Should I charge my EV to 80%, 90%, or 100%?

In a study from 2020, researchers found that the optimal charge level for electric vehicle (EV) batteries is between 20% and 80%. Charging to 100% or letting the battery go below 20% regularly can accelerate battery degradation, so it is best to avoid doing this unless necessary.

However, there are times when it may be necessary to charge to 100% or let it discharge below 20%, for example, if you’re going on a long road trip. 

Advantages and disadvantages of each charge level

Here is a breakdown of the pros and cons of charging your EV to 80%, 90%, or 100%:

Which charge level is right for you?

It depends on your personal driving habits and needs. If you have a short commute and can plug in at home every night, it is best to keep your battery between 20% and 80% charge. Longer commutes or regular long-distance travel may necessitate more frequent 100% charges.

Here are some real-life scenarios to help you decide which charge level is right for you:

• Scenario 1: You are a daily commuter with a 20-mile round trip. You can easily get by with charging your EV to 80% every night. This will give you enough range for your commute and still leave you with some reserve power for unexpected trips.
• Scenario 2: You are a sales representative who drives 200 miles a day. You will need to charge your EV to 100% every night to ensure that you have enough range for your work day. However, you may want to consider using a slower charger whenever possible to help extend the lifespan of your battery.
• Scenario 3: You are planning a 500-mile road trip. You will need to charge your EV to 100% before you leave and then stop to charge at least once along the way. You may want to consider using a fast charger to minimize the time you spend charging.
• Scenario 4: You have solar panels at home and you live in a sunny climate. You may be able to get by with charging your EV to 80% or even 90%. This will give you enough range for your daily driving and still leave you with some reserve power for unexpected trips. You can also use your solar panels to top up your battery throughout the day.
• Scenario 5: You have an older EV and you live in a cold climate. You will want to be more careful about charging your EV to 100%. Try to keep your battery between 50% and 80% whenever possible. This will help to extend the lifespan of your battery.

If you are unsure of which charge level is right for you, consult your owner’s manual or contact the manufacturer.

EV battery degradation

Electric vehicle batteries degrade over time and with use. This degradation affects:

• Battery capacity: How much energy the battery can store, which reduces the range of your vehicle.
• Battery performance: How much power the battery can provide, which reduces the maximum acceleration of the EV and the maximum charging power.

According to a Ph.D. thesis from the Technical University of Munich, battery degradation can be divided into two causes: cycle aging and calendar aging.

• Cycle aging is the loss of battery capacity due to use. The term “cycle” refers to fully charging and discharging a battery. Charging from 30% to 80% and then using your EV until you are back at 30% would be half a full charging cycle.
• Calendar aging is the loss of battery performance over time, even when the battery is not in use. Calendar aging depends on time, but it is accelerated by temperature and the battery’s state of charge. Batteries age faster when they are kept at high or very low charging levels.

For EV users, this means that you should avoid letting your car sit for a long time at a high charging level (such as 90% or 100%) or a very low charging level (such as 10%).

Factors Contributing to EV Battery Degradation

There are several factors that can accelerate EV battery degradation, including:

• Frequent fast charging: Fast charging is convenient, but it can put stress on the battery and shorten its lifespan.
• Extreme temperatures: Both hot and cold temperatures can damage the battery.
• High mileage: Just like a traditional car, an electric car’s battery will wear down over time as the car is driven.
• Age: As an EV battery gets older, it will naturally degrade.
• State of Charge: Keeping the battery frequently under 20% or above 80% leads to a decrease in the battery capacity.

Tips to extend the life of your EV battery

To increase your EV battery lifespan, follow our recommendations below:

• Avoid full charging and deep discharging. 
• Consider the climate. Extreme temperatures can accelerate battery degradation. If you live in a hot or cold climate, it is best to keep your battery between 50% and 80% charge whenever possible.
• Minimize fast charging. Fast charging is convenient, but it can also put stress on the battery. If possible, use a slow charger whenever possible.
• Drive at a moderate speed. Driving at high speeds can drain the battery more quickly.
• If you have solar panels at home, you may not need to charge your EV fully. You can keep some storage left in case you produce your own energy and use it to charge your car later.
• If you have a home charging station, set it to charge your EV to 80% maximum overnight.
• If you know you won’t be using your EV for a while, charge it to 40-50%.
• Avoid leaving your EV plugged in all the time. Unplug it once it is fully charged.

By following these tips, you can help extend the life of your EV battery and save money in the long run.

Conclusion

We’ve interviewed many EV drivers, and most of them said that it took them some time to adjust their habits after transitioning to an electric vehicle. EVs don’t behave the same as combustion engines, so it’s important to understand your personal needs when deciding how much to charge your car.

We advise charging your EV at a moderate speed at home and keeping its battery level between 20% and 80%.