What CPOs Look for in an EV Charger: Insights from 160+ Model Benchmarks

Most conversations about EV chargers focus on equipment cost, installation complexity, and required power capacity. Those matter, but they are not what determines whether a charger survives real-world network traffic, peak-hour loads, roaming sessions, and firmware cycles.  

After working with more than 160 models across multiple manufacturers and regions, I have seen the same pattern repeat. CPOs value hardware that behaves predictably under various situations. They look for stability in OCPP communication, consistent uptime, clean firmware logic, and strong error recovery. This is what separates network-ready chargers from devices that only perform well in isolated testing. 

In this article, I will explain what the data shows. My goal is to give hardware manufacturers a reference point for how CPOs evaluate the chargers they deploy. Every point comes from real-world certification work, live networks, and thousands of active charging sessions. 

Why benchmarks matter 

Benchmarks reveal how a charger behaves across hundreds of sessions and dozens of edge cases. They expose timing issues, state machine flaws, and communication gaps that are hard to detect in lab environments. A CPO depends on these insights because a charger with poor OCPP behaviour affects the entire network. Problems cascade. Slow transaction start sequences create queues. Incomplete session records break billing logic. Weak error handling leads to increased downtime. 

When we benchmark a charger model, we evaluate: 

• OCPP communication flow and timing 

• Authentication logic for RFID, app, and roaming 

• Transaction start and stop consistency 

• Firmware stability 

• Over-the-air update behaviour 

• Power delivery accuracy and fallback logic 

• Recovery from real-world failure states 

Each benchmark covers the same baseline scenarios. This makes results comparable across manufacturers and charger categories. 

2. The four categories that CPOs care about most 

After reviewing data across more than 160 models, four categories show the highest correlation with long-term reliability. These categories also influence operational costs for CPOs. 

2.1 Uptime under real network conditions 

Uptime has two layers: 

1. Hardware uptime 

2. Network uptime 

A charger can power on without problems but still fail to stay online within the network. The most reliable charger models maintain stable OCPP connections even under challenging network conditions. They keep heartbeats consistent, recover quickly from intermittent connectivity drops, retry messages intelligently, and avoid unnecessary disconnects — ensuring dependable real-time communication regardless of network variability. 

What benchmarks show:

• The best models keep heartbeat timing within a narrow range even when session traffic spikes. 

• Unstable models show jitter or unstable network connection, which causes disconnects and missed status notifications. 

• Many models pass lab tests but degrade in the field example because the wireles network singnals are weaker which itself then can cascade to blocking operations during transactions. 

CPO takeaway: True uptime is the percentage of time the charger remains functional, reachable, and responsive to backend commands. Powering on is not enough. Staying connected is what matters. 

Manufacturer takeaway: Focus on non-blocking I/O routines and consistent heartbeat intervals and keeping the websocket connections alive. Use stress tests to detect timing variance early. 

2.2 OCPP reliability and compliance 

OCPP is the core interface between the charger and the network. Even small inconsistencies create large operational problems. The benchmark data shows that OCPP behaviour varies more across models than any other feature set. 

Patterns from the dataset: 

• Clean state machine transitions correlate strongly with low session failure rates. 

• Chargers that queue messages correctly handle roaming and app payments more reliably. 

• Models with inconsistent error reporting create silent faults that are hard for CPOs to diagnose. 

• Many chargers support OCPP features on paper but implement them partially or with timing gaps. 

Common OCPP failure points:

• StartTransaction timestamp on the charger is wrong, or measurement reading is wrong. 

• StopTransaction missing or incomplete, charger clock not synced and timestamp is wrong or measurement is wrong. 

• Incorrect meter value formatting, not using same logic to read values as in transaction events. 

• Faulted state transitions that never reset 

• Firmware update operations not clearly documented or failing on download 

• Unnecessary use of proprietary extensions 

CPO takeaway: CPOs rely on predictable OCPP behaviour to support payments, energy reporting, smart charging, and remote support. 

Manufacturer takeaway: Use automated OCPP regression testing for every firmware release. Respect timing requirements and state transitions. Avoid proprietary hacks because they create long-term maintenance costs. 

2.3 Session success rate

Session success rate is the most visible metric for drivers and CPO support teams. In the dataset, the most reliable chargers show a clear pattern. Their firmware handles uncertainties gracefully. They treat external conditions such as roaming delays and physical connector issues as part of normal operation instead of exceptional faults. 

What the highest performing chargers have in common:

• They handle slow authentication providers without interrupting the start sequence. 

• They read energy meters at correct intervals and with correct formatting. 

• They monitor connector locks in real time and recover without manual intervention. 

• They handle roaming-specific latency without double-initiating sessions. 

• They always send complete StopTransaction messages even when faults occur mid-session. 

Session failure reasons that show up most often:

• Timeout during authentication 

• Firmware state machine stuck between Available and Preparing, or suspended and charging in loadbalancing scenarios. 

• Incomplete meter values 

• Charging not started even though EV has signaled readiness 

• StopTransaction missing due to communication drop 

• Inconsistent connector lock handling 

CPO takeaway: A session failure often means a support ticket or a driver who stops using that CPO. Session reliability drives customer satisfaction.

Manufacturer takeaway: Focus on end-to-end session flow. Handle delayed responses gracefully. Treat every state transition as a potential failure point that needs recovery logic. 

2.4 Firmware quality and maintainability 

Firmware quality is the most important long-term differentiation factor. Over multiple models, the gap between well-designed firmware and poorly designed firmware grows with every update cycle. 

Benchmarks reveal: 

• Clean firmware uses modular components that handle state, messaging, and error recovery in a predictable way. 

• Poor firmware mixes low level car communication logic with communication logic. This leads to tangled flows and unstable behaviour. 

• Some models regress after updates, which means the firmware does not have strong automated testing. 

• OTA update procedures vary widely. The most mature models complete updates with new firmware validation and automatic rollback booting etc. 

Characteristics of high-quality firmware:

• Stable state machine 

• Non-blocking architecture 

• Predictable error handling 

• Clear separation between logic layers 

• Full OCPP regression tests before release 

• Ability to roll back safely 

CPO takeaway: Firmware quality determines whether a charger becomes more reliable or less reliable with each update.

Manufacturer takeaway: Invest in architecture early. Build a regression test suite for OCPP and session flows. Treat OTA updates as a core part of the product, not an afterthought. 

3. What the dataset shows about maturity across charger manufacturers 

Across more than one hundred sixty models, a few patterns stand out. 

3.1 Newer manufacturers often ship with basic OCPP issues 

Younger hardware companies usually move quickly through prototyping phases. They may focus on hardware design first and postpone software maturity. Benchmarks show common issues such as:

• Overly complex state machines that are hard to maintain 

• Timing problems during Transaction messages or Meter Values 

• Incorrect handling of connector faults 

• Large firmware images that slow down OTA updates 

These issues are solvable, but they create operational risk for CPOs. 

3.2 Mature manufacturers behave more consistently but still produce outliers 

Large and established manufacturers usually have strong OCPP and firmware teams. Their models show more predictable behaviour across scenarios. Still, they sometimes introduce regressions after major firmware changes. This highlights the need for automated testing across all models. 

3.3 The strongest manufacturers work closely with their CPO partners 

The most reliable models come from manufacturers who run continuous integration with real backend systems. They treat backend partners as part of their test environment. They run controlled stress tests before release and use benchmark data to adjust firmware. These manufacturers improve with each generation of hardware. 

4. The metrics CPOs use when selecting chargers 

CPOs evaluate chargers using metrics that help predict long-term performance. These metrics guide procurement and deployment decisions. 

4.1 Transaction success rate 

Percentage of sessions that complete with correct start and stop data. This is the most important indicator of how well a charger behaves in real networks. 

4.2 OCPP timing stability 

Consistency of message timing across hundreds of transactions. Timing variance is a strong predictor of future communication faults. 

4.3 Heartbeat reliability 

Percentage of heartbeats delivered within the expected interval. Deviations indicate firmware blocking issues or network instability. 

4.4 Firmware update stability 

How reliably a charger completes OTA updates without corruption or disconnection after the update. 

4.5 Error recovery behaviour 

How quickly a charger returns to Available state after: 

• EV communication errors 

• Connector lock events 

• Network drops 

• Meter value issues 

4.6 Data completeness 

Whether meter values, phases, temperature readings, and session records are complete and correctly formatted. 

These metrics give CPOs confidence when scaling their networks. They know what to expect from the hardware and how to plan support resources. 

5. What manufacturers should implement before talking to CPOs 

Based on the benchmark data, manufacturers can follow a clear checklist to prepare chargers for network environments. 

Required capabilities: 

1. Clean and predictable state machine 

2. Full support for OCPP core message flows 

3. Graceful handling of delayed responses or multiple simultaneous incoming messages 

4. Consistent meter value formatting 

5. Reliable connector lock monitoring 

6. OTA updates that complete without interruption 

7. Automated OCPP regression tests 

8. Session recovery logic for communication drops 

Design recommendations:

• Keep firmware modular. 

• Use non-blocking communication flows. 

• Validate all energy reporting formats. 

• Test every firmware release with a backend. 

• Avoid proprietary extensions unless absolutely needed. 

• Run stress tests with hundreds of back-to-back sessions. 

• Validate session logs with roaming providers. 

These improvements reduce integration time and help CPOs launch networks faster. 

6. How to use benchmark data to improve charger design 

Benchmark data helps manufacturers track progress and find issues that lab tests rarely uncover. 

6.1 Compare versions 

Use benchmark reports to compare firmware releases. Track regressions in timing, session success, and error handling. 

6.2 Prioritize fixes based on CPO impact 

Solve issues that affect session success first. Then solve issues related to uptime. After that, optimize performance or add new features.

6.3 Use session timelines 

Detailed session logs show exactly where delays and faults occur. These logs help engineers locate and fix state machine problems. 

6.4 Review OTA update behavior 

A single OTA issue can take a charger offline for hours. Benchmarks reveal the reliability of the update process. 

6.5 Track long-tail errors 

Many models have rare but serious faults that only appear under heavy load. Benchmark data helps catch these patterns early. 

7. Final thoughts for manufacturers 

CPOs trust chargers that behave predictably across millions of real sessions. After benchmarking more than 160 models, the pattern is clear. Reliability depends on stable firmware, clean OCPP flows, consistent session handling, and strong recovery logic. These elements decide how well a charger performs inside the lab and outside a live network with real users. 

If you build chargers and want to understand how your hardware behaves under real operational load, the eMabler Charger Certification Program gives you that clarity. It evaluates how well a model performs across the full charging journey and verifies that it delivers stable, repeatable, session level results. If you want to learn how your charger performs in these conditions, take a look at the Certification.