This also means that energy can be expressed as power times time, like the kiloWatt-hours used to express the electric energy your house consumes during a billing period. Another common measure of energy is the Joule. A Watt (a unit of power) is one Joule per second. A kiloWatt-hour is therefore 3.6 MJ.
It means the battery inside your electric car can store a maximum of 40 units, or kWh, of electricity. In other words, kWh for an electric vehicle is a measure of how much electricity can be stored inside the battery. If you had an 80 kWh battery in your car, you would be able to store twice as much electricity as a 40 kWh car.
The larger the battery capacity (more kWh), the longer the EV can run before needing to be recharged, meaning a greater “fuel tank” or range. While kWh is a unit of energy, a kilowatt (kW) is a unit of power. Power refers to the rate at which energy is used or, in other words, the speed at which work is done.
Fully electric cars and crossovers typically have batteries between 50 kWh and 100 kWh, while pickup trucks and SUVs could have batteries as large as 200 kWh. Of course, a larger battery will take longer to charge than a smaller battery, and it will cost you more in electricity to do so.
Assuming the car battery is completely empty, it will take just over 13 hours to charge it to full capacity. The calculation is: 40 kWh divided by 3 kW = 13.3 hours. Assuming the car battery is completely empty, it will take just under 6 hours to charge it to full capacity. The calculation is: 40 kWh divided by 7 kW = 5.7 hours.
Let’s say you have an electric motor rated at 200 kilowatts (kW) at peak power output. If you ran that motor for 30 minutes you would use 100 kWh of energy — 200 multiplied by 0.5 (of an hour) equals 100 kWh. If how far your electric car can travel on one charge is important to you, as a general rule of thumb, you want an EV with a big battery.