3 Hours is probably about right. The battery monitor is just an indicator of the battery life. When you charge it up fully from new it is not uncommon for it to say something ridiculous. As it calibrates itself it will become more accurate.
It`s rather like filling a car up with petrol, the guauge says full but as you drive it falls steadily and that last quarter tank disappears in about 15 miles!!
Obviously battery life depends on what you do on the computer. If you watch a DVD for example it will drain much quicker than if you`re just doing basic word processing.