There will be a button near those lights that you can press. The number of lights that illuminate when you do this, will indicate its state of charge. Five lights is fully charged. Li-Ion batteries are intelligent devices nowadays, as in they have a microprocessor inside that monitors them. This is how the battery can talk to the PC; for example, the device manager will be able to tell you things like the battery's serial number, etc. The processor also learns your usage patterns, which is used to make the "time remaining" guestimate more and more accurate.