How to find a Replacement laptop battery?

I have a sony VGN Nr 160 E. It needs a new battery. Is there a replacement battery I can use with a longer half-life, because even when new, the battery life was supposedly a maximum of 4 hours ( actually much less).How to find a Replacement laptop battery?e-bay , batteries don't have %26quot;half lives%26quot; none of them last as long as claimed either in use or their actual lifeHow to find a Replacement laptop battery?Go to sony.com And do that one really