EV charging reliability: What charging success rates reveal about public EV charger uptime

As the e-mobility transition continues, uncertainty around EV charging reliability remains an area of concern for current and potential EV drivers. Knowing that reliability is a significant pain point, Kempower has measured charging success rates across its chargers since the first were installed in 2018 using the data on ChargEye, Kempower’s EV charging management software. 

Today, Kempower’s extensive database, which has recorded over 13 million successful charging sessions between 2018 and 2024, reveals insights into the most common causes of EV charger failures. These findings are important for helping EV charger manufacturers, CPOs and EV drivers improve the charging experience. 

This blog post provides an overview of useful charging success rates, why they are important, and what they reveal to us about how we can improve the public charging experience. 

How is EV charging reliability measured?  

The charging success rate (charging SR) indicates the proportion of successful charging attempts out of the total number of sessions taking place at a charge point. It is a useful metric to measure the overall performance and reliability of an EV charging station, providing a clear picture of the end-user experience.  

Success rate metrics can be segmented into more specific categories to pinpoint issues and areas for improvement. Understanding the purpose of each success rate helps CPOs and charger manufacturers identify actionable steps toward improved reliability. 

• The technical success rate (technical SR) monitors unsuccessful charging attempts due to technical issues, caused by either the EV or the charging equipment. Common causes of a technical failure include problems with the plug locking mechanism, EV communication issues or charger issues. 

• The usability success rate (usability SR) focuses on unsuccessful attempts caused by user-related issues. Factors that can negatively influence the usability SR include complicated charging apps, user missteps such as forgetting to connect the plug or authorize the charging session, or deauthorized sessions due to insufficient credits or an invalid authorization tag. 

What do charging success rates reveal about the reliability of public EV charging stations?

Data gathered across 13 million charging sessions show that the majority of technical failures can be attributed to two main causes: EV communication issues, which account for ~47.1% of all technical failures, and locking issues, which make up ~44.1% of all technical failures. EV communications issues typically originate from the vehicle itself and are caused by software bugs. Problems with the plug locking mechanism can originate from a variety of sources such as a faulty EV connector, a worn-out plug, or improper connection by the user. Purely charger related issues, which include failures mainly related to the charging station such as hardware malfunctions, worn-out parts or firmware bugs, only occur in around ~5.0% of instances and other issues occur in 3.4% of all technical failures.  

The leading reason for usability failure is “No Authentication,” accounting for ~75.7% of all usability failures. This error occurs due to user negligence or an overly complex charging app. The second most common usability failure is “Cable Not Connected” at ~13.8% of all usability failures, simply meaning the end-user forgot to plug their EV in. User missteps account for ~9.5 % and deauthorized sessions make up just ~1% of all usability failures.  

The key to improving reliability is to reduce user-oriented failures

When these different EV charger success rates are broken down, findings show that 9 out of 100 charging attempts fail due to user error compared to just 3 out of 100 due to technical errors. To put it another way, user-oriented errors make up 81% of failures, compared to just 19% caused by technical faults.  

The high prevalence of user-oriented errors suggests efforts to optimize the EV charging experience are best focused on improving charger usability. This requires measures by EV charger manufacturers and CPOs to educate EV drivers about how to successfully conduct a charging session, which can come in the form of improved charging apps, site designs and more intuitive charger design. 

In our upcoming blog post, we will delve deeper into the specific actions that CPOs and charger manufacturers can take to improve the reliability of chargers and guide EV drivers toward a seamless experience at the charging station. 

Read more about our findings about charging success rates in public charging in our new white paper. 

Written by

Mikko Veikkolainen

Vice President of Research and Innovation, Kempower