Why Hyundai and Kia EVs slow down when charging on Tesla Superchargers

Why Hyundai and Kia EVs slow down

The main reason why Hyundai and Kia EVs slow down is that the car and charger use different voltage amounts. Hyundai and Kia electric vehicles are designed with an 800-volt battery architecture for rapid charging.

However, the existing Tesla V3 Supercharger network has a maximum voltage output of 500 volts. This difference means the power cannot flow directly into the battery. The car’s internal computer must force a conversion to match the voltages, slowing the process right from the start.

The electric booster limits power to battery

Due to the 500-volt input, the car must utilize its electric drive motor and inverter as a boost converter to step up the power to 800 volts. This extra work generates heat, limiting the amount of power the car can safely accept.

Tests show that a Kia EV6, which can handle 235 kW, often peaks at a significantly lower level, around 126 kW, at a Supercharger. This power cap forces the charge session to take much longer than it would at an 800-volt station.

Conversion process heats up and throttles speed

As the conversion unit works harder, it generates a large amount of heat inside the car’s components. If the temperature becomes too high, the Battery Management System must intervene to prevent damage.

This thermal throttling causes the charging rate to drop sharply. An Ioniq 5 with the larger 77.4 kWh battery pack can take up to 30 minutes to charge from 10% to 80% on a Supercharger, compared to its optimal time of 18 minutes.

Lower Amps further limit older cars

The 500-volt limitation also means the charger cannot deliver the high current, or amps, required by the 800-volt car. The V3 post is rated for up to 615 A.

In many third-party tests, E-GMP cars peak around 120–130 kW on V3, which is materially below the 230 kW they reach on a 350-kW CCS. This lower power means a large car like the Kia EV9 may take up to 40 minutes to charge from 10% to 80%.

High state of charge causes sudden drop

Further into the charge session, drivers see another significant slowdown when the battery reaches about 80% State of Charge. The power can quickly drop to very low rates, sometimes as low as 3 kW.

This drop is a safety feature that requires the Battery Management System to perform cell balancing. Cell balancing ensures the voltage is even across all 32 battery modules in the pack for safe charging up to 100%.

Future V4 Superchargers will solve the issue

V4 introduces higher-power hardware (up to 500 kW cabinets) and longer cables, which better accommodate 800-V vehicles. This high voltage perfectly matches the 800-volt requirement of Hyundai and Kia vehicles.

Once these chargers are widely deployed, the cars will charge at their full speeds of over 230 kW, removing the need for the slow on-board booster. The first full U.S. V4 site opened in Redwood City, California, on Sept. 29, 2025.

Other networks offer better charging speeds

In addition to the V4 solution, due to the 500-volt Supercharger limit, drivers should consider other high-speed networks that support 800 volts. Networks like Electrify America and IONITY are built for this.

For example, the Kia EV6 charged at 230 kW at an Electrify America station, which is much faster than the 120 kW cap on a V3 Supercharger. Electrify America was the first to charge an 800-volt car at 270 kW on Sept. 4, 2019.

Industry wide push for 800 volts is common

The problem of 400-volt stations slowing down 800-volt cars affects many brands. Other luxury electric vehicles, such as the Porsche Taycan and Lucid Air, also utilize the 800-volt standard.

This trend is pushing the charging industry to upgrade. By November 2025, the U.S. had over 65,000 public DC fast-charging stalls.

Next-gen Kia models get the correct port

To simplify access, Kia is planning to install the NACS port directly into new models. The new 2026 Kia EV4 will come with the native NACS charging port when it launches in the U.S. market in early 2026.

This gives drivers immediate access to over 16,500 NACS fast chargers. However, since the EV4 is a 400V battery car, it will still experience a slower charge than a dedicated 800V car on older Superchargers.

High-performance models sustain a fast speed

Interestingly, the voltage limitation is less harsh on high-performance models like the Ioniq 5 N. Although its peak power is limited by the V3, its steady charging curve is strong.

The Ioniq 5 was observed to charge at a peak of 123 kW in a Supercharger test, and it maintained a higher charge rate for an extended period. This strong curve allows the Ioniq 5 to gain 59.6 kWh in a 30-minute and 37-second charging session.

Hyundai is adding native ports in late 2024

Following Kia’s lead, Hyundai is also adopting the North American Charging Standard. All new or updated Hyundai electric vehicle models will feature the native NACS charging port, starting in Q4 2024, in the United States.

This will provide new buyers with immediate access to more than 12,000 Superchargers. Owners of older models with the CCS port will be offered a free adapter starting in the first quarter of 2025 for access.

Want to understand whether contact-free charging pads can truly support everyday EV use in the United States? Read more in Is wireless EV charging the future.

Other high-power networks are expanding fast

Finally, beyond Tesla’s V4, other charging companies are rapidly adding high-power stations. New Electrify America stalls, for example, are equipped to deliver up to 400 kW per vehicle, far exceeding the V3 Supercharger’s limit.

This effort is supported by significant investment and is expected to install nearly 16,700 new public fast-charging ports nationwide during 2025. This expansion ensures that 800-volt cars have reliable and fast charging options.

Curious how major store chains are changing their plans for public chargers after studying costs and slow returns in 2025? Learn more in Convenience store chains rethink EV charging investments.

Have you noticed slower charging on shared networks? Share your experience below.

Read More From This Brand:

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This slideshow was made with AI assistance and human editing.