What Happens to an EV Battery When Left Uncharged for Days or Weeks?

Have you ever left your electric vehicle (EV) uncharged for a few days or even weeks? Just like turning off your tablet and putting it in a drawer, an EV operates with a larger battery, but it also has a 12V auxiliary battery. This article will explore what happens to an EV battery when it is left uncharged for an extended period.

Common Concerns and Misconceptions

Many people worry that leaving an EV uncharged for any duration can significantly deplete its main battery, leading to issues such as needing to be towed. However, the reality is significantly less dramatic. For instance, even when an EV is left uncharged, you may not observe substantial battery loss, especially if the car remains powered by its 12V battery for certain functionalities.

Impact of Left-Uncharged EV

So, what actually happens if you let an electric vehicle sit with no charge for a few days? In reality, if the car is left unused and the main battery is not connected, the onboard 12V battery will power essential components without significant depleting the main battery. However, certain features may still require power, such as the sound system, lights, and wipers. This is why many EVs, like the Hyundai Kona, will prompt you to turn the vehicle on to operate these functionalities. But generally, the main battery will not fully discharge under normal circumstances.

Real-Life Examples and Observations

Real-life examples verify that an EV can indeed lose some range when left uncharged for extended periods. For instance, the author left their Model Y in the garage at the airport for two weeks and found that the state of charge had dropped by around 3%. Even though the temperature was in the low 60s and the car had been in the shade, with no other accessories, the battery still experienced some discharge.

The rate of battery discharge under these conditions is approximately 2% per week. Therefore, if the car is charged to 100% frequency, the battery will eventually run out in about a year. This makes regular charging even when the EV is not in use a critical aspect of EV ownership.

Factors Affecting Battery Discharge

The rate of battery loss can vary based on several factors, such as the car model and specific features that are active even when the vehicle is idle. For example, in vehicles like the Tesla Model 3, the car remains powered by the onboard computer, which can consume battery power. Key features include:

The EV remains on and connected to the internet for various purposes, such as finding the car’s location and remotely controlling functions. Entry to the car recognizes your cell phone through Bluetooth. Sentry mode captures videos, meaning the camera is on while the feature is enabled. The car maintains ambient cabin temperature when not in use, but turns off this feature when the battery power is low.

Even without driving, the onboard computer is active, and this can lead to a small degree of battery discharge. Therefore, while the battery may not completely drain, it is essential to keep it charged to maintain the health and longevity of the battery.

Conclusion

The conclusion is that while an EV will inevitably lose some charge when left uncharged for days or weeks, the rate and extent of this loss are usually manageable. This is true for both EVs and internal combustion vehicles (ICVs), which also rely on the 12V battery for various components. However, it is crucial to keep your EV’s battery charged to ensure optimal performance and battery health over the long term.

Despite these concerns, if you do need to leave your EV at an airport garage for an extended period, it is wise to arrange for alternative transportation to avoid the costs of long-term parking fees. Some EV manufacturers, like Tesla, recommend always plugging in the charger even when it is not necessary, aiding in maintaining the battery’s charge level.