The specification for your laptop click here gives 1.5 hours battery life. As far as data is concerned, once you have saved it to your hard drive it is safe even if the battery goes flat. Most laptops go into a `sleep` type mode if the battery goes flat whilst you are using it and wont run again until you connect your mains charger; this is designed to save any data you are working on.
You should read the manual; it is usually installed on the hard drive and has an icon on the desktop. This will give you full information about the use of the PC. It will tell you about charging the battery, using the PC from mains and from battery.
Generally, to use a laptop from the battery you should check the battery is charged (see your manual for details), turn the charger off at the mains switch and unplug the charger lead from the laptop.