My laptop run out the battery power very quick?

Question: HP DP399A battery gives me a note that remaing time is 3 hours and after 5 minutes it's gives me another note saying that remaing time is three minutes change you battery or turn off you computer. I thought that my battrey is dead that's why I change it with a new one and i'm still have the same problem. Answer:Try changing the power settings of your laptop to conserve battery life when idling. You can do this in the "Control Panel."But you'd better buy new one .ASUS A2 battery , ASUS A2000 battery , ASUS A3 battery , ASUS A3000 battery , ASUS A4000 battery , ASUS A8 battery , ASUS A9 battery , ASUS F8 battery , ASUS M2 battery , ASUS M2000 battery , ASUS M2400 battery.hope you solve you question as soon as possible.