Why Charging Your EV To 100% Isn’t Always A Good Thing

Level 3 fast chargers are advertised by EV automakers for their ability to rapidly recharge an EV to around 80% in 30 minutes. But as Kelley Blue Book notes, using a fast charger won’t necessarily result in a rapid charge if the battery is under 20% or over 80% when plugged in. This is a safety feature to protect the battery, and it also encourages drivers to keep their car’s battery within these optimal percentages. Driving Electric says that to keep batteries in top shape, they should not be overcharged. Unlike gas cars, where drivers will usually top up the tanks, that is not recommended in EVs. Fully charging an EV battery can damage it and degrade it. Ideally, drivers should let the battery drop to 20% and then charge it to 80%.

When an EV battery is charged to 100%, it heats up. A study published in Nature explains that temperature has a “significant impact on the performance, safety, and cycle lifetime of lithium-ion batteries.” Temperatures affect the Solid Electrolyte Interphase (SEI), not to be confused with the lithium plating. SEI lets lithium ions pass through but protects the anode from corrosion. When the SEI is modified, the protective characteristics are loosened up, and normal chemical reactions are affected. Temperatures can also cause stress fractures and fissures, as Recurrent explains. Fissures and cracks can also cause unwanted chemical reactions and take up a part of the normal flow of energy, eventually degrading the battery.