When you plug into a DC Fast EV Charger, you might expect a constant, blazing-fast speed from 1% to 100%. In reality, the charging rate follows a dynamic "charging curve," a carefully managed profile that optimizes for both speed and battery health. Understanding this curve helps set accurate expectations for your charging stop.

Phase 1: The Ramp-Up
At the beginning of a session, when the battery state of charge (SOC) is very low (e.g., 10-20%), the DC Fast EV Charger and the vehicle's BMS will quickly ramp up the power to the vehicle's maximum acceptance rate. This phase is brief, as the goal is to reach peak charging speed as soon as safely possible.

Phase 2: The Plateau of Peak Power
This is the golden period of fast charging. Once the battery is conditioned and within its ideal voltage range, the DC Fast EV Charger will deliver sustained peak power. For a vehicle rated at 150 kW, this might mean holding at or near 150 kW from roughly 20% SOC up to 50-60% SOC. This is where you gain the most miles per minute.

Phase 3: The Taper
As the battery fills, its internal resistance increases and the risk of overvoltage rises. To protect the battery, the BMS instructs the DC Fast EV Charger to gradually reduce power. This taper usually begins around 50-80% SOC, depending on the vehicle. You'll notice the charging speed on the display start to drop steadily. By the time you reach 80%, the power may have decreased significantly.

Phase 4: The Slow Finish
Above 80-90%, charging slows to a pace similar to Level 2 AC charging. The final few percentage points take a surprisingly long time because the DC Fast EV Charger is now delicately balancing the cells at a full state. This is why it's almost always inefficient to charge to 100% at a DC Fast EV Charger unless absolutely necessary for your journey.

Factors Influencing Your Curve

Battery Temperature: A cold battery will charge slowly until it warms up. Many EVs have a "preconditioning" feature that heats the battery when you navigate to a DC Fast EV Charger.

Station Power: Your curve is capped by the station's maximum output. A 50 kW charger creates a low, flat curve compared to a 150 kW unit.

Battery Health and Chemistry: Over time, a battery's ability to accept peak power may gently decrease. Different battery chemistries also have different ideal curves.

The key takeaway is that the optimal use of a DC Fast EV Charger is to charge from a low state (10-20%) up to 80%. This targets the steepest part of the curve, giving you the most range in the shortest time and preserving your battery's long-term health.