In general, a laptop battery will last about 3-4 years before it degrades noticeably. If yours is much newer, make sure that you don't have background programs that are sucking up your processor. Microsoft has a a widget for Windows 7, and there are freeware versions for earlier O/S. Battery life is affected by how busy your processor is, and stated values are based on a pretty light load. Watching movies can take a LOT more power for instance and drain a battery in an hour or so.
If your laptop is 3-4 years old, I'd buy a cheap replacement off eBay. I got my last Compaq battery for about $15 all in from a place in Hong Kong. Lasted through the final two years of laptop life. At 4 years, your laptop is about 80% depreciated. Why spend top dollar for parts? Get the cheapest thing that will keep it going a bit longer. I am aware that there may be quality issues with 3rd party parts, but really would you buy top of the line parts for a very old car?