First its important to understand what overcharging is:
Over-charging occurs when the charger keeps the battery at a temperature that is warm to touch (body temperature) while in ready condition.
Li-Ion laptop batteries have built-in controller chips which prevent it from overcharging, as they can explode if overcharged. Overcharging does not affect the life span other than potentially destroying the battery.
A lithium-based battery should never be allowed to get warm in a charger. If you have this happen, the battery is no good or the charger is not working properly. Dont continue to use the battery or charger if this happens.
A Lithium-ion battery may be damaged by extensive overcharging (continuously on a charger for more than 24 hours). Damage to the battery from overcharging would only occur in the very unlikely event of a malfunction of the charging system.