Do electric vehicles need to be charged to 100% every time?

1. Does the battery have to be fully charged?

Electric vehicle lithium batteries have no memory effect and can be charged and discharged at any time without affecting their battery capacity. This is unlike the nickel-metal hydride batteries and nickel-chromium batteries of the early years, which would damage the battery if they were not fully charged. The most important thing to prevent lithium batteries is “overcharging” and “overcharging”, that is, continuing to charge the battery when it is already 100% full, or using up the battery power, which will cause the battery to lose power and damage the battery. 20%-80% is the best working range for lithium batteries.

Electric vehicle charging

2. Lithium battery charging method: voltage-limited constant current method

Below is the lithium battery charging curve. As can be seen from the figure below, it is mainly completed in three steps:

Lithium battery charging curve

  • Step 1: Determine that the voltage is <3V, and pre-charge first, 0.05C current;
  • Step 2: Determine that 3V < voltage <4.2V, constant current charging 0.2C~1C current;
  • Step 3: Determine that the voltage is >4.2V, constant voltage charging, the voltage is 4.20V, and the current decreases as the voltage increases until it is full.

3. The charging time of the car is related to the battery capacity

For refueling, the time difference between filling up and filling up half is not much. But lithium batteries are different. The following figure is a curve of charging current, charging capacity and charging time. It can be seen from the curve that it only takes 1 hour to charge to 80% capacity with a current of 1C, and it takes more than 3 hours to charge to 100%. It must not be overcharged, so the charging time needs to be slowed down when the capacity reaches 80%.

Relationship between lithium battery charging time and capacity

4. Best charging method

In daily use, you can choose the “shallow charge and shallow discharge” method, charging the SOC to 80% to reduce unnecessary charging waiting time.

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