How Many Years Does the Battery in a Prius Last?

I'm really considering buying a Prius because me and my family have been scraping pennies to put gas in the tank these days. My moms Ford Taurus just ran out of gas the other day and that was the last straw for me. We are dumping around 30 bucks a week of our hard earned cash into that car, and enough is... show more I'm really considering buying a Prius because me and my family have been scraping pennies to put gas in the tank these days. My moms Ford Taurus just ran out of gas the other day and that was the last straw for me. We are dumping around 30 bucks a week of our hard earned cash into that car, and enough is enough. I don't know much about hybrids or electric cars so I want to know how many years can I get out of the battery in the Prius before it needs to be replaced? Especially since i'm looking at a few used 2010 Prius' with around 37-47k miles on them. Are they low maintenance? What kind of gas savings can I expect to get? I just need reliable, low cost transportation back and forth to school.
Update: And I know there is an 8 year/100,000 mile warranty but will the battery last longer than that? I don't want to be replacing a battery every 8 years.
8 answers 8