You may be able to set the system up to improve that a bit (make sure the screen is as dim as you can tolerate, the CPU is set to slow speed, etc.)., but 3-4 hours is about what you can expect from a budget system like this with a relatively small, 3-cell battery. There is an option for  a 4-cell battery (which will fit only if you do not have a 2.5" drive), but that does not appear on any of the current configurations.  That battery should extend runtime by about 25%.  
I bought the laptop yesterday and one time charge stays only for 3 hours
My battery drains fast