With notebook completely idle and screen at 50% brightness: 239 minutes (3h 59m)
With screen at full brightness and using notebook constantly: 76 minutes (1h 16m) ASUS X54H Battery
The sad news is that if you're watching a DVD that's much over 1.5 hours it's going to be a struggle to make it all the way through without recharging. You can get a larger capacity battery that claims 50% more battery life, but it will stick out at the back and add weight to the laptop, the cost of that batte...