Are you talking about the length of the charge or the overall battery life?
If you're talking about the charge, most laptops will usually go for a few hours. As far as overall life goes, the batteries in all of my laptops usually died after a year or two and aren't typically covered by warranty.
You can probably run your laptop without a battery but if you want to hibernate it or something, you will need one.
"Blu-ray is just a bag of hurt." - Steve Jobs