Understanding the Battery Charging Curve in Electric Vehicles

Understanding the Battery Charging Curve in Electric Vehicles

As electric vehicles (EVs) are becoming more popular, it’s important to understand some of their key aspects. Whether you’re planning to buy an EV or already own one, learning about the technology can help you make better decisions. One crucial concept is the “EV Battery Charging Curve.” Let’s explore what it is, how it works, and why it matters for the efficiency and longevity of your EV’s battery.

What is an EV Battery Charging Curve?

In simple terms, the charging curve is a graph that shows how your EV’s battery charges during a session. It tracks the relationship between the battery’s state of charge (SoC) and the speed of charging. This graph gives you a real-time picture of how energy flows into the battery and how efficiently it’s being charged.

Charging curves are not always linear because they depend on factors like the charging power and battery capacity.

How Does the Charging Curve Work?

The charging process happens in three phases:

1. Rapid Charging Phase:
   Think about filling an empty glass with water from a tap. At first, you’ll pour quickly to fill the glass. Similarly, when your EV’s battery is low (SoC between 0–20%), charging happens at its fastest speed. During this phase, the charger works at full capacity without overheating.
2. Tapering Phase:
   Now imagine the glass is about 70% full. You might reduce the flow to avoid spilling. In the same way, when the battery reaches around 70–80% SoC, the charging slows down. The battery resists taking energy at full speed to prevent overheating. For this reason, it’s often recommended to stop at 80% when using public chargers, as charging beyond that takes much longer.
3. Trickle Charging Phase:
   Finally, when the glass is almost full, you slow the flow to avoid spilling over the brim. Similarly, when the battery reaches near full capacity, the charging slows to its lowest speed. This ensures the battery charges safely to 100% without harming its long-term health. Charging to 100% is best done at home, where AC chargers deliver power slowly and steadily.

Image Source: Zeon Charging

Factors Influencing the Charging Curve

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Several things affect the charging curve:

• Charging Station Power Rating: Fast DC chargers (e.g., 30 or 60 kW) charge quicker than AC home chargers, leading to a steeper curve initially.
• Temperature: Batteries work best within a specific temperature range. Extreme heat or cold can flatten the curve, slowing down charging.
• State of Charge: As the battery gets closer to full charge, the curve flattens, and charging speeds drop.

Why is the Charging Curve Important?

Understanding the charging curve can make life easier for EV owners:

• Optimized Charging Times: Knowing that the first phase charges quickly while the last one takes much longer can help you plan charging sessions better. For daily use, charging up to 80% may save you time. Read more on why charging 80% is deal at public charging stations.
• Battery Longevity: Pushing your battery to 100% regularly, especially using fast chargers, can wear it down. By following the curve, you can adopt habits that keep your battery healthy, like partial charges.
• Energy Efficiency: Faster charging may result in energy loss due to heat. Recognizing this can help you choose more efficient charging options.

Know the difference between battery capacity and charging speed

Conclusion

The battery charging curve is more than just a technical concept—it’s a practical guide to making the most of your EV. By understanding how it works and what affects it, you can save time, extend your battery’s life, and improve efficiency. Whether you’re a seasoned EV owner or a curious newcomer, mastering the charging curve will elevate your experience and help you get the most out of your vehicle.