Laptops are common now; most people have them to take to school or when they travel for work.
Or that slideshow you have created (but carelessly forgot to save) may disappear if your laptop battery is not recharged.
As common as laptops are now, it is just as common to see individuals forgetting that the machine needs a little bit of help to run.
It does not magically power itself; the battery does not somehow manage to stay full as you work for hours at a time. Yet, many seem to think that their battery does just that. No matter how long they stay hunched over the machine, it will work.
A few times of having the laptop die will cure that fantasy.
The truth is: you must keep your laptop charged. Yes, one of the advantages of having a laptop is that you can take it anywhere; it does not require you to remain plugged into the wall.
And they do tell you. Laptops feature a symbol at the top of the screen that allows you to see just how much your battery is charged. The lower it drops, the less time you have.