How DC fast charging works

AC vs DC charging

Your home charger and Level 2 chargers provide alternating current (AC). The car's onboard charger converts AC to the DC current that actually goes into the battery. DC fast chargers bypass the onboard charger entirely — they send DC directly to the battery at much higher power. That's why fast chargers are limited by the battery and its thermal management, not the car's small onboard charger.

The charge curve

EV batteries don't charge at constant speed. They charge fast from 5–80% and deliberately slow down from 80–100%. This is the charge curve. At 10% SoC, a Tesla Model 3 accepts 250 kW at a Supercharger V3. At 80% SoC, it might accept 50 kW. The BMS (battery management system) controls this precisely to protect the cells.

Why the car slows down near 80%

Lithium-ion cells can be damaged by overcharging, especially when they're already full. The BMS reduces power input to prevent lithium plating on the anode — a condition that permanently reduces capacity. This is physics, not a manufacturer limitation. Charging from 80–100% takes as long as 10–80% in some vehicles.

What determines your peak charging speed

Peak charging speed is limited by the lowest of: the charger's maximum output, the car's maximum DC acceptance rate, and the current battery temperature. A 350 kW Electrify America charger means nothing if your car accepts only 150 kW. Check your car's spec sheet for 'DC fast charge acceptance' — this is the real number.

• ·Tesla Model Y LR: up to 250 kW (Supercharger V3)
• ·Hyundai Ioniq 6: up to 240 kW (800V architecture)
• ·Ford F-150 Lightning: up to 131 kW (lower acceptance rate)
• ·Kia EV6: up to 240 kW (800V architecture)

Battery preconditioning for fast charging

Cold batteries can't accept full fast-charge speed. Most modern EVs automatically precondition the battery when navigation routing to a fast charger — the battery is warmed to optimal temperature before you arrive. Enable this by routing to the charger in your nav, not just driving to it without nav.

The 20–80 rule for road trips

For road trips, arrive at a fast charger at ~20% and charge to ~80%. That's the bulk of the fast part of the charge curve. Charging from 80–100% at a fast charger wastes time and money at diminishing speed. Arrive with margin, charge to 80%, and move on.