Many electric vehicle owners encounter a situation that feels counterintuitive and sometimes even frustrating: two EVs plug into the same public fast charger at nearly identical battery levels, during similar weather conditions, and under seemingly equal circumstances, yet one vehicle charges significantly faster than the other. It is natural for drivers to assume that the slower vehicle is experiencing a technical issue, or that the station is malfunctioning, or that the charger “prefers” one brand over another. However, the reality is that fast-charging performance is influenced by a complex combination of design decisions, engineering limitations, environmental factors, and station-level conditions that vary from moment to moment. When these factors are understood clearly, the differences no longer feel mysterious but instead become predictable and logical.

1. Every EV Has a Built-In Maximum Power Acceptance Limit Determined by Its Design

No matter how powerful a public charger is, each electric vehicle is designed with a specific upper limit on how much power it can accept. This limit is determined by the capacity of the battery pack, the strength of the thermal management system, the charging architecture chosen by the manufacturer, and the safety margins needed to protect the battery over many years of use. A vehicle that peaks at 60–80 kW will never reach the same charging speeds as a model capable of accepting 150–250 kW, even if both are using a charger rated for far more than either needs.
This means that the charger’s rating does not determine your speed—the car’s design does, and that alone explains a large portion of the differences drivers observe daily.

2. Public Chargers Rarely Operate at Their Full Advertised Rating for Every Vehicle

The number printed on the charging unit—120 kW, 180 kW, or even 350 kW—represents its theoretical peak capability under ideal conditions. Real-world output depends on a variety of factors including how many stalls share the same power cabinet, whether the site is experiencing heavy usage, whether the internal temperature of the equipment has triggered automatic power reduction, and whether the grid connection is temporarily limited. Many fast-charging stations use shared power distribution, which means that two vehicles pulling energy at the same time may not receive equal power.
In practice, this means that even two identical cars may see different speeds if one connects during peak load while the other plugs in at a quieter time.

3. Charging Curves Create Natural Variations in Speed at Different Battery Levels

Fast charging does not proceed at a constant rate. Instead, every EV follows a charging curve that dictates how much power it can accept at various states of charge (SoC). Some vehicles maintain high charging power well into the 50–60% range, while others begin tapering early to manage heat or preserve battery longevity.
These curves are carefully designed by engineers, and no two models—even from the same manufacturer—share identical behavior. As a result, two EVs starting a session at 35% or 40% may show dramatically different speeds simply because their charging curves diverge at that point.
This is why charging speed comparisons only make sense when vehicles have similar curves, similar temperatures, and the same charger conditions.

4. Battery Temperature Significantly Influences the Ability to Accept High Power

Lithium-ion batteries operate best within a specific temperature range, and charging power is dramatically affected when the pack is too cold or too hot. In cold weather, the internal resistance of the battery rises, which causes the vehicle to limit charging power to prevent damage. Some EVs include aggressive battery preconditioning systems that warm the battery before the session begins, while others apply much gentler heating or none at all, leaving the pack colder at the start. In hot conditions, the vehicle may also reduce charging power to avoid overheating the cells.
Because different models use different thermal management strategies, two vehicles charging side by side on a winter morning can show charging speeds that differ by more than 50%, even when everything else appears equal.

5. Cables, Connectors, and Adapters Introduce Their Own Limitations

Even when the power cabinet can supply high output, the cable and connector connected to your vehicle may not be rated for the same level of power. Older cables, cables with inadequate cooling, or cables shared by multiple users can impose lower limits. When an adapter is used—even one that is fully compatible—it may introduce additional restrictions based on its rated current, internal wiring, or temperature management.
Although these limitations may not be immediately obvious to drivers, they often contribute to real-world charging speeds that fall short of the theoretical ratings printed on the equipment.

6. Vehicle Software Plays a Silent but Critical Role in Deciding Charging Speed

Behind the scenes, every EV uses a sophisticated software system to constantly monitor battery voltage, temperature, cell balance, resistance, and overall stability. These systems make rapid real-time decisions about how much power to accept from the charger. Some manufacturers favor long-term battery preservation and therefore reduce charging power more aggressively in response to heat or imbalance, while others allow higher peaks when conditions permit.
These invisible differences in software philosophy explain why two vehicles that appear identical in terms of hardware and conditions may still charge at noticeably different rates.

7. External Conditions and Recent Driving Behavior Also Affect Charging Performance

Charging does not occur in isolation from the rest of the driving experience. The temperature of the battery upon arrival is influenced by driving speed, driving distance, recent acceleration patterns, and whether the vehicle has had time to cool down or warm up. A vehicle that has just completed a long highway drive may arrive with a warm, optimal battery, while one that has been parked for several hours may begin charging with a cold battery.
As a result, even two vehicles of the same model can charge differently simply because they arrived at the charger under different circumstances.

Conclusion: Differences in Charging Speeds Are Normal, Predictable, and Not Signs of Failure

When two electric vehicles show different charging speeds on the same public charger, the explanation is almost always rooted in normal engineering differences rather than equipment failure. Variations in maximum power capability, charging curve design, battery temperature, station power distribution, real-time thermal conditions, adapter limitations, and vehicle software all interact to determine the final speed displayed on the screen.
By understanding these factors, EV drivers can better anticipate real-world charging performance, reduce frustration, and make more informed decisions during long trips or daily charging routines. Charging speed is not a simple number; it is the result of many hidden variables working together, and recognizing this helps drivers develop a more practical and confident approach to using fast-charging infrastructure.