If you read about EV chargers for long, you will see two abbreviations that look almost identical: kW and kWh. They measure different things, and mixing them up is one of the most common sources of confusion when choosing a home charger. This article explains each unit with simple examples.
What a kilowatt (kW) measures
A kilowatt is a unit of power, which is the rate at which energy flows. A charger rated at 9.6 kW can deliver energy at up to 9.6 kilowatts at any moment. Think of power as the width of a water pipe. It tells you how quickly water can move, not how much water is stored.
What a kilowatt-hour (kWh) measures
A kilowatt-hour is a unit of energy. It is the amount of energy delivered by one kilowatt of power running for one hour. A battery's size is usually stated in kWh, so a 75 kWh battery can hold 75 kilowatt-hours of energy. Think of energy as the amount of water in the tank.
Putting the two together
Charging time is roughly the battery's energy divided by the charger's power. The formula is:
Charging time (hours) = battery size (kWh) / charger power (kW)
Using round numbers, a 75 kWh battery on a 9.6 kW charger needs about 7.8 hours to go from empty to full, before losses. On an 11.5 kW charger, the same battery needs about 6.5 hours. Real sessions take a little longer because some energy is lost as heat during conversion, and because charging usually slows as the battery nears full.
Reading electricity bills
Utility bills also use kWh, but there it measures the total energy used over a billing period. Each kilowatt-hour your car draws from the grid is one more kilowatt-hour recorded on your meter. This is a separate question from how fast the charger works, so a charger's kW rating does not tell you what it will cost to run.
Common mistakes
- Comparing a charger's kW rating with a car's kWh battery size as if they were the same unit.
- Assuming a higher kW rating always means a faster charge. The car's onboard charger can limit the rate.
- Forgetting that a kWh figure describes how much energy is stored or used, not how fast it moves.
How this applies to EVIQO chargers
EVIQO rates its chargers in kW, all on 240-volt circuits. A 40-amp charger is rated at 9.6 kW, and a 48-amp charger is rated at 11.5 kW. Use these kW ratings to compare chargers. Use your car's battery size in kWh to estimate how long a full charge takes. Every EVIQO charger includes a 25 ft cable and a 3-year warranty, and a 4-year extended warranty is available for an extra charge.