I have 107,000 miles on my 2004 Prius and the battery is fine. If it needs a new one after 10 years, well that's great longevity! Prius is one of the most reliable cars according to Consumers Report (and my experience too), so needing to pay $3K after 10 years for the battery is not so bad from an overall cost of operation POV. And since many people don't keep their cars more than 10 years, they won't face the battery issue at all (assuming they bought their car new!).