Why is my battery doesnt last more than two hours?

Batteries have a life that depends on several factors, how old it is, how often the battery cycles between charged and discharged. The best information is to go into diagnostics on your computer, begin with the computer turned off, turn it on and wait for the Dell splash screen to show up and then press F10 and select diagnostics. Run the battery test and it will give you the battery health. Also, check the ac adapter to make sure that the wattage detected by the computer matches the adapter. If the battery health shows good, then look at what apps are running and using up the battery life, if the battery health shows going bad then replace the battery.