stations and can estimate how long you'll need to charge for a given distance.
  • Search engines: Tools like Google and Google Maps are increasingly including EV station information on the go. 

Save on charging with EVgo

AAA members save on EVgo standard charging rates, with no monthly membership or session fees.


Learn more about EVs in the AAA Car Guide

The annual AAA Car Guide can help you find the perfect car, with rankings based on fuel efficiency, handling, and more. 

Looking for a dealer you can trust?

AAA members can enjoy a great car buying experience with AAA Car Buying Service. Find the car you want from a certified dealer and feel confident in the price you’re paying.

AAA Car Buying Service is only available to AAA members. Outside of Southern California, AAA Car Buying Service is managed by TrueCar, Inc. Only car buying research tools are available in Hawai‘i.

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