Measuring uptime and reliability for fleet EV chargers

Sashko Stubailo

February 27, 2024
February 27, 2024

EV drivers everywhere have had the same experience – you pull up to a charger you found on an app, and you can't get a charge. Maybe the charger is off, the cable is broken, it doesn't accept your payment, or your vehicle doesn't get enough power.

Uptime and reliability of EV chargers is an important topic of conversation right now, and rightfully so. For fleets, the issue is especially critical – if you can't charge up your rideshare vehicle, delivery van, or drayage truck, you can't run your business at all.

In this article, we'll go over one way uptime is measured today, how charger reliability needs are different for fleets, and how a single uptime metric doesn't capture a variety of common error scenarios.

Existing efforts to measure uptime: NEVI as an example 

NEVI, a program aimed at expanding charger coverage across all 50 states in the US, includes one of the most prominent examples of measuring charger uptime. Let's look at it as an example:

  • 97% uptime. Each charging port must have an average annual uptime of greater than 97%, which allows for about 11 days of downtime per year. There's a minimum required power level of 150 kW for DC chargers and 6 kW for AC chargers.
  • Excluded downtime. Electric utility service interruptions, failure due to the fault of the vehicle, scheduled maintenance, vandalism, and natural disasters don't count as downtime.
  • Outage reporting. Charging stations must have a way to report outages and malfunctions.

All of the details can be found in the code of federal regulations here.

Fleets have even higher charger uptime requirements

The NEVI requirements above are a good starting point, but aren't strict enough for many fleets:

  • Vehicle compatibility is critical. If a vehicle is unexpectedly incompatible with a certain charger, that's just as bad as the charger being down.
  • Maintenance is still downtime. If a charger is being maintained, that still means the fleet can't use it to charge, and could result in lost business for the fleet.
  • 97% may not be good enough. 11 days of downtime is still a lot for critical operations.

However, unlike public charger operators, fleets can take advantage of the more options to improve reliability:

  • Offline chargers can still charge. When a public charger is disconnected from the internet, it often can't charge. However, fleet chargers can be configured to start charging without a network connection.
  • Vehicle compatibility testing. Fleets can test vehicle compatibility and identify issues up front.
  • Driver issue reporting can be extra helpful. Drivers of fleet vehicles might be extra motivated to report charger issues and downtime.

Beyond this, the very idea of measuring uptime as a single percentage metric has some flaws.

Uptime as a metric doesn't cover the most common fleet issues

In our experience with charger management for large charging sites, we've found that charger uptime and connectivity is usually not representative of charger health. It's very common that a charger reports that everything is OK, but there's a one-off issue that doesn't allow charging to happen, for example:

  • Failure to start charging. Many issues, including a vehicle-to-charger communication failure, can prevent starting a charge.
  • Unexpected charging stop. A power outage, voltage issue, or even an unexpected software update from the manufacturer can cause charging to stop.

These would not show up on a "charger uptime" metric as described above, because the charger is not "down" for any amount of time. It's a single point-in-time failure that significantly disrupts operations, but it's unclear if the charger should be considered "broken".

A better approach: combining uptime, charger utilization, and error count

Since most of the issues that affect fleets can't be captured in a single uptime metric, it's important to always look at several metrics for charger reliability in combination:

  1. Uptime and connectivity
  2. Number of charger errors that led to charging disruptions
  3. Number of driver issue reports
  4. Number of successful charging sessions

Chargers often send error signals over OCPP that indicate conditions like not being able to start charging, unexpectedly ending a charging session, and more. Keeping track of how many issues are coming in, and which chargers are reporting the largest number of issues, is likely the best way for fleets to get a handle on their overall charger reliability.

Improving the reliability of EV charging, both public and private, is one of the biggest ways we can all contribute to the adoption of EVs. I'm excited for Flipturn and our customers to continue collaborating on this important issue!