Why are we only supposed to charge EV batteries to 80%?

Charging an electric vehicle battery only between 20% and 80% is often recommended, and the article says the rationale comes down to time and money. It argues that lithium-ion batteries are typically most efficient to charge within that band, especially on DC fast chargers, where speed tends to fall sharply after 80%. The piece also describes battery stress as a factor, noting that charging to 100% can increase chemical strain and prolonged heat exposure, while charging to very low levels can stress internal systems. It says charging to 100% can be appropriate for trips, and mentions automakers such as Volvo and Polestar recommending up to 90%. It also points to different behavior with LFP chemistry.