Should you replace laptop battery

Question: How often should you replace battery and are there any signs that you should replace it? Answer:Well, there no exact date or a certain number to change a laptop battery. Most people I know just change it when they feel the hp F4812A battery can hold much power anymore, usually when the battery (new) lasts for 4 hours to 2.5-2 hours. Just change it as you see fit, if your laptop runs out of power alot or how long it can hold a charge goes under like half then change it. But some batteries for laptop cost quite a bit. My replacement for a sony batterywas around 80 dollars. Probably a little less now...I hope.