It all depends on what type of battery it is, what it's made of.
But most laptop batteries will lose performance over time, or will not hold a full charge after a year or two, especially if they've been left plugged in to the charger long after they are fully charged. There's usually no way to get them back to "as new" condition when that happens.
Only remedy is to replace the battery with a new one if it's not sealed in to the casing. Then remember to remove the battery whenever you use your laptop direct from a mains socket.