The laptop can be run either by battery power or it can be plugged into a wall outlet with the AC Adapter.
Adapter is in laptop carrying case.
When using battery power, a small battery icon will appear. Hold the mouse pointer over the battery icon and a percentage of power or amount time left on battery. The laptop will notify you via a pop-up dialog box when the battery begins to run low. At that point you should save any work to a floppy disk. If you wish to continue working after a low battery warning, you should power the laptop with the AC adapter.