Why your electric car is charging slower than you expected

In this article, we’ll explore some of the reasons behind varying charging speeds and offer ten practical tips and tricks on how you can optimise the charging process.

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My electric car is not charging at the speed I thought it would.

Many of us have made similar observations about our electric vehicle (EV) on one or several occasions. If your car’s charge speed seems too low, the next step is understanding what the reason might be – and how to fix it.

Maximum kW differences

Lower EV charge speed is sometimes due to a difference between car charging capacity and charger maximum power output.

Home charging stations typically have outputs of 7, 11, or 22 kW. A kW is short for kilowatt. It measures the flow of electrical current and is used to state the maximum power output of a charging station and charging rate of an EV. If there is a difference between the two, the charging speed is restricted by either the car or the charger.

For example, consider a Hyundai IONIQ 5 with an 11kW maximum charge rate. If you attach it to a 22kW charger, it will still only charge at a max of 11kW.

Let us imagine that you attach three identical Hyundai Ioniq 5 cars with a 77.4 kWh battery capacity. We plug them in with empty batteries to a 7.4 kW, a 11 kW, and a 22 kW charger, respectively.

Your time to full charge would be:

  •       Around 12 hours for the 7.4kW charger
  •       Around 8 hours for the 11kW charger
  •       Around 8 hours for the 22kW charger

Please note that are many other electrical details that can affect charging speed. 

See here for an overview and a good way to calculate your likely charge speed. 

Battery State of Charge

Battery State of Charge (SoC) can influence charging speeds, sometimes causing an electric car to charge slower. SoC essentially represents how close to fully charged your car battery is in percentages.

Unlike gas-powered vehicles that refuel at a consistent rate, electric vehicles equipped with lithium-ion batteries see varying charging speeds based on their SoC. EV batteries tend to charge faster at lower SoC (e.g., 20%) compared to higher ones (e.g., 80%). As a result, charging an EV from 0 to 80 percent can be quicker than charging it from 80 to 100 percent.

This charging pattern is not only a result of battery chemistry but also serves as a protective measure to prevent overheating and preserve the battery. Some EV manufacturers advise against regularly charging their EVs above 80 percent.

Battery temperature

Battery temperature plays a crucial role for charging speeds. EV batteries operate most efficiently around 20°C. Most EVs are equipped with a Battery Management System (BMS) that monitors and adjusts charging based on temperature. If temperatures deviate significantly from 20°C, the BMS reduces charging speed to protect the battery.

Seasonal changes also impact charging times. For example, cold weather can lead to longer charging times, although pre-heating the car can help speed up charging in colder weather.

Charging in hot weather doesn’t impact charge speeds as significantly as cold weather, but can still pose challenges. The primary concern here is battery overheating. If there is a risk of overheating, the BMS system may reduce charging speeds and increase cooling to maintain optimal temperature levels.

Using your car while it charges

You might not even think that using a car while it’s charging has any impact, but in fact, it can visibly add to the charging time, depending on how it’s used.

While you obviously can’t drive a car while it’s plugged in, staying inside the vehicle and using heating or air conditioning, the sound system, or lights, for example, can increase energy consumption and divert some of the energy from charging, adding to charging times.

Software or hardware issues

Although most software updates can significantly improve electric car charging and increase the charging speed, the opposite might occasionally occur. In such cases, it can often be difficult to uninstall updates, and you may have to deal with the problem until the new software update nullifies the issue.

On the hardware side, EV batteries can cause issues over time. However, with a lifespan of up to 10-15 years, they can sometimes outlast the vehicle. That said, batteries do age and lose some of their capacity in the process. As they age, the resistance inside batteries also increases. This means that the power they can accept decreases, slowing down the charging rate.

It’s worth noting that EV batteries are often designed with an excess capacity to act as a buffer against aging.

How can you increase charging speeds?

To increase your electric car’s charge speed, consider the following strategies:

  1.   Optimize battery temperature: Pre-heating the battery or arriving at a charger with optimal battery temperature can help increase charging speeds. Additionally, consider parking your car in a temperature-controlled environment.
  2.   Upgrade your charger: Switch from a level 1 charger to a level 2 charger for faster charging. Level 2 chargers can provide a lot more kilomters of charge per hour, adding range to your car 3 to 5 times faster than level 1 chargers.
  3.   Choose a mild temperature zone: Park your car in an area with mild temperatures before charging, as extreme cold or heat can impact charging speeds.
  4.   Warm up batteries before fast charging: Warming up the batteries before fast charging can help reduce charging time. However, this may not make a difference when using a level 2 charger.
  5.   Future-proof your charging setup: Install a charger with higher capacity than you currently need.
  6.   Use heavier-gauge wire: When installing a new circuit or pulling new wires for an EV charger, opt for heavier-gauge wire.
  7.   Consider adjustable current chargers: Some chargers, like Tesla’s Wall Connector and ChargePoint’s Home Flex, have adjustable current settings. These chargers may cost more, but they provide flexibility for future upgrades.
  8.   Schedule charging during off-peak hours: Charging your electric car during off-peak hours can potentially increase charge speeds since there is less demand on the electrical grid.
  9.   Regularly maintain your EV and charger: Ensure your electric vehicle and charging equipment are well-maintained to optimize charging efficiency.
  10. Use the True Energy appWe help optimise your charging and make it easy for you to just create a charge rule – we call it set & forget – and save money – and CO2.