What is one reason your laptop would need a new battery?
If you left it charging all the time, or it's an older battery (a year or two.) Batteries will wear out from normal use.
if it got wet or smacked.maybe you use the battery it oover drains
If you have to charge all the time and it holds almost no charge
You keep the battery in the laptop while you're using it and it's plugged it. Your laptop gets hot. Heat decreases battery life.