Dim the screen as much as you can tolerate, and lower the CPU speed as much as possible.  Shut off as many running services you don't need as possible. However, this is an extreme budget system - you're not going to get long battery runs out of it;  the goal in designing it was to make it as inexpensive as possible.  Every other consideration came after that.  
My new laptop dell vostro 3510 lasts battery only 3.30 hrs kindly please help me how to resolve it
Battery lasts only 3.30 hrs