Notebook Battery Question

Do any of you know what the typical overall battery life for notebooks are?

I'm having an issue with my Sony VAIO notebook that I purchased in 2001 where, despite it being fully charged, it only lasts for about 10-20 minutes off of the AC Adaptor. Must I simply buy a new battery or is there a problem with the notebook itself that requires further attention?

If a new battery is a must, any preferences among you (seeing as how you are all far more knowledgable than I)?
 
Battery life

Battery life per charge obviously various a lot between machines and the sort of usage it has. Around 2 hours should be expected. My Thinkpad does nearly three hours on average.
 
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