The idea of overcharging a battery is to leave your electric car plugged in with the battery pack at 100% charge while still pumping electrons into it. This might cause overheating and ultimately damage. Battery fires would be the worst scenario.
But, manufacturers of electric vehicles have built safeguards into their software to guard against overcharging, deep discharging, and overheating. By reducing the charging rate as the battery approaches 100% and eventually stopping charging, the battery management system safeguards the battery from overcharging. preventing the overcharging of electric vehicles.