Should I charge my EV to 100%?

Electric vehicle (EV) driving range has expanded significantly in recent years. According to data from the U.S. Department of Energy, the average EV range more than doubled from 2017 to 2021, from 114 miles to 234 miles. Some newer models can go more than 400 miles on a single charge.

 

Despite these advancements, many cautious drivers cite range anxiety as their top reason to delay switching to a fully electric car. Underneath that concern may be a deeper worry: What if 234 miles isn’t really 234 miles? After all, there’s a commonly cited rule that you shouldn’t charge your EV past 80% or you risk damaging the battery. In that case, some may reason, 234 miles is actually just 188 miles.

 

Is that rule true, or just a myth? You may be wondering, “Should I charge my EV to 100%?” Or will doing so significantly affect its performance and shorten its life? We’ll explore those questions and offer some tips for preserving your EV battery below.

 

The 80% rule for EV batteries

So, is the 80% rule for EV batteries legitimate? Yes and no. On one hand, it’s better for your battery’s performance and longevity if you keep its charge between 20% and 80% of its capacity. This is known as the 80/20 rule, and that’s considered the optimal performance range for the lithium-ion batteries that power electric cars.

 

Within that range, the car offers its most fuel-efficient performance. Besides that, you also save battery life. Consistently charging your battery to full capacity and discharging it to near zero may accelerate degradation of the battery materials designed to hold a charge and transmit energy. Studies have shown that consistently operating an EV outside that 80/20 window accelerates the conductivity loss that would otherwise naturally occur over a longer period.

 

However, it’s important to note that battery degradation occurs gradually. An occasional full charge or dip below 20% will not irreparably damage your battery or significantly damage its performance. The 80/20 rule is more of a guide for everyday best practices when driving an EV—it’s best to keep your charge within this range, but it’s not a big deal to charge your EV to 100% from time to time. The good news is that even 60% of the average EV battery range of 234 miles still leaves 140 miles—more than enough for a typical daily commute.

 

Besides being a good rule of thumb for battery health, the 80/20 rule also applies to public charging etiquette. Since it takes much longer to charge from 80% to 100% than it does to charge from 0% to 80%, it’s best to move on and free up the charging station for someone else when you’ve reached the 80% mark. This will also save you money, as public fast charging is usually more expensive than charging at home.

 

Fast vs. slow charging and EV battery performance

Although it gets less attention than charging limits, charging type is also an important consideration for long-term battery health. There’s some evidence that frequently relying on DC fast chargers (DCFC) can cause battery degradation. However, the effect of fast charging may not be quite as clear-cut as studies imply. For instance, the available data rarely accounts for any differences between drivers who charge to 80% and those who charge fully when using DCFC.

 

Vehicle make and model can also make a significant difference. An Idaho National Laboratories study of several 2012 Nissan Leaf models showed a statistically significant difference between the battery capacity of cars that relied on DCFC and those that used Level 2 chargers. In contrast, a Recurrent study of more than 12,500 Teslas showed no significant difference in the battery health of Teslas that frequently relied on fast charging and those that only used it rarely.

 

Newer EV models have more robust systems in place to support battery health. Software to control charging time and speed, along with hardware to maintain ideal battery temperature during charging, can mitigate the damage caused by fast charging and extend battery capacity.

 

Other factors that can affect EV battery life

Charging limits and type may be the biggest factors people know of when it comes to EV battery longevity, but a few other variables may have an impact.

 

Extreme temperatures

While the effects of hot and cold temperatures on general battery performance are well documented, many drivers may be unaware that these variables can also impact longevity.

 

For instance, predictive modeling by the National Renewable Energy Laboratory estimates that today’s EV batteries will last between 12 to 15 years in moderate climates but only eight to 12 years in extreme climates. Vehicles with better thermal management systems may be able to offset this difference, but other cars require more attention to charging temperature to prevent faster degradation.

 

Frequently leaving too little charge

Maintaining sufficient charge in your battery can help protect the battery. This is the other side of the 80/20 rule: Avoid discharging the battery fully, as it relies on maintaining a charge to preserve battery capacity. Most manufacturers design their batteries so they will never fully discharge, but it’s still best to avoid coming close.

 

How often should I charge my EV to 100%

When it comes to charging your EV, it’s smart to exercise some caution so you can preserve your battery. Avoid frequent fast charging or charging when the battery is especially hot or cold. Relying on Level 2 chargers at home or at work and supplementing Level 3 fast charging only when needed can help to preserve battery life and performance, especially if you drive an older EV with less robust battery temperature management.

 

In general, though, the 80/20 rule is the best guideline for preserving long-term battery health. Keeping your battery level between 20% and 80% full most of the time will go a long way toward preventing degradation.

 

Use smart chargers like Enel X Way’s JuiceBox^® to manage your charging. Set charging limits to automatically stop at 80%, schedule charging time, or limit the process to times when energy is cleaner and cheaper. Whatever your needs, charging with JuiceBox gives you complete control.