Electric vehicle technology has made great strides, and so has the method of charging them. DC fast charging has become a popular option because direct current enables faster and safer charging than using a standard three-prong plug. However, the convenience of fast charging—which reduces waiting time—raises questions about whether the increased battery temperature during charging shortens the battery's lifespan.
Slow charging refers to charging points with power output between 7kW and 22kW, commonly found in residences, which supply alternating current (AC). Since electric vehicle batteries store energy only as direct current (DC), AC charging requires conversion inside the vehicle. This conversion causes AC slow charging to take longer than DC fast charging. Slow AC charging at home helps maintain long-term battery performance because it generates less heat and stress. Fast charging is necessary when in a hurry or traveling long distances. The best practice is a balanced charging approach—prioritizing slow charging at home and limiting fast charging—while avoiding full 100% charges to preserve battery capacity.
Avoiding frequent DC fast charging, vehicles such as sedans and electric vans that use fast charging for less than one-eighth of all charges show a battery performance decline of about 1.5 percent per year.
In contrast, groups using fast charging more frequently experience an average battery performance decline of 2.2 percent per year. For DC fast charging below 100 kilowatts and those using 100 kilowatts or more, data shows battery performance declines by approximately 3.0 percent per year.
Why is slow AC charging better despite taking longer?
Lower battery heat: The lower energy level or current flow generates less heat, reducing wear and tear on the battery's internal components.
Stable lithium-ion chemistry: It helps maintain lithium battery stability, preserving charge capacity and extending battery lifespan.
Charging with AC at home reduces battery degradation. Electric vehicles frequently using DC fast charging (especially above 100kW) degrade faster—about 3% annually—compared to those using slow charging, which degrade around 1.5% per year.
When is fast charging necessary (and how to minimize its impact):
Convenience: It is essential for long-distance travel and quick recharging.
Modern safeguards: Electric vehicles include battery management systems (BMS) that often limit fast charging to 80% capacity to prevent overheating.
Best practices: Use fast charging only when necessary, avoid making DC fast charging a daily routine, and keep charging levels between 20-80%.