Kilowatt-hours
Battery capacity is measured in kilowatt-hours, or kWh. This is very different from the way gasoline is measured, in gallons, because it doesn't have anything to do with weight or volume, but with how much actual energy is available. Usually, kWh is used as a measure of work. You see it most commonly on your utility bill, where it indicates how much power you used.
For example, a 300-watt space heater would need to run for just over three hours to use 1 kWh, while a 60-watt lightbulb would need to run for more than 16 hours. The average American household uses about 30 kWh a day.
The efficiency of electric cars is best measured as the number of kWh it takes to travel 100 miles, or kWh/100 miles. Just like on a gas car, more "fuel" doesn't always mean more range; efficiency plays a major role as well.
It's important to note that charging speeds use kilowatts, not kWh. A watt measures the rate at which energy flows; a kWh is a way to measure how much energy has flowed.
Voltage: 400 volts vs. 800 volts
Different electric car platforms are capable of handling different voltages. By increasing the voltage, you can increase the power (wattage) without increasing the amount of current (amperage). This means less heat, less need for cooling, lighter-weight components and more efficiency. One of the most important advantages of EVs with 800-volt architecture is faster charging … assuming you can find a powerful enough charging station.
For the most part you'll see 400-volt or 800-volt cars, although there are a few outliers. The Lucid Air uses suspiciously specific 924-volt architecture. Some vehicles, like the Hummer EV, use 400 volts for driving and 800 volts for charging. Some have variable limits, like the Porsche Taycan, which can temporarily charge at up to 1,000 volts.
Ultimately, the higher voltage systems offer weight savings and improved performance but come with a higher price tag.
Power inverter
Batteries require direct current (DC) to charge, and they release stored energy as direct current. But the power that comes from your wall socket for Level 1 or Level 2 charging is alternating current (AC). The motors in electric cars run on alternating current (and recapture energy as alternating current) since alternating current lets them provide more torque and more consistent operation regardless of conditions.
Power inverters convert DC to AC and vice versa — although they do much more than that. That means they're a necessary component for driving your electric car and for charging it at home. They convert energy coming from the battery to a form that's usable by the electric motors, and they convert energy recaptured by the motors, or energy coming from a Level 1 or Level 2 charging station, into a form that's usable by the battery.
Inverters are also capable of adjusting the frequency and amplitude of their output, which allows them to control the power and speed of an electric car's motors. Alternating current comes in pulses, and when the inverter converts DC to AC it can control the frequency and amplitude (think, strength) of the pulses it outputs. Increasing or decreasing the frequency of the pulses increases or decreases the speed at which the motor turns, and increasing or decreasing the amplitude of the pulses increases or decreases the torque the motor generates.