Why should not fully charge electric car battery?

The majority of batteries in electric vehicles today are lithium-ion, which is also the type of battery commonly used in electronic devices. For devices using this type of battery, experts always recommend applying the 80-20 rule to keep the battery durable and at its best performance, which means that the battery should not be charged above 80%, or let the battery drop below 20% capacity. There are two main reasons for this: charging efficiency and battery life.

When charging an electric vehicle, whether using a household power outlet or a fast charging station, the charging capacity will decrease significantly when the battery is about 80% full. Above this battery capacity, the charging will switch to trickle charging to avoid overheating the battery, which will affect the battery life. Therefore, the charging time from 20% to 80% can be faster than from 80% to 100%, which can affect the route and travel plan if the owner uses a public charging station to fully charge the vehicle.

In addition, letting the battery drop below 20% capacity can reduce the durability of the battery cells inside, affecting the ability to store electricity if this condition persists and occurs continuously. That is why most electric vehicles today recommend always keeping the vehicle at 20%-80% charge if using the vehicle for daily purposes, running in the city or going on short trips.

Only charge the battery to 100% when absolutely necessary, such as on long trips with few charging stations on the road. When fully charged to 100%, the owner should use the vehicle immediately, not leave the vehicle in a fully charged state without driving for too long. If the vehicle is not used for a long time, the battery should be kept at 80% or lower.

In addition, drivers should note that on some electric vehicles, when the battery is 100% full, the regenerative braking system may not work, or work in a limited way. The Tesla Model 3 owner's manual clearly states that the regenerative braking system will be limited depending on the condition of the battery, when the battery is "cold" (not reaching the optimal operating temperature) or when the battery is full, so drivers need to pay attention to this, in order to proactively brake the vehicle if necessary. Similar recommendations are also available on other electric vehicle models.

However, full charging may not be applicable to some electric vehicle models. For example, vehicles using LFP technology batteries can be charged to 100% without affecting their lifespan or capacity. Charging and maintenance of the battery are clearly stated in the user manual of each vehicle model.